Antoine Glicenstein

Giovanni Ferioli

Ludovic Brossard

Yvan R P Sortais

Daniel Barredo

Florence Nogrette

Igor Ferrier-Barbut

Antoine Browaeys

Fast and efficient preparation of 1D chains and dense cold atomic clouds

Keywords:

We report the efficient and fast (∼ 2 Hz) preparation of randomly loaded 1D chains of individual 87 Rb atoms and of dense atomic clouds trapped in optical tweezers using a new experimental platform. This platform is designed for the study of both structured and disordered atomic systems in free space. It is composed of two high-resolution optical systems perpendicular to each other, enhancing observation and manipulation capabilities. The setup includes a dynamically controllable telescope, which we use to vary the tweezer beam waist. A D1 Λ-enhanced gray molasses enhances the loading of the traps from a magneto-optical trap. Using these tools, we prepare chains of up to ∼ 100 atoms separated by ∼ 1 µm by retro-reflecting the tweezer light, hence producing a 1D optical lattice with strong transverse confinement. Dense atomic clouds with peak densities up to n 0 ∼ 10 15 at/cm 3 are obtained by compression of an initial cloud. This high density results into interatomic distances smaller than λ /(2π) for the D2 optical transitions, making it ideal to study light-induced interactions in dense samples.

II.

I. INTRODUCTION

The optical response of an ensemble of atoms illuminated by near-resonant light can be significantly different from the one of a single atom due to light induced dipole-dipole interactions [START_REF] Guerin | Light interacting with atomic ensembles: collective, cooperative and mesoscopic effects[END_REF]. They give rise to collective behaviors such as modified decay rates or spectral linewidths [START_REF] Araújo | Superradiance in a large and dilute cloud of cold atoms in the linear-optics regime[END_REF][START_REF] Roof | Observation of single-photon superradiance and the cooperative lamb shift in an extended sample of cold atoms[END_REF][START_REF] Guerin | Subradiance in a large cloud of cold atoms[END_REF][START_REF] Rui | A subradiant optical mirror formed by a single structured atomic layer[END_REF], or resonance shifts [START_REF] Corman | Transmission of near-resonant light through a dense slab of cold atoms[END_REF][START_REF] Jennewein | Coherent scattering of nearresonant light by a dense, microscopic cloud of cold two-level atoms: Experiment versus theory[END_REF][START_REF] Glicenstein | Collective shift in resonant light scattering by a one-dimensional atomic chain[END_REF]. Recently these effects have drawn an increasing interest, for they can be relevant in fundamental optics and have possible applications ranging from optical lattice atomic clocks [START_REF] Chang | Controlling dipole-dipole frequency shifts in a lattice-based optical atomic clock[END_REF][START_REF] Krämer | Optimized geometries for future generation optical lattice clocks[END_REF][START_REF] Bromley | Collective atomic scattering and motional effects in a dense coherent medium[END_REF] to quantum technologies [START_REF] Ostermann | Protected state enhanced quantum metrology with interacting two-level ensembles[END_REF][START_REF] Plankensteiner | Selective protected state preparation of coupled dissipative quantum emitters[END_REF].

In order to enhance the collective optical response of an atomic ensemble, two different paths can be followed. The first one consists in using high-density samples, so that the effect of light-induced dipole interactions is large. This requires the preparation of atomic clouds with densities n fulfilling n/k 3 ∼ 1 where k = 2π/λ 0 with λ 0 the atomic resonance wavelength. Fundamental questions arise concerning disordered ensembles, such as the existence of Dicke superradiance in small samples [START_REF] Friedberg | Limited superradiant damping of small samples[END_REF] or the saturation of the index of refraction for high densities [START_REF] Andreoli | The maximum refractive index of an atomic medium[END_REF]. In disordered clouds, the field radiated by each emitter acquires a random propagation phase that renders difficult the pristine control of interaction effects. The second path thus consists in spatially structuring the cloud at the sub-wavelength scale [START_REF] Bettles | Enhanced optical cross section via collective coupling of atomic dipoles in a 2d array[END_REF][START_REF] Shahmoon | Cooperative resonances in light scattering from two-dimensional atomic arrays[END_REF]. In this way, the interferences can be tailored, making it possible to enhance or suppress the effect of dipole interactions. This second route could pave the way to several applications: for example, mirrors made by an atomic layer [START_REF] Bettles | Enhanced optical cross section via collective coupling of atomic dipoles in a 2d array[END_REF][START_REF] Shahmoon | Cooperative resonances in light scattering from two-dimensional atomic arrays[END_REF][START_REF] Facchinetti | Interaction of light with planar lattices of atoms: Reflection, transmission, and cooperative magnetometry[END_REF], as recently realized using a 2D Mott insulator [START_REF] Rui | A subradiant optical mirror formed by a single structured atomic layer[END_REF], controlled transport of excitations [START_REF] Chui | Subwavelength transportation of light with atomic resonances[END_REF][START_REF] Needham | Subradianceprotected excitation transport[END_REF] and light storage [START_REF] Plankensteiner | Selective protected state preparation of coupled dissipative quantum emitters[END_REF][START_REF] Asenjo-Garcia | Exponential improvement in photon storage fidelities using subradiance and "selective radiance" in atomic arrays[END_REF] or in quantum metrology [START_REF] Ostermann | Protected state enhanced quantum metrology with interacting two-level ensembles[END_REF][START_REF] Plankensteiner | Selective protected state preparation of coupled dissipative quantum emitters[END_REF][START_REF] Facchinetti | Storing light with subradiant correlations in arrays of atoms[END_REF]. The investigation of collective effects in ordered ensembles is also relevant for optical lattice clocks [START_REF] Chang | Controlling dipole-dipole frequency shifts in a lattice-based optical atomic clock[END_REF][START_REF] Krämer | Optimized geometries for future generation optical lattice clocks[END_REF][START_REF] Campbell | A fermi-degenerate threedimensional optical lattice clock[END_REF], as they could limit their accuracy.

In this paper, we follow the two paths introduced above, relying on a new experimental platform, which we describe and characterize. This platform makes it possible to prepare 1D arrays [START_REF] Karski | Nearest-neighbor detection of atoms in a 1d optical lattice by fluorescence imaging[END_REF] of 87 Rb atoms, and disordered atomic ensembles with peak densities reaching n 0 /k 3 ∼ 1. This apparatus is an upgrade of our previous experimental setup [START_REF] Jennewein | Coherent scattering of nearresonant light by a dense, microscopic cloud of cold two-level atoms: Experiment versus theory[END_REF]. It consists of two high-resolution optical systems with axes perpendicular to one another in a "maltese cross" geometry similar to [START_REF] Bruno | Maltese cross coupling to individual cold atoms in free space[END_REF]. These two optical axes used together allow for the simultaneous observation of the fluorescence light emitted by the atoms (incoherent response [START_REF] Pellegrino | Observation of suppression of light scattering induced by dipole-dipole interactions in a cold-atom ensemble[END_REF]) and the transmission through the cloud (coherent part [START_REF] Jennewein | Propagation of light through small clouds of cold interacting atoms[END_REF]). One of the axes is used to focus a tight optical dipole trap (tweezer) to confine the atoms. We have placed in the tweezer beam path a telescope made of two lenses with tunable focal length to dynamically control the tweezer waist. We use this control to prepare chains of atoms with variable length when retro-reflecting the tweezer laser beam, and dense elongated samples after compressing an initially loaded atomic cloud. The loading of the traps from a cloud of laser cooled atoms is enhanced by implementing Λ-enhanced gray molasses.

The paper is organized as follows. Section II describes the optical setup and its alignment, the imaging system, and the OptoTelescope that allows to produce optical tweezers with tunable waists. Section III presents the realization of a 1D chain with controllable length and its characterization. Section IV details the enhancement of the trap loading using gray molasses. Section V introduces a new protocol to prepare dense clouds using the tools described before.

Trapping individual atoms or preparing dense atomic samples requires the waist of the dipole trap beam to be on the order of a few micrometers [START_REF] Schlosser | Collisional blockade in microscopic optical dipole traps[END_REF][START_REF] Bourgain | Evaporative cooling of a small number of atoms in a single-beam microscopic dipole trap[END_REF]. This imposes to work with high numerical aperture (NA), diffraction-limited lenses [START_REF] Sortais | Diffraction-limited optics for single-atom manipulation[END_REF]. As represented in Fig. 1 The trap radial size is dynamically controlled with the OptoTelescope (OT). All light enters and exits the vacuum chamber through CF40 viewports (Vp). Insert : The x-axis is rotated by an angle of 45°with respect to the plane containing the horizontal beams of the MOT and the z-axis. It is therefore not superimposed to the vertical beam of the MOT, which is in the direction of gravity g .

four in-vacuum aspheric lenses, forming two orthogonal axes in a quasi-confocal configuration. The lenses are manufactured by Asphericon ® [31] and feature effective NA = 0.44. Their working distance (15 mm) is sufficiently large to allow for large optical access, in particular for the six counterpropagating magneto-optical trap (MOT) beams. The plane containing the optical axes of the lenses makes an angle of 45 • with respect to the one containing horizontal MOT beams (see Insert Fig. 1): this gives an extra (vertical) access for the atomic beam entering the trapping region. This configuration allows the six MOT beams to be orthogonal, which facilitates alignment and the overlapping with the dipole trap. This also reduces the stray light scattered in the chamber and collected by the imaging system. The conjugated planes has been optimized using an optical design software to minimize the aberrations of the two crossed optical systems, at both the trapping wavelength λ trap = 940 nm and the 87 Rb D2 line (λ 0 = 780 nm), the numerical aperture being fixed. Due to the dispersion properties of the glass of the aspheric lenses, the best performances at λ trap and λ 0 are achieved at different focusing positions for initially collimated beams. For this reason, we work in a tradeoff configuration where the optical performances of the lenses are similar for the two different wavelengths. More precisely, we impose that the wavelength-dependent Strehl ratio (S) [START_REF] Max Born | Principles of optics[END_REF] is the same at λ trap and λ 0 . In our specific case, we calculate S = 0.93, at a distance d = +285 µm away from the focal point of a lens at λ 0 . For this configuration, we calculate that 2. Sketch of the alignment procedure. A CCD camera is placed at a fixed position d 780 while we shine a λ 0 = 780 nm laser beam onto a pinhole acting as a point source for the aspheric lens A. By moving the pinhole with respect to lens A, we optimize the Strehl ratio on the camera and have access to the best focus of this lens. The pinhole is then rotated to face the other lenses.

the image of an object emitting in vacuum at λ 0 is located at d 780 1119 mm in air (see Fig. 2). This distance is used for the alignment procedure of the lenses described in the next section.

B. In-vacuum lenses alignment

The alignment procedure is detailed in [START_REF] Brossard | Study of light-induced dipolar interactions in cold atoms assemblies[END_REF]. It is experimentally challenging as it involves intersecting two optical axes with a precision much smaller than their field of view (±50 µm) [34]. We did the alignment in air, correcting for the difference in index of refraction with respect to vacuum. The barrels holding the aspheric lenses are placed inside a metallic lens holder and separated from it with glass spacers. The lens holder is designed such that the angle formed between the two axes is 90°with a tolerance of ±0.1°. The only degree of freedom for each lens is its on-axis position. It is set by tuning the thickness of the glass spacers with a precision of ±1 µm. As represented in Fig. 2, a CCD camera is first placed at a distance d 780 away from one lens. A pinhole of diameter (1.0 ± 0.5) µm is then mounted on an XYZ translation stage and a rotation stage and placed inside the lens holder. This pinhole is not small enough to be considered as a point source when illuminated by a laser beam at λ 0 . We have taken its finite size into account for the characterization of the performance of the lenses [START_REF] Brossard | Study of light-induced dipolar interactions in cold atoms assemblies[END_REF]. The pinhole is first moved parallel to the lens axis to minimize the size of its image on the CCD. Once the pinhole is in the targeted object plane, we move it in the transverse plane to maximize the Strehl ratio, thus placing it on the lens optical axis. The pinhole is then rotated by 90 • to face another lens. This procedure is performed for each lens and by keeping track of the pinhole motion, we obtain a mapping of the best foci. Finally, the spacers thickness is adjusted to bring all the foci at the same point. After the procedure, we obtain a satisfying alignment of the lenses and the optical axes cross with a residual offset 5 µm, smaller than the field of view of the lenses.

C. Imaging system

The atoms held in the dipole trap are imaged with the two high-resolution axes (Fig. 1), with a diffraction-limited resolution of 1.22λ 0 /(2NA) 1 µm. Along the trapping axis ẑ, the fluorescence or the transmitted light is separated from the trap light using a dichroic mirror and interferometric filters, and is collected by an electron-multiplying CCD (EMCCD) with pixel size 16 µm × 16 µm [START_REF][END_REF]. The magnification of the imaging system along this axis is 6.4, leading to an effective pixel size in the object plane of 2.5 µm: this allows focusing the light emitted by a single trapped atom onto a single pixel, maximizing the signal-to-noise ratio, albeit at the cost of a lowered resolution with respect to the diffraction limit. The fluorescence emitted along the x-axis is collected on the same camera, allowing for the observation of the atoms in two orthogonal directions in a single image. The magnification on the transverse axis is ∼ 16, leading to an effective pixel size of 1 µm in the object plane. Both resolutions were verified using calibrated pinholes in planes conjugate to the atoms plane. The magnification was confirmed by measuring simultaneously the displacement of trapped atoms on both axes when moving the trapping beam by a known distance. The estimated collection efficiency of both imaging systems is ∼ 4%, taking into account the collection of the aspheric lens (5%), the transmission of the optical elements (90%) and the camera quantum efficiency (85% at λ 0 = 780 nm). This value is confirmed by the measurement of the fluorescence at saturation of a single 87 Rb atom in a tight dipole trap. As detailed below, we use this atom as a probe to characterize the trap (size and depth), as was done in [START_REF] Sortais | Diffraction-limited optics for single-atom manipulation[END_REF].

D. The OptoTelescope

Our apparatus includes a telescope with tunable magnification, which we name here OptoTelescope (OT). This telescope is composed of a pair of 1 inch lenses with voltage-controlled focal lengths, manufactured by OptoTune ® [36], and placed in an afocal configuration. Tunable lenses allow for the dynamical manipulation of dipole traps [START_REF] Léonard | Optical transport and manipulation of an ultracold atomic cloud using focus-tunable lenses[END_REF]. Here, using the OT, we dynamically change the size of the trapping beam before the aspherical lens and thus the optical tweezer waist. To limit aberrations from the OT, we use a beam diameter of 1 mm at its entrance. Also, we minimize gravity-induced aberrations by positioning the optical axis of the lenses vertically. In order to achieve small waists on the atoms, the beam after the OT is magnified by a ×4 telescope before being focused by the aspherical lens. The OT is designed for a magnification ranging from 1 to 3.5.

We characterized the OptoTelescope by performing in situ measurements on a single atom trapped in the tweezer. For a given magnification, the waist of the trap w 0 is measured as follows. For a fixed power P, the peak intensity and thus the light-shift induced by the trap (proportional to the trap depth U) are obtained by using a push-out beam expelling the atom from the trap. The light shift is measured from the detuning of this beam for which the push-out effect is the largest, recorded for various trap depths. The trap waist is then extracted using U ∝ P/w 2 0 . The results were checked by independent measurements of the oscillation frequencies of individual trapped atoms [START_REF] Sortais | Diffraction-limited optics for single-atom manipulation[END_REF]. We are able to dynamically change the size of the trap between about 1.6 µm and 4.3 µm, in agreement with the theoretical values calculated using gaussian optics, as shown in Fig. 3.

III. REALIZATION OF A CHAIN OF ATOMS WITH CONTROLLABLE LENGTH

In this section, we present the preparation and characterization of one-dimensional atomic chains of cold Rb atoms, using the tools described in the previous section.

As represented in Fig. 1, we produce the chain by retroreflecting the tweezer beam using the second aspherical lenses placed on the same axis, thus forming a 1D optical lattice with an inter-site spacing λ trap /2 = 470 nm [START_REF]cause of the transmission through all the optical elements[END_REF]. The small beam waist of the tweezer ensures a tight transverse confinement. This 1D array in then loaded from the MOT with a filling fraction averaged along the chain of 0.25. We will show in the next section that the loading can be improved up to ∼ 0.5 using gray molasses. We collect the fluorescence emitted by the chain in the transverse direction under a 20 ms excitation by the MOT beams. A typical example of the atomic chain is shown in Fig. 4(a) (the resolution being about twice the intertrap separation, we do not resolve individual sites). The length of the atomic chain is given by the range around the focal point where the beam intensity is high enough to trap atoms, which is set by the Rayleigh distance z R = πw 2 0 /λ trap . Experimentally, we realize atomic chains with different lengths (and atom number) by tuning the waist of the trapping beam using the OT. As changing the waist also modifies the trap depth, we adapt its power to keep the depth at the center of the chain at ∼ 1 mK. In Fig. 4 To characterize the chain, we measure the local transverse and longitudinal trapping frequencies ω r and ω z along the chain axis. To do so, we rely on parametric heating by modulating the intensity of the trapping beam at a given frequency, inducing losses at 2ω r or 2ω z . Since the trap depth varies along the chain, the oscillation frequencies depend on the position, and so do the resonant frequencies of the parametric heating. Experimentally, we first load a chain from the MOT and take a first reference fluorescence image. The trap beam power is then set at a value of 140 mW while, for this measurement, the waist is set to 3.3 µm. With these parameters we expect ω z 2π × 1 MHz and ω r 2π × 70 kHz at the center of the chain. The beam intensity is then modulated with a relative amplitude of 5% during 100 ms using an arbitrary waveform generator. A second fluorescence image of the chain is then taken and compared to the reference image to evaluate the atom losses. This sequence is repeated 50 times to average over the chain filling.

Figure 5 shows the atom losses due to the axial excitation. The resonance frequencies extracted with this method are in good agreement with the calculated oscillation frequencies (dashed lines), confirming the expected value of the waist. The different dashed lines reported in Fig. 5, are given by 2ω z /p with p integer. We observe losses at these frequencies since the amplitude modulation is not perfectly sinusoidal and thus contains tones at multiples p of the driving frequency. We also observe losses on the chain edges where the trap is the shallowest: these are due to the reference imaging light expelling atoms from the shallow traps, which are thus not recovered in the second fluorescence image. The same experiment was done for radial oscillation frequencies, obtaining also in this case a good agreement between the measured trapping frequencies and the predicted ones.

IV. OPTIMIZATION OF THE LOADING USING Λ-ENHANCED GRAY MOLASSES

Gray molasses (GM) are commonly used to achieve sub-Doppler cooling of atoms using dark states [START_REF] Grynberg | Proposal for a magneto-optical lattice for trapping atoms in nearly-dark states[END_REF][START_REF] Boiron | Three-dimensional cooling of cesium atoms in four-beam gray optical molasses[END_REF][START_REF] Boiron | Laser cooling of cesium atoms in gray optical molasses down to 1.1 µk[END_REF][START_REF] Esslinger | Purely optical dark lattice[END_REF][START_REF] Fernandes | Sub-doppler laser cooling of fermionic 40 k atoms in three-dimensional gray optical molasses[END_REF]. The use of GM in a tight optical tweezer offers two interesting prospects. First, the low photon scattering rate in dark states reduces light-induced collisions. This yields a higher density of the atomic cloud the tweezer is loaded from, and hence a larger number of atoms in the tweezer. Second, their blue detuning with respect to the atomic frequency should permit to tailor light-induced collisions to selectively remove a single atom out of a pair, resulting into exactly one atom per trap with high probability [START_REF] Grünzweig | Near-deterministic preparation of a single atom in an optical microtrap[END_REF][START_REF] Brown | Gray-Molasses Optical-Tweezer Loading: Controlling Collisions for Scaling Atom-Array Assembly[END_REF].

We first consider the loading of a single atom in a small (non-retroreflected) tweezer, and apply Λ-enhanced gray molasses [START_REF] Grier | Λ-enhanced sub-Doppler cooling of lithium atoms in D1 gray molasses[END_REF] on the 87 Rb D2 line (λ 0 = 780 nm) [START_REF] Rosi | Λ-enhanced grey molasses on the D 2 transition of Rubidium-87 atoms[END_REF]. The cooling beam is blue-detuned from the (5S 1/2 , F = 2) to (5P 3/2 , F = 2) transition and superimposed with the six MOT beams with intensity I ∼ I sat = 1.67 mW cm -2 per beam. The coherent repumper is created from the same laser using an electro-optical modulator with frequency equal to the ground state hyperfine splitting ν = 6834.68 MHz. The intensity of the repumper is I ∼ I sat /10 per beam, given by the sideband amplitude. Since gray molasses rely on the blue detuning of the cooling lasers, the optimal detuning will depend on the light-shift induced by the tweezer beam. After the MOT beams are switched off, we study the loading of a single atom from the GM into the tweezer (waist w 0 = 1.6 µm) varying the detuning of the GM and the trap depth. For each set of parameters, we record the loading probability and the atom temperature, using a release and recapture method [START_REF] Sortais | Diffraction-limited optics for single-atom manipulation[END_REF][START_REF] Tuchendler | Energy distribution and cooling of a single atom in an optical tweezer[END_REF]. We have found that using the GM on the D2 line does result into individual atoms in the tweezer being colder than when loaded directly from the MOT (∼ 20 µK instead of 80 µK), and for a much broader range of the tweezer depth. Also, when loading directly from the MOT, the atoms can be captured in traps with depth U/k B ∼ 1 mK while applying the GM stage allows trapping for depth down to U/k B ∼ 200 µK. Furthermore, we observe that the GM detuning does not significantly change the temperature or the loading over a wide range of parame- ters for detunings between 50 and 120 MHz above the transition and depths U/k B between 200 µK and 1 mK. For larger trap depths and small detunings, the GM frequency becomes resonant with the (5S 1/2 , F = 2) to (5P 3/2 , F = 2) transition, resulting in heating of the atom. However, while we observe efficient cooling when applying the GM, we have not found loading probabilities significantly higher than 50% in a single tweezer, or 25% in chains of traps (retroreflected tweezers), similar to what we achieved with the MOT. This might be due to the fact that the blue-detuned beam on the (5S 1/2 , F = 2) to (5P 3/2 , F = 2) transition is detuned to the red of the (5S 1/2 , F = 2) to (5P 3/2 , F = 3) transition (267 MHz higher in frequency), causing light-induced collisions, which may limit the loading.

To circumvent this issue, we have thus implemented gray molasses on the D1 line [(5S 1/2 , F = 2) to (5P 1/2 , F = 2) transition]. In the single non-retroreflected tweezer, after optimization, we were not able to obtain individual atoms with a probability significantly higher than 50%, whatever the detuning. This is in contrast to what was reported using a bluedetuned beam [START_REF] Grünzweig | Near-deterministic preparation of a single atom in an optical microtrap[END_REF] or GM on the D1 line [START_REF] Brown | Gray-Molasses Optical-Tweezer Loading: Controlling Collisions for Scaling Atom-Array Assembly[END_REF]. To explain this observation, we compare the volume of our tweezer to the one used in Ref. [START_REF] Brown | Gray-Molasses Optical-Tweezer Loading: Controlling Collisions for Scaling Atom-Array Assembly[END_REF] and estimate ours to be a factor of > 10 larger. Thus our collision rate is reduced by this factor and the time for blue-detuned light-induced collisions to induce selective losses and leave a single atom in the trap should be much longer than experimentally achievable timescales. We thus infer that more than one atom are left inside the trap. To confirm this, we compare the result of loading via the GM, with the direct loading from the MOT. In one case, we load directly the trap from the MOT: the collisional blockade mechanism operates [START_REF] Schlosser | Collisional blockade in microscopic optical dipole traps[END_REF][START_REF] Sortais | Diffraction-limited optics for single-atom manipulation[END_REF] and when sending near resonant light for imaging, we observe two clear fluorescence levels corresponding to either 1 or 0 atom in the trap. In the other case, we apply a 200 ms-long GM to load the trap and then image the atoms as before. Under this condition, we record a broad fluorescence histogram, as shown in Fig. 6. We explain it by the fact that the initial atom number is large. However the imaging light induces strong losses removing the atoms during the imaging time thus preventing us from counting precisely the in-situ atom number.

Finally, we have used D1 gray molasses to improve the loading of the atom chain. We are now able to load a chain of traps with a 50% probability. This is likely due to the fact that on average there are more than one atom per site following the gray molasses loading. The application of the MOT light for imaging then induces strong light-induced collisions, leaving either 0 or 1 atom. Further investigations will be necessary to unravel the loading mechanism of this chain of closely-spaced traps by D1 λ -enhanced gray molasses. We have also found that the loading using GM is more stable than the direct loading from the MOT in terms of daily fluctuations.

V. PREPARATION OF DENSE ATOMIC CLOUDS

As mentioned in the introduction, one of the motivations for our new set-up is the study of light scattering in dense ensembles. We present here a loading protocol based on the new tools of the setup that allows preparing dense enough samples. The main idea is to load as many atoms as possible into a large single-beam dipole trap using GM on the D1 line, and compress the cloud by dynamically reducing the beam waist [START_REF] Kinoshita | All-optical boseeinstein condensation using a compressible crossed dipole trap[END_REF] using the OptoTelescope.

We start from a 3D-MOT, which is compressed in 15 ms by red-detuning the MOT beams from -3Γ to -5Γ. We then decrease the magnetic field gradient by 50%. The MOT beams are then switched off and the GM is applied for 200 ms, with the dipole trap on. At this stage, the trap depth is U/k B 4.2 mK and the waist is w 0 2.5 µm [START_REF]focal posi-tion when compressing a cloud, inducing significant heating and atom losses[END_REF]. In this starting configuration, we trap up to 6000 atoms at a temperature of 625 µK yielding a peak density n 0 ≈ 1.6 × 10 14 at/cm 3 . The use of GM is the key ingredient here that allows for the loading of this large number of atoms. The cloud has an aspect ratio of about 12 along the trapping axis. The atom number is evaluated from the fluorescence collected during the illumination of the cloud with a 10 µs-pulse of resonant light and dividing the signal by the same quantity measured with a single atom. To avoid effects caused by light-induced interactions, the imaging pulse in sent after a time-of-flight of 10 µs during which the density drops by about an order of magnitude [51]. The temperature is measured by fitting the cloud size for a variable time-of-flight.

The trap is then compressed to a waist w 0 = 1.8 µm by changing the magnification of the OptoTelescope in 30 ms, keeping the power constant. Next, the trap depth is increased in 10 ms up to 7.6 mK. The duration of the compression has been optimized to be short enough to minimize three-body losses but long enough compared to the response time of the OT lenses (2.5 ms). At this stage, we obtain a cloud of about 2500 atoms in the trap at a temperature of 700 µK, which corresponds to a cloud peak density n 0 ∼ 10 15 at/cm 3 or equivalently to n 0 /k 3 = 1.7 ± 0.3. This density is three times larger than the one obtained in clouds of ∼ 500 atoms [START_REF] Pellegrino | Observation of suppression of light scattering induced by dipole-dipole interactions in a cold-atom ensemble[END_REF][START_REF] Bourgain | Evaporative cooling of a small number of atoms in a single-beam microscopic dipole trap[END_REF] with our previous apparatus which relied on a first, large dipole trap acting as a reservoir to load a second small tweezer. Such a high density results in large 3-body losses and high elastic collision rates. To characterize them and confirm the extracted value of the density, we study its dynamics. To do so, we have measured the cloud atom number N and temperature T as a function of the time after the end of the compression. The results are shown in Fig. 7(a). The temporal evolution of N and T is described by the following system of coupled equations that takes into account of 2-and 3-body losses [START_REF] Bourgain | Evaporative cooling of a small number of atoms in a single-beam microscopic dipole trap[END_REF][START_REF] Luiten | Kinetic theory of the evaporative cooling of a trapped gas[END_REF][START_REF] Eismann | Universal loss dynamics in a unitary bose gas[END_REF]:

dN dt = -γ 3 N 3 T 5 -γ 2 (σ (T ), T ) N 2 T (1)
dT dt = T 3 5 3 γ 3 N 2 T 5 -γ2 (σ (T ), T ) N T (2)
where the parameter γ 3 depends on the trap geometry and is proportional to the 3-body losses coefficient L 3 . The coefficients γ 2 and γ2 depend on the temperature, the trap geometry and on the two-body elastic cross-section σ (T ), whose temperature dependence takes into account the d-wave resonance at 350 µK. We interpolate the data of [START_REF] Buggle | Interferometric determination of the s and d-wave scattering amplitudes in87Rb[END_REF] to find a functional form of σ (T ). We fit the decay of the atom number with the solution of Eq. ( 1), leaving solely L 3 as a fit parameter. We obtain L 3 = (4 ± 1) × 10 -28 cm 6 /s. This value is larger [55] than those found in the literature [START_REF] Söding | Three-body decay of a rubidium Bose-Einstein condensate[END_REF][START_REF] Burt | Coherence, correlations, and collisions: What one learns about Bose-Einstein condensates from their decay[END_REF].

Note that there exists no prediction for the effect of the dwave resonance on 3-body losses, which could enhance L 3 at T = 650 µK. We thus do not expect to find the literature values, which were measured deep in the s-wave regime. We also compare the model prediction of the temperature evolution to the data [see Fig. 7(b)], and find a very good agreement. The temperature is almost constant, which justifies the assumption of a temperature-independent L 3 (and hence γ 3 ) in the model. Combining the measurements of the atom number and of the temperature, we calculate the cloud density. Its evolution is shown in Fig. 7(c).

Our experiment is therefore able to efficiently produce microscopic clouds containing up to a few thousand atoms at densities n 0 ∼ k 3 . This corresponds to the regime where the atoms become strongly coupled by light-induced resonant dipole-dipole interactions (scaling as hΓ/(kr) α with α = 1, 2, 3). Moreover the repetition rate of the experiment is high: about 2 Hz, limited by the MOT loading. Thanks to this, fast data acquisition is possible, which has allowed us to observe and control subradiance in the time domain [START_REF] Ferioli | Storage and release of subradiant excitations in a dense atomic cloud[END_REF]. It is in addition a strong asset when measuring, e.g., intensity correlations of the light emitted by the atomic ensemble.

VI. CONCLUSION

We have built an experimental setup that is well-suited for the study of light scattering in cold atom ensembles either in an ordered or disordered configuration. Our platform combines two high-resolution optical systems perpendicular to each other, an optical tweezer with a dynamically tunable waist and gray molasses on the D1 line. By retroreflecting the optical tweezer we create an optical lattice of controllable length, allowing for the preparation of atomic arrays with an average interatomic distance 1.2 λ 0 . We recently used this feature to investigate a collective enhancement of lightinduced interactions in 1D arrays [START_REF] Glicenstein | Collective shift in resonant light scattering by a one-dimensional atomic chain[END_REF][START_REF] Sutherland | Collective dipole-dipole interactions in an atomic array[END_REF]. The same strategy can be applied with an optical lattice of shorter wavelength (e.g. combining a repulsive optical lattice at 532 nm with the infrared tweezer for confinement). This would increase collective effects even further, enabling the observation of subradiant modes in ordered arrays [START_REF] Asenjo-Garcia | Exponential improvement in photon storage fidelities using subradiance and "selective radiance" in atomic arrays[END_REF][START_REF] Bettles | Cooperative eigenmodes and scattering in one-dimensional atomic arrays[END_REF]. Furthermore, we presented a protocol for preparing dense clouds in a tightly focused optical tweezer that exploits the dynamical tunability of the OT. In this way we create clouds with a peak density larger than k 3 at a rate > 2 Hz. The short inter-atomic distances reached in this configuration also offers interesting prospects for investigations of superradiance in small ensembles and subradiance as we recently reported in [START_REF] Ferioli | Storage and release of subradiant excitations in a dense atomic cloud[END_REF], as well as the study of fundamental questions such as the saturation of the refractive index of dense media [START_REF] Andreoli | The maximum refractive index of an atomic medium[END_REF].

FIG. 1 .

 1 FIG.1. Schematic of the experimental setup. Two orthogonal highresolution (NA=0.44) optical systems based on 4 in-vacuum aspheric lenses (AL) create an optical dipole trap, which can be retroreflected to realize a chain of single atoms in a 1D-optical lattice, and collect the scattered light on an electron-multiplying CCD (EMCCD) in two perpendicular directions. On the tweezer axis, the fluorescence is separated from the trapping light using a dichroic mirror (DM). The trap radial size is dynamically controlled with the OptoTelescope (OT). All light enters and exits the vacuum chamber through CF40 viewports (Vp). Insert : The x-axis is rotated by an angle of 45°with respect to the plane containing the horizontal beams of the MOT and the z-axis. It is therefore not superimposed to the vertical beam of the MOT, which is in the direction of gravity g .

  FIG.2. Sketch of the alignment procedure. A CCD camera is placed at a fixed position d 780 while we shine a λ 0 = 780 nm laser beam onto a pinhole acting as a point source for the aspheric lens A. By moving the pinhole with respect to lens A, we optimize the Strehl ratio on the camera and have access to the best focus of this lens. The pinhole is then rotated to face the other lenses.

1 FIG. 3 .

 13 FIG.3. Dipole trap waist at 1/e 2 as a function of the OT magnification. The diffraction limit 1.22λ trap /2NA 1.15 µm is indicated as the smallest trap achievable with the apparatus. The dashed line corresponds to the expected size.

  (b) we present cuts of the fluorescence along the chain for various lengths. Our longest chains have lengths of ∼ 100 µm (hence ∼ 200 sites).

1 FIG. 4 . 1 FIG. 5 .

 1415 FIG. 4. (a) Averaged image of the fluorescence collected by the transverse imaging axis. (b) Cuts of the fluorescence along the chain for various chain lengths.

1 FIG. 6 .

 16 FIG.6. Histogram of the collected fluorescence of atoms in a trap loaded with the GM (blue), in comparison with a trap loaded with a single atom (red). The fluorescence is induced in both cases by 20 ms of MOT beams with detuning 3Γ, where Γ is the natural linewidth of the 87 Rb D2 line. A background image, without atom, has been subtracted.

density n 0 /k 3 1 FIG. 7 .

 17 FIG. 7. Time evolution in the final trap of atom number (a) and temperature (b). In (a) and (b), the solid lines correspond to the solutions of (1) and (2) with L 3 as single fit parameter. (c) Peak density n 0 in the trap, deduced from (a) and (b).

ACKNOWLEDGMENTS

We thank Brandon Grinkenmeyer for early work in the construction of the apparatus. This project has received funding from the European Union's Horizon 2020 research and innovation program under Grant Agreement No. 817482 (PASQuanS) and by the Région Île-de-France in the framework of DIM SIRTEQ (project DSHAPE) and DIM Nano-K (project ECONOMIQUE). A. G. is supported by the Délégation Générale de l'Armement Fellowship No. 2018.60.0027.


Chiara Arrighi
email: chiara.arrighi@unifi.it

Francesco Ballio

Francesca Carisi

Fabio Castelli

Alessio Domeneghetti

Alice Gallazzi

Marta Galliani

Frédéric Grelot

Patric Kellermann

Heidi Kreibich

Daniela Molinari

Guilherme S Mohor

Markus Mosimann

Stephanie Natho

Claire Richert

Kai Schroeter

Anna Rita Scorzini

Annegret H Thieken

Andreas P Zischg

A comparative analysis of flood damage models: lessons learnt and future challenges

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

The estimation of flood losses implies the use of vulnerability/exposure models for flood damage and risk assessment (Meyer et al. 2013;[START_REF] Zischg | Validation of 2D flood models with insurance claims[END_REF][START_REF] Wagenaar | Regional and Temporal Transferability of Multivariable Flood Damage Models[END_REF][START_REF] Molinari | Validation of flood risk models: Current practice and possible improvements[END_REF]). According to [START_REF] Gerl | A Review of Flood Loss Models as Basis for Harmonization and Benchmarking[END_REF], in central Europe there are 28 models with 652 functions to assess flood losses, whereas almost half of the functions refer to residential buildings. The main differences among damage models are: (i) spatial scale, (ii) metric (i.e. absolute or relative loss), (iii) exposure assessment (i.e. whole building or affected floors, market values or reconstruction-replacement costs), (iv) number of input variables, (v) calibration/validation with observed losses. These differences pose the issue of model transferability to other urban or environmental contexts. With a joint effort of eight research groups, the objective of this study is to test and compare damage models for residential buildings used or developed by each group, by applying them in a "blind exercise", i.e. a common flood case study characterised by high availability of hazard and building data, with unknown information on observed losses in the implementation stage of the models. As the research groups use approaches representing many different types and characteristics of models (e.g. univariable -multivariable; absolute -relative; graduated -regression -machine learning), being calibrated based on empirical data stemming from different countries (Austria, France, Germany, Italy, Japan, Netherlands), with different landscapes, the blind exercise provides an extensive comparison of models and their transferability. The analysis of the differences in the ensemble of model outcomes aims at pointing out common patterns or divergent behaviours between model outcomes and with respect to observed losses.

Method

Nine damage models for residential buildings were selected for the study. They are shortly described below; further model details can be found in the respective references and in Molinari et

Case study

The study area is the town of Lodi (Italy), which in November 2002 was hit by a flood, caused by the overflow of the Adda River, which caused severe losses to buildings and economic activities. The event was chosen as reference for the exercise because it is well documented and hazard, exposure and vulnerability data are available. A 2D hydraulic reconstruction of the event is also available FLOODrisk 2020 -4 th European Conference on Flood Risk Management [START_REF] Scorzini | A New Tool to Estimate Inundation Depths by Spatial Interpolation (RAPIDE) Design, Application and act on Quantitative Assessment of Flood Damage[END_REF], as well as micro-scale information on exposure and vulnerability of residential buildings. Observed damage is known for 345 of the 877 flooded buildings, as derived from claims compiled by citizens after the occurrence of the flood, to ask for public compensation. Claim data have been stored in a georeferenced database by a team of researchers of Politecnico di Milano including information on the owner, the address of the flooded building, its typology (e.g. apartment, single house), the number of affected floors, a description of the physical damage and its translation in monetary terms (distinguishing, for the different rooms the building is made of, among damage to walls, windows and doors, floor, systems and content).

Results and discussion

In order to identify commonalities and dissimilarities among the different flood damage models, first, exposure estimates were compared, and, second, estimated losses have been compared to observed losses. Table 1 shows the Pearson correlation coefficient for the estimated exposure. Although there are 9 models, exposure assessment can be common to different approaches, e.g. the models by [START_REF] Dutta | A mathematical model for flood loss estimation[END_REF], Fuchs et al. ( 2019), [START_REF] Jonkman | Integrated hydrodynamic and economic modelling of flood damage in the Netherlands[END_REF]. Table 1 shows very high correlation coefficients, meaning that all models start with a very similar approach for exposure assessment, although models have been developed for different contexts and different available data. The average of the 9 damage models is 22 M€ that is about four times the observed loss. The model by [START_REF] Dutta | A mathematical model for flood loss estimation[END_REF] provides the higher estimate, more than twelve times the observed 6 M€. These differences can be easily observed also in the maps of Fig. 12, where the model outcomes and observed losses are represented. Given the number of maps, the results have been separated into two figures to ensure readability. Figures 12show with the same colour scale the estimated unitary losses (Fig. 12, panels b to j) and the observed losses (Fig. 1, panel a). Also in the case of the model by Arrighi et al. (2018), which provides the closest estimate of the overall losses, the maps (Fig. 1, panels a, b) show several differences. In fact, although the estimates are close to observations we may notice that the model behaves 'smoothly' where water depths are quite homogenous (see the right hand side of the map, panel b) while observed losses (panel a) appear more variable in space, with very high and very low damages close one to another. This smoothing effect, although with different absolute values can be observed in all models, highlighting that single-building scale flood damage estimation is very challenging for modellers given the intrinsic variability and uncertainty of exposure and vulnerability at such small scale.

Conclusions

The blind test suggests that model transferability depends on the similarity between the area of implementation and the calibration context. In fact, models developed for the Italian studies performed generally better than others. Nevertheless, the maps show that models provide a smoother estimation with respect to actual claims, which is affected by high spatial variability and uncertainty at single-building scale.

a Corresponding author: chiara.arrighi@unifi.it DOI 10.3311/FLOODRisk2020.9.15 a Corresponding author: chiara.arrighi@unifi.it DOI 10.3311/FLOODRisk2020.9.15 This result suggests that a decrease in scale of application, e.g. census section (i.e. building block) or neighbourhood, could have positive effects in terms of capability of intercepting mean loss values.

Literature (e.g. [START_REF] Merz | Multivariate flood damage assessment: a tree-based datamining approach[END_REF] generally suggests that including more variables in the models can improve accuracy, however in this blind test the simpler models (Carisi-sqrtmono or [START_REF] Jonkman | Integrated hydrodynamic and economic modelling of flood damage in the Netherlands[END_REF] provide estimates comparable to multi-variable models (e.g. FLEMO-ps, CEPRI).

Further research could better investigate scale effects and observation uncertainties to improve the understanding of flood damage estimation.

Figure 1 .

 1 Figure 1. Comparative maps of unitary damage model estimates (b-g) and observed losses (a) (part 1)

Figure 2 .

 2 Figure 2. Comparative maps of unitary damage model estimates (h-j) (part 2)

  to house building tradition of the Alps and flood processes with sediment transport. The model supplies a relative damage, i.e. the degree of loss that describes the ratio of loss to the replacement value of the whole building.-INSYDE[START_REF] Dottori | a synthetic, probabilistic flood damage model based on explicit cost analysis[END_REF]

		2017) is an expert-based synthetic model
		developed for the Italian context. INSYDE
		adopts 23 input variables, six describing the flood
		event and 17 referring to building features. The
		model supplies damage in absolute terms by
		considering the replacement/recovery value of
		damaged components, and by referring only to
	al. (2020): -the model by Arrighi et al. (2018a, 2018b) is a synthetic model which associates a relative physical damage to flood depth and then calculates a monetary damage as a function of the recovery cost (as a fraction of market value). The relative damage is calculated through two piece-wise linear stage-damage curves for buildings with and without basement. The model was created based on expert judgement for the city of Florence (Italy) and applied both at building and census block scale (Arrighi et al. 2018a, 2018b) -The model developed by CEPRI (European Center for Flood Risk Prevention) is a synthetic multi-variable model expressing absolute damage as the expected sum of the actions required after a flood to go back to the pre-flood state. Water depth, submersion duration and building characteristics are considered (CEPRI, 2014a, b; Richert & Grelot, 2018). -The model by Dutta et al. (2003) is a simple model considering flood depth only. The model supplies a relative damage, i.e. the degree of loss that describes the ratio of loss to the replacement value of the whole building; basement, number of exposed floors or other exposure variables are not separate inputs for the model, but are part of its variance. -FLEMOps (Flood Loss Estimation MOdel for the private household sector) is a multi-variable, rule-based model estimating relative monetary flood loss to residential buildings as a function of water depth, building type and building quality, whereby it is not further differentiated between flooded floors, and the (non-)existence of a	flooded floors (including basement, if present). It was validated for different Italian flood events (Dottori et al., 2016; Molinari et al. 2017; Amadio et al. 2019). -The model by Jonkman et al. (2008) is a simple model considering flow depth as the only explicative variable, calibrated on loss data in the Netherlands. As for Dutta et al. (2003) and Fuchs et al. (2019), the model supplies damage in relative terms. -Carisi_MV (Carisi et al. 2018) is an empirical multi-variable model based on random forest approach, which estimates relative building losses considering six explicative variables: maximum water depth, maximum flow velocity, flood duration, monetary building value per unit area (based on market value), structural typology and footprint area of each building (Carisi et al. 2018). Calibration data come from a real inundation event by the Secchia river, in the province of Modena (Italy) in 2014. The model does not consider damages to basements. -Carisi_sqrtmono (Carisi et al. 2018) is an empirical uni-variable model, calibrated on the previously cited 2014 Secchia flood event. The model supplies the relative damage to the building (using the market value to relativize the observed monetary damage), as a function of the maximum water depth h (m). The model doesn't consider basements or garages, for coherence with the calibration context. The above models have been applied starting from common data available in the study area (see sect. 3). The results have been compared first among models and then versus the observed losses.
	basement is not considered (Thieken et al. 2008).
	The model is empirically derived from data
	collected from 1697 households affected by the

severe flooding of the rivers Elbe, Danube and some of their tributaries in August 2002 in Germany. -The model by Fuchs et al. (2019) is a simple model considering flow depth only. It is a function developed for mountain areas, i.e. referring

Table 1 .

 1 Pearson correlation coefficient for exposure estimates supplied by the models. ) and building footprint area (m 2 ). The damage models developed for Italian contexts (INSYDE; Arrighi et al. 2018 and Secchia by Carisi et al., 2018) and CEPRI model are those providing the best estimation of the overall amount of monetary damage, although these models yield quite different results in terms of unitary damage except for INSYDE and Secchia MV which give both 85 €/m 2 .

		Arrighi et al.	Dutta, Fuchs	Jonkman	FLEMO-ps	INSYDE	Carisi	sqrtmono &	MV
	Arrighi et al.	1	0.87	0.96 0.97	0.98
	Dutta, Fuchs, Jonkman		1		0.94 0.91	0.92
	FLEMO-ps				1	0.99	0.99
	INSYDE					1	0.98
	Carisi
	sqrtmono &							1
	MV)
	Less correlation is observed in monetary losses, since
	modelling approaches have several assumptions and differ
	in the shape of the damage functions and in the number of
	representative variables. For more details please refer to
	Molinari et al. (2020).
	Table 2 shows a comparison between observed overall
	monetary losses and model estimates as well as the mean
	unitary monetary damage, i.e. the average ratio between
	loss (€

Table 2 .

 2 Observed losses versus monetary estimates with models.


Imen Hammadi

Mohamed Chniter

Marwa Brahmi

Moufida Atigui

Mohamed Dhia Bouzaida

Mouldi-Mabrouk Seddik

Raymond Nowak

Gustavo Adolfo María

Mohamed Hammadi

Mohamed Dhia Bouzaida

Mismothering and remedying the mother-young relationship in stabled dromedary camels

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Camel husbandry is currently evolving from a pastoral towards to an intensive system, due to a selection process for the use of this species in meat and milk production [START_REF] Faye | The camel, new challenges for a sustainable development[END_REF]. Captivity in intensive systems affects locomotion and social activities, limits the expression of various behavioural needs and causes the expression of abnormal behaviours in male camels [START_REF] Padalino | Could Dromedary Camels Develop Stereotypy? The first description of stereotypical behaviour in housed male dromedary camels and how it is affected by different management systems[END_REF]; indoor living conditions could also affect female behaviour especially around parturition.

Giving birth and providing maternal care during the early postpartum period are an essential and critical part of animal breeding management. Ruminants usually isolate from the herd when ready to give birth, an adaptive process that allow the females to give birth in a calm environment away from threats and social disturbances. In normal parturition, the mother turns toward her neonate soon after giving birth and interacts closely with it. Normal maternal responsiveness is characterized by sniffing, nursing and vocalizing activities (sheep and goats: [START_REF] Poindron | Maternal responsiveness and maternal selectivity in domestic sheep and goats: the two facets of maternal attachment[END_REF]cattle: Rørvang et al., 2018, camels: Hammadi et al., 2021). Licking the neonate is also common except in camels [START_REF] Hammadi | Dam parity and calf sex affect maternal and neonatal behaviors during the first week postpartum in stabled Maghrebi dairy camels[END_REF]. Mutual mother-young recognition develops at an early stage and ensures selective suckling and care of the newborn; this satisfies basic requirements such as food, warmth, and protection for its welfare and ensures that the mother does not misspend time and energy in alien young. Consequently, it is acknowledged that the survival of the young ruminant relies, by in large, on appropriate care and selective mother-young bonding [START_REF] Nowak | Role of motheryoung interactions in the survival of offspring in domestic mammals[END_REF][START_REF] Dwyer | A review of the behavioural and physiological adaptations of hill and lowland breeds of sheep that favour lamb survival[END_REF].

Studies in cattle have shown that intensive management systems, involving restricted space and high stocking densities, increase the risk of behavioural disturbances and mismothering during the peripartum period, with failure to provide adequate amount of colostrum to the neonate [START_REF] Rørvang | Pre-partum maternal behavior of domesticated cattle: A comparison with managed, feral, and wild ungulates[END_REF]. Should a newborn calf be abandoned by its mother, even temporarily, nutritional and behavioural needs are not met, and its survival is at risk [START_REF] Vogels | Failure of transfer of passive immunity and agammaglobulinaemia in calves in south-west Victorian dairy herds: prevalence and risk factors[END_REF]. While inadequate maternal care and rejection behaviours have been well investigated in cattle, sheep, goats, and mares [START_REF] Poindron | Maternal responsiveness and maternal selectivity in domestic sheep and goats: the two facets of maternal attachment[END_REF][START_REF] Żurek | Foal rejectioncharacteristics and therapy of inadequate maternal behaviour in mares[END_REF][START_REF] Kohari | Questionnaire investigation to clarify the occurrence rate and characteristics of maternal rejection behavior in Japanese black cattle (Bos taurus)[END_REF], this aspect has never, to date, been investigated in dromedary camels. Research is needed to understand camel postpartum behaviour and the reasons leading to the potential rejection of newborns. Should this happen, it is important to develop practical solution to remedy mismothering. Like other ruminants, newborn camels are agammaglobulinemic, so colostrum is the main source of food and early protective antibodies [START_REF] Salhi | Passive transfer of maternal immunity in the dromedary (Camelus dromedarius), involvement of heavy chain antibodies[END_REF]. Any delay in colostrum ingestion due to inadequate maternal care may be fatal. One potential solution is to confine rejecting mothers in a pen and force them to maintain proximity with their offspring repetitively. This has proven being efficient in sheep for reestablishing proper mother-young relationships [START_REF] Alexander | Fostering in sheep. IV. Use of restraint[END_REF].

Other procedures to remedy altered maternal behaviour in ruminants have been described. In a study by Levey et al. (1992), primiparous ewes prevented from becoming maternal at birth using an epidural anaesthetic block, oxytocin treatment was also effective in inducing full maternal responsiveness. In Tunisian traditional system, the camel breeders restrain the mismothering dam with her neonate far from the rest of the herd. Then, they obstruct the vulva after putting small stones into the vagina and partially block the normal respiration. Even if she-camel accepts her newborn after 3 to 4 hours, these practices are contrasts with ethics and animal welfare. [START_REF] Dioli | The Traditional Management of the One-Humped Camel in the Horn of Africa: Milking, Fostering and Weaning Techniques[END_REF] described rather unusual technique by the Somali and neighboring ethnic groups to treat camel's newborn rejection. This technique included isolating the newly partum camel and her calf than mimicking the behaviour and sound of predators usually at sunset or early night. Soon after she camel reacts to protect the calf, the impersonate retreats. Few nights with this deceit are sufficient to establish maternal-young bond [START_REF] Dioli | The Traditional Management of the One-Humped Camel in the Horn of Africa: Milking, Fostering and Weaning Techniques[END_REF].

Alterations in maternal responsiveness are triggered by stress, because the process of parturition itself is stressful or because the environment does not comply with the behavioural needs of the individual. Behavioural and physiological responses observed in disturbed animals reflect their emotional reactivity [START_REF] Deiss | Can emotional reactivity predict stress responses at slaughter in sheep?[END_REF].

Cortisol, which is considered as an indicator of stress, is also used to predict the time of parturition in female dromedary camels [START_REF] Abd-El-Rahman | Hormonal profile, antioxidant status and some biochemical parameters during pregnancy and periparturient period in dromedary she camel[END_REF].

Foetal cortisol and thyroid hormones play an important role in the maturation and development of the young [START_REF] Liggins | The role of cortisol in preparing the fetus for birth[END_REF]. The decrease of the prepartum cortisol surge in sheep for example reveals a dual mechanism. Firstly, late pregnancy is associated with a rise in cortisol levels being the highest in the last 1-2 days of uterine life, as it is the activation of the hypothalamic-pituitary-adrenal function that is responsible for the birth process [START_REF] Challis | Maturation and activation ofhypothalamicpituitary-adrenal function in fetal sheep[END_REF]. Secondly, the decline in cortisol concurs with periods during which thyroid hormones increase as thermal efficiency improves and rectal temperature stabilizes [START_REF] Chniter | Physiological changes in the peri-partum period and colostral IgG transfer in prolific D'man sheep: effects of parity and litter size[END_REF].

During parturition cortisol levels increase from basal levels at around 21.9 ± 1.0 ng/ml to more than 121.6 ± 5.4 ng/ml [START_REF] Mohamed | Factors affecting cortisol status in camels (Camelus Dromedarius)[END_REF]. This suggests that cortisol may also be used as an indicator of postpartum stress and could be linked to the expression of proper or inadequate maternal responsiveness.

The purpose of this study was twofold. First, we described mismothering behaviours in a herd of stabled dromedary camels, assessed its importance, and identified the causes of calf rejection. Plasma cortisol was also used as a physiological index that would relate to mismothering. Second, we designed a suitable method to try and solve this issue, based on restrain, forced body contact while bottle-feeding the neonate, and food-reward when the mother displayed signs of acceptance.

Material and methods

Animals and housing

The study was conducted at the experimental station of the "Institut des Régions Arides de Médenine", located in southeastern Tunisia (33° 30 ′ N, 10° 40 ′ E), with a typical Mediterranean climate. The work was conducted during two consecutive calving seasons (1 st season: November 2016-March 2017 and 2 nd season: November 2017-April 2018) on respectively 36 (10 primiparas and 26 multiparas) pregnant dromedary females (weighing 440.0 ± 38.0 kg, aged 12.7 ± 5.7 years) and 9 (3 primiparas and 6 multiparas) pregnant dromedary females (weighing 446.0 ± 73.0 kg, aged 14.0 ± 6.2 years). During these two seasons, a total of 6 shecamels showed signs of calf rejection (mother moving more than 2 m away from her newborn just after giving birth) and were assigned to the group of mismothering dams (rejecting group). Whenever a rejection case was recorded, the first following calving with a successful mother-young relationship was also recorded to serve as a control (accepting group). The two mothers group had the same housing conditions. Subsequently, after the first hour postpartum, the mothers accepting their neonates were moved to a maternity enclosure (15 m²), while those rejecting their calves were moved to a confinement enclosure (15 m²) located 200 m from the rest of the herd, to remediate the dam-young bond. The calving pen, feeding and management procedures of the same experimental herd were described previously by [START_REF] Hammadi | Dam parity and calf sex affect maternal and neonatal behaviors during the first week postpartum in stabled Maghrebi dairy camels[END_REF].

Behavioural measurements

Digital infrared video cameras (DAHUA -HAC-HDW1220M) were mounted above the calving pen and used to determine calving behaviours from the appearance of the amniotic sac to the total expulsion of the calf. A qualified person was present during the parturition process to detect and describe the incidence of potential complication (dystocia, uterine prolapse, retained placenta, inappropriate maternal behaviour…) and/or disturbance occurred (presence of alien calves…). Maternal behaviours during the 1 st hour post-calving (sniffing duration and number of low and high-pitched grunts) were measured in the accepting and rejecting groups using a camcorder (Sony® X60). During the first three days postpartum, maternal behaviour was videotaped for the rejecting group in the confinement enclosure over a 30 min period after 1 h, 6 h, 12 h, 24 h, 48 h, 72 h of confinement, however at 7 d postpartum, maternal behaviour was recorded for accepting and rejecting groups. An ethogram was defined to code and measure behaviour traits using the focal-animal sampling method (Altmann,1974) (Table1).

Insert Table 1 here

Cortisol analysis

Once the amniotic sac was visible, a blood sample was taken from the jugular vein into heparinized plain tubes (5 mL). Samples were centrifuged at 3,000 rpm for 15 min at 4°C, and stored at -20°C until hormonal analysis. The concentration of cortisol was determined by enzyme immunoassay using an "in home-kit" (validated by Chacón et al., 2004). Each sample was determined in duplicate from 50 μl of plasma. The mean of the duplicate was used as the result and expressed in µg/ml.

Inter-and intra-assay coefficients of variation were 3.5-6.0% and 3.9-9.9%, respectively.

Remedying the mother-young relationship

Confinement of mothers rejecting their calves

To ensure adoption of abandoned calves, each dam showing mismothering behaviour was isolated with her neonate in an individual enclosure away from the herd and restrained. Because rejecting she-camels can be quite aggressive (Photos 1A, 1B and 1C), we used a multiple procedure to prevent any injury to the young and consisting of:

 Restraining the mother with a 1.5 m of a strong rope in her front leg.

 Using a muzzle mouth guard on the mother to prevent her from biting the newborn and take it off only in her feeding times. At this time, a qualified person surveyed the mother to prevent her from attacking the newborn when approached.

 Tying the mother's front and back legs together with a 1 m rope to prevent her from kicking the newborn.

 Hanging up a thin rope onto the hoofs of the mother once she expressed aggression, and removing it when she showed some nursing behaviour.

 Encouraging the calf to suckle at the udder.

 Providing an extra amount of concentrate food whenever nursing behaviour was observed.

Oxytocin treatment, milking and newborn feeding

Once the mother was moved into the confinement enclosure, 5 IU of synthetic oxytocin (Biocytocine, Laboratoires Biové, Arques, France) were injected into the jugular vein. A qualified person collected an amount of 300 ml of colostrum from the dam and ensured her newborn was fed using a baby bottle held on the surface of the udder and keeping the body contact between the two animals (Photo 1D). This intervention was repeated three times per day (8:00, 12:00 and 16:00) until the mother stopped being aggressive and accepted her neonate.

Statistical analyses

Boris software 6.3.1 [START_REF] Friard | BORIS: a free, versatile open-source event-logging software for video/audio coding and live observations[END_REF] The unpaired t test was used to compare plasma cortisol levels during parturition between accepting and rejecting mothers. Results are presented as means ± standard errors (SEM) and P-values less than 0.05 were considered as statistically significant.

Results

Calving behaviour and cortisol levels in mothers accepting or rejecting their newborns

Calving behaviours

The proportion of females rejecting their newborns was 5/36 during the 1 st and 1/9 females for the 2 nd calving seasons, representing 13.3% of the herd. The duration of parturition was longer in the mothers rejecting their calves compared to those accepting them (Mann-Whitney U = 7; P = 0.04). Compared to the accepting mothers, those which rejected their neonates spent more time in standing position during calving (Mann-Whitney U = 4; P = 0.01), but there was no significant differences in the time spent lying (Fig. 1).

During parturition, mothers rejecting their calves changed their birth place (Mann-Whitney U = 1; P = 0.003) and turned the head towards their abdomen more frequently (Mann-Whitney U = 3; P = 0.007) than those accepting their calves. There was no difference between the two groups in changing posture and tail raising behaviour (Fig. 1). Five out six rejecting females adopted the standing position during the expulsion process and two kicked strongly backwards with their hind legs while this behaviour was never observed in mothers accepting their neonates.

Insert Fig. 1 here

Plasma cortisol level

Mothers abandoning their newborns had higher plasma concentrations of cortisol at parturition than those accepting their newborns (47.7 ± 2.0 vs. 29.5 ± 3.0 ng/ml; respectively, P < 0.01).

Causes of newborn rejection

In our study, the main reasons for abandonment were problems during parturition and the presence of an alien calf (Table 2). The main cause of rejection was found in the birth process (three occurrences). Two females had a long duration of parturition compared to normal calving associated with more discomfort and pain, suggesting dystocia. The third case of mother rejection was associated with dystocia and uterine prolapse in which the uterus protrudes out of the vagina. It required the intervention of the institutional veterinarian who replaced the uterus into its normal position and provided appropriate medical treatment. Only one rejection event was observed in the presence of an alien calf in the calving pen, in which the she-camel displayed maternal response prior to parturition and adopted the alien calf, which lead the mother to reject her own neonate. We hypothesize that the presence of the alien calf is the responsible of this mismothering case. The last case concerned a repeated rejecter, a female that never accepted her newborn in eight successive parturitions. No particular sign of complication during calving was witnessed in this dam.

Insert Table 2 here

Maternal behaviour

Behaviour during the first hour postpartum

Just after giving birth, the accepting mothers stayed close to their neonates and provided care by protecting them between their front legs. During the first hour postpartum, mothers rejecting their neonates exhibited less sniffing (both duration and number), emitted less low and high-pitched grunts than those accepting their neonates, and failed to show proper maternal care (Table 3). In addition, they were indifferent to and moved away from their progeny. The mother who suffered from dystocia and uterus prolapse was unable to get up and remained near her calf without any responsiveness.

Insert Table 3 here

Behavioural progress in mothers rejecting newborns

In the confinement enclosure, the calves approached to suckle their mothers, but they displayed attack behaviours in response and refused to nurse (Photos 1A, 1B and 1C). The number of these behaviours was the highest in the first 6 h before declining significantly (Kruskal-Wallis = 32.4; P < 0.0001) after one day and disappearing almost completely after 3 days of confinement (Fig. 2A). The reverse is observed in the sniffing activity, which was limited in the first day. Then, both the duration (Kruskal-Wallis = 21.7; P = 0.001; Fig. 2B) and the number of sniffing bouts (Kruskal-Wallis = 22.0; P = 0.001; Fig. 2C) increased significantly in the following days.

The number of high-pitched grunt was high during the first hour of confinement, dropped after 12 hours and then remained at a low level (Kruskal-Wallis = 29.4; P < 0.0001; Fig. 3A). By contrast, the number of low-pitched grunt started low (Kruskal-Wallis = 21.4; P =0.001; Fig. 3B) and increased progressively over the first 3 days of confinement before declining significantly on the 7 th day.

Insert Figures 2 and 3 here

Progressively, mothers accepted the presence of their newborns without any aggressive reactions. The next step was acceptance of the calf's attempts to make body contact without paying any particular attention to it or exhibiting any maternal care. This was facilitated by the human positioning the calf into normal suckling posture when giving colostrum and milk through a bottle (Photo 1D and 1E). The final step was total acceptance of the rejected calf with remediation of the mother-young relationship and complete restoration of maternal behaviour (Photos 1F and 1G).

Insert Photos 1 here

Maternal behavioural in mothers accepting and rejecting newborns at the 7 th day postpartum

After returning to the herd, and at day 7 postpartum rejecting mothers exhibited more low-pitched grunts (Mann-Whitney U = 0; P = 0.001) and sniffing bouts (Mann-Whitney U = 2; P = 0.005) compared to the accepting mothers. However, there was no difference in the high-pitched grunts (P = 0.45) and in sniffing duration (P = 0.13) between the two mother's group (Fig. 4).

Insert Figure 4 here

Discussion

Newborn camel rejection by mothers had never been described before the present work. Despite the limited sample size, and the luck of comparison with other methods to remediate mismothering, this study provides an applied technique to reduce mismothering and to remediate this problem of rejection in the camel.

Aberrant maternal behaviour was related to birth difficulties with dystocia and uterine prolapse in three cases, rejection of the neonate in two occurrences, while acceptance of an alien calf prior to giving birth was observed only once. It is a phenomenon that should not be neglected since it affected 13% of the herd. This aberrant behaviour is reversible and mothers needed 3 days of restrain and human assistance to maintain contact with the calf and restore signs of acceptance. One striking element is that mismothering was displayed by multiparous camels, while in domestic ungulates such behaviour characterizes inexperienced primiparous mothers (Dweyer and Smith, 2008;McDonnell, 2012;Lv et al., 2015).Ihuthia (2010) reported rather frequent newborn abandon by multiparous camels. He reported that up to 27.5% of abandon cases were registered in experienced camels. Some mares, almost always primiparous, react to their neonate with fear behavior as they react to objects which they have not been exposed. Positive reinforcement is effective in helping a horse overcome fear of her newborn (McDonnell, 2012). In sheep and horses, there is some speculation that in addition to environmental factors, maternal rejection might also have a genetic background and may make an animal more likely to reject the offspring repeatedly [START_REF] Juarbe-Diaz | Prevalence and characteristics of foal rejection in Arabian mares[END_REF][START_REF] Grandinson | Genetic background of maternal behaviour and its relation to offspring survival[END_REF]. However, hormonal failure during post-partum could also explain repeated calf rejection in our camels. In fact, it has been reported that in ewes, females with better maternal behavior have a higher level of oxytocin and noradrenaline than mismothering ones (Wang et al., 2021).

In our study, the duration of parturition was longer in dromedary females that rejected their calves compared to those accepting them. That parturition is a source of discomfort is unquestionable and maybe even more in mammals giving birth to a reduced number of newborns, especially singletons because of their size. Parturient cows become quite agitated immediately before parturition, and in sheep the incidence of prolonged and difficult parturition is threefold higher in single-bearing ewes (Grommer et al., 1985;[START_REF] Keyserlingk | Maternal behavior in cattle[END_REF]. This can impair the mother's motivation to care for her offspring [START_REF] Nowak | Role of motheryoung interactions in the survival of offspring in domestic mammals[END_REF]. Prolonged and difficult parturition, assigned to pain and discomfort, is associated with reduced mothering behaviour in ewes and mares, and contributes to increase newborn rejection [START_REF] Dwyer | Ewe-lamb bonding behaviours at birth are affected by maternal under nutrition in pregnancy[END_REF][START_REF] Żurek | Foal rejectioncharacteristics and therapy of inadequate maternal behaviour in mares[END_REF].

Three typical signs of uneasiness were observed in camels: head-turning towards the abdomen, regular changes of birth site, and standing position. Close to parturition, females start to behave unusually, and restlessness is part of it. In some species like cattle, restlessness is associated with frequent orientation of the head towards the abdomen and reflects imminent calving [START_REF] Barrier | Effect of difficult calving on the vigour of the calf, the onset of maternal behaviour, and some behavioural indicators of pain in the dam[END_REF]. It is considered as a sign of disturbance since this behaviour is observed more frequently in mothers needing assistance [START_REF] Mainau | Effect of time and parity on the behaviour of dairy cows during the puerperal period[END_REF]. In this regard, camels are very similar to cattle. Isolation seeking and selecting a birth site is another general trend in domestic ungulates [START_REF] Jensen | The Ethology of Domestic Animals. 3 rd Edition. An Introductory Text[END_REF], a behaviour that cannot be achieved under intensive conditions. The constraints imposed on stabled camels may disturb the future mother in her choice of birthplace, prolong labor, and impair the behavioural changes necessary for the onset of maternal motivation as already described in stabled animals [START_REF] Grandinson | Genetic background of maternal behaviour and its relation to offspring survival[END_REF][START_REF] Nowak | From birth to colostrum: early steps leading to lamb survival[END_REF]. It has been shown in sheep reared under intensive conditions, that should cubicles be provided for isolation, periparturient ewes use them actively, and when doing so they spend less time moving around and are less likely to be separated from their lambs [START_REF] Gonyou | Behavior of parturient ewes in group-lambing pens with and without cubicles[END_REF]. In our experiment, she-camels that displayed mismothering changed birth site more frequently than those that accepted their calves. Likewise, studies in sheep have shown that twin-bearing ewes are more likely to desert one of their lambs if they have been moved away from the birth site [START_REF] Nowak | Neonatal survival: Contributions from behavioural studies in sheep[END_REF]. Selecting and staying on the birth site is crucial for the development of mother-young interaction and bonding. Adequate space and facilities with minimal provocation of protective behavior are recommended until protectiveness period naturally diminish.

Restlessness was also associated in she-camels with more frequent standing posture during the expulsion process, and sometimes kicking. This reflects intense discomfort as reported in cows [START_REF] Norman | Parturition and Dystocia[END_REF] or in primiparous she-camels [START_REF] Hammadi | Dam parity and calf sex affect maternal and neonatal behaviors during the first week postpartum in stabled Maghrebi dairy camels[END_REF]. In addition, rejecting mothers preferred the standing position during calving, which is not the normal posture adopted by dromedary camels as documented recently by [START_REF] Hammadi | Dam parity and calf sex affect maternal and neonatal behaviors during the first week postpartum in stabled Maghrebi dairy camels[END_REF]. Lateral recumbency is in fact a general trend in domestic ungulates. Whether birth difficulties were directly responsible for increased locomotion and aberrant postures or due to the emotional reactivity of some females that were stressed by the indoor rearing conditions is unknown and should deserve further attention.

In any case, plasma cortisol concentration was shown to be higher in shecamels that expressed mismothering. In ungulates, cortisol levels typically increase with labor and rise during expulsion of the fetus [START_REF] Nagel | Stress effects on the regulation of parturition in different domestic animal species[END_REF]. [START_REF] Agarwal | Studies on postpartum female camels and their neonates[END_REF] reported a periparturient concentration around 25 -30 ng/ml in camels which is considered to be important. While high concentrations around calving may arise from the need for glucocorticoids increased to induce lactation, the metabolic clearance rate reduced by estrogens and the onset of parturition trigged by fetal maturation, abnormal parturition exacerbates such response [START_REF] Sathya | Vitamin E and selenium supplementation reduces plasma cortisol and oxidative stress in dystocia-affected buffaloes[END_REF].

Our results confirmed these findings and show that cortisol, birth difficulties and mismothering were related.

Under overcrowded conditions, stealing other neonates is common in domestic ungulates and has deleterious consequences with mothers accepting alien young but rejecting their own [START_REF] Owens | Parturient behaviour and calf survival in a herd selected for twinning[END_REF]. It is particularly the case when two females give birth at the same time because the amniotic fluids are attractive around birth, determine the choice of birth site once spilt on the ground, and trigger maternal licking [START_REF] Nowak | From birth to colostrum: early steps leading to lamb survival[END_REF][START_REF] Poindron | Maternal responsiveness and maternal selectivity in domestic sheep and goats: the two facets of maternal attachment[END_REF]. This was observed only once in our she-camels. We cannot conclude whether the scarcity of such behaviour was due to the fact that camels, unlike other ruminants, do not lick their young after giving birth [START_REF] Hammadi | Dam parity and calf sex affect maternal and neonatal behaviors during the first week postpartum in stabled Maghrebi dairy camels[END_REF] or because calving was scattered over several months, making stealing of newborns unlikely to happen.

In Maghrebi dromedary camels, an intense period of behavioural interactions between the mother and her newborn usually takes place after birth during which sniffing and low-pitched grunt characterize maternal responsiveness [START_REF] Hammadi | Dam parity and calf sex affect maternal and neonatal behaviors during the first week postpartum in stabled Maghrebi dairy camels[END_REF]. It is believed that such behaviours are important for promoting bond formation between the mother and her newborn like in sheep and goats [START_REF] Grandinson | Genetic background of maternal behaviour and its relation to offspring survival[END_REF][START_REF] Nowak | From birth to colostrum: early steps leading to lamb survival[END_REF][START_REF] Poindron | Maternal responsiveness and maternal selectivity in domestic sheep and goats: the two facets of maternal attachment[END_REF]. During the first postpartum hour, she-camels displaying birth difficulties failed to show proper maternal care and rejected their young. Unlike those that accepted their neonates, mothers attacked and bit their own if they approached to suckle, hardly smelt them, and emitted highpitched grunt. Newborn rejection is also observed in horses but with a different reaction comparatively to camels, in which mares going to their newborns and attack, squeal, bite, and kick them, leading to injuring them (Zurek and Danek, 2012).

Rejection behaviours in other ungulates like sheep are less severe with head threatening, butting and pushing. Care must be taken in camels to protect the calf by restraining the mother's movement as bites and kicks might be fatal. Calf rejection must be dealt with immediately after being witnessed to have the best chance of solving the issue.

In the present work, the first step to remedy mismothering was to isolate the mother and her abandoned calf in a small yard. The second was to restrain agitation by putting a muzzle on the mother's nose and tying up her legs. Biting and kicking were prevented while the female could still walk around freely. The third stage was to provide colostrum to the calf by milking the mother after an intravenous injection of oxytocin and bottle-feeding the neonate. Finally, human assistance helped the calf to find the teats, maintain contact with the mother, and suckle without being rejected. All these steps were performed by a qualified person who provoked proximal interindividual interactions. By doing so, aggressive behaviours and high-pitched grunt vanished after 2 days of confinement while sniffing and low-pitched grunt were restored. The she-camel began to accept the newborn showing that the motheryoung relationship became satisfactory, and that in all likelihood a bonding process was taking place.

The mechanisms restoring maternal acceptance are unknown but our methods combined two main factors. The first is the use of restraint, a method known to induce fostering in sheep [START_REF] Alexander | Fostering in sheep. IV. Use of restraint[END_REF] since it prevents aggression, promotes close contact, and facilitates nursing. Proximal contact facilitates perception of body odors, and olfactory communication is crucial for the establishment of a bond between mother and offspring in sheep and goats [START_REF] Nowak | From birth to colostrum: early steps leading to lamb survival[END_REF][START_REF] Nowak | From birth to colostrum: early steps leading to lamb survival[END_REF]. Restoring maternal responsiveness with the use of restraint takes several days in sheep and only two days in horses [START_REF] Juarbe-Diaz | Prevalence and characteristics of foal rejection in Arabian mares[END_REF]. Camels fit within that timeframe. The second factor could be oxytocin. Oxytocin has been shown to induce maternal behaviour in a number of mammals including ruminants [START_REF] Kendrick | Oxytocin, motherhood and bonding[END_REF]. It stimulates physical proximity between the mother and young, minimizes rejection of newborns and facilitate nursing (Keverne and Kendrick, 1992). Oxytocin has also been found to reduce aggression towards offspring and to decrease the level of fearfulness. The injection of exogenous Biocytocine® prior to milking, milking itself and nursing -which are known to trigger the release of central oxytocin -might have facilitated the onset of maternal responsiveness in rejecting she-camels.

Conclusion

In conclusion, breeders of stabled dromedary camels should be able to deal with mismothering immediately after calving. Reserving a special calving pen may be essential for each periparturient mother to avoid newborn rejection and calf stealing by alien females. An isolated confinement enclosure is necessary to remediate the mother-young relationship and encourage maternal care. Our study showed that dromedary females that rejected their newborns needed 3 days of restrain and human assistance to accept their calves correctly. This work describes some aspects relating to abnormal maternal behaviour but does not cover all of the issues. There are still many aspects to be clarified. One striking element is that mismothering was displayed by multiparous camels, while in domestic ungulates such behaviour characterizes inexperienced primiparous mothers. In sheep and horses, there is for each parameter, difference between groups is significant at P = 0.05. Table 1 Ethogram of calving and maternal behaviour in Maghrebi dromedary camels (adopted with some modifications from [START_REF] Hammadi | Dam parity and calf sex affect maternal and neonatal behaviors during the first week postpartum in stabled Maghrebi dairy camels[END_REF].

Variable

  was used to analyze behavioural data. Statistical analyses were performed with GraphPad Prism 7.00 for Windows (2016). Test of normality (Shapiro-Wilk test) was performed and showed a non-normal distribution. Consequently, comparison between the two mothers group on maternal expression during calving (change in birth site, head-turning, changing posture, tail raising, posture during newborn expulsion and newborn attack), and maternal behaviours (sniffing duration and number and low and high-pitched grunts) during the 1 st hour and the 7 th day postpartum were performed using the Mann-Whitney test. Overall, the effect of time (1 h, 6 h, 12 h, 24 h, 48 h, 72 h of confinement and 7 d postpartum) on maternal behaviors was performed by Kruskal-Wallis test with Dunn's correction for multiple comparisons. P-values less than 0.05 were considered as statistically significant. Results are presented in terms of median and lower and upper quartiles [LQ-HQ].

Fig. 1 .

 1 Fig. 1. Parturition, lying and standing duration (A), number of changing posture, changing place; head turning towards abdomen and tail raising (B) during the calving process in dromedary mothers accepting (accepting group) and rejecting (rejecting group) their calves. Data are expressed as medians and 1st and 3rd quartiles. a-b:

Fig. 2 .

 2 Fig. 2. Evolution of newborn, number of attack (A), and duration (B) and number (C) of sniffing in dromedary females that rejected their calves during the confinement period and at day 7 postpartum. Data are expressed as medians and 1 st and 3 rd quartiles. a-b-c: P < 0.05.

Fig. 3 .

 3 Fig. 3. Evolution of number of high (A) and low-pitched grunts (B) in the rejecting group during the confinement period and at day 7 postpartum. Data are expressed as medians and 1 st and 3 rd quartiles. a-b: P < 0.05.

Fig. 4 .

 4 Fig. 4. Difference between the accepting and rejecting groups in low-pitched grunt (A), high-pitched grunt (B), number of sniffing (C) and sniffing duration (D) at day 7 postpartum. Data are expressed as medians and 1 st and 3 rd quartiles. a-b: for each parameter, difference between groups is significant at P = 0.05.

Fig

  Fig. 1.

  Fig. 3.

  Photos 1: Steps in calf acceptance during the confinement period in dromedary camels.A: attacking the calf; B: biting the calf; C: refusing suckling; D: colostrum collection from the mother and Bottle-feeding the calf near to the udder; E: mother accepts body contact; F: suckling acceptance without maternal care; G: suckling process with maternal care (sniffing).

Acknowledgements

The present work was carried out in the "Laboratoire d'Elevage et Faune Sauvage (LR16IRA04) at the Institut des Régions Arides de Médenine". It was funded by the Ministère de l'Enseignement Supérieur et de la Recherche Scientifique. Our gratitude to the farm staff of the "Laboratoire d'Elevage et Faune Sauvage" for their care of the animals and their invaluable assistance. The authors would like also to express their deep appreciation to the staff of the "Faculty of Veterinary Medicine University of Zaragoza, Spain" for their help in the cortisol analyses.

some speculation that in addition to environmental factors, maternal rejection might also have a genetic background and may make an animal more likely to reject the offspring [START_REF] Juarbe-Diaz | Prevalence and characteristics of foal rejection in Arabian mares[END_REF][START_REF] Grandinson | Genetic background of maternal behaviour and its relation to offspring survival[END_REF]. The factors involved in this phenomenon are yet to be identified. No doubt there is great scope for future research in maternal behaviour in the camel.

Declaration of interest

The authors declare that they have no conflicts of interest.

Ethics statement

The experimental conditions of the present work complied with the European Directive 2010/63/EU on the protection of animals used for scientific purposes.