Claude Miaud

Guillaume Testud

Clément Fauconnier

Dorothée Labarraque

Thierry Lengagne

Quentin Lepetitcorps

Damien Picard

Acoustic enrichment in wildlife passages under railways improves their 2 use by amphibians Access 3

Keywords: Transport infrastructure, Tunnels, Mitigation evaluation, Acoustic orientation Triturus marmoratus, alpine newt Ichthyosaura alpestris, fire salamander Salamandra 24 Transport infrastructure, Tunnels, Mitigation evaluation, Acoustic 12 43 orientation

Linear transport infrastructure can impact wildlife directly or indirectly, and 16 amphibians are particularly affected. In some cases, mitigation measures -such as 17 tunnels below the linear transport infrastructure -are implemented, but an 2 18 evaluation of their effectiveness is often lacking, especially for small animals such as 19 amphibians. Few studies have focused on crossing behaviour in underpasses, yet this 20 information may be crucial to improve mitigation measures. In this study, we 21 conducted experiments in three tunnels below a high-speed railway with 40 41 22 individually marked amphibians (great crested newt Triturus cristatus, marbled newt 23

tract:

Linear transport infrastructure can impact wildlife directly or indirectly, and amphibians are particularly affected. In some cases, mitigation measuressuch as tunnels below the linear transport infrastructureare implemented, but an evaluation of their effectiveness is often lacking, especially for small animals such as amphibians. Few studies have focused on crossing behaviour in underpasses, yet this information may be crucial to improve mitigation measures. In this study, we conducted experiments in three tunnels below a high-speed railway with individually marked amphibians (great crested newt Triturus cristatus , marbled newt Triturus marmoratus , alpine newt Ichthyosaura alpestris , fire salamander Salamandra salamandra , spined toad Bufo spinosus , agile frog Rana dalmatina and edible/pool frog Pelophylax kl. esculentus/lessonae ) which were released at the entrance of tunnels varying in length. Behaviours (e.g. completed crossing, U-turn, not moving, and stay) and crossing speed were recorded. R. dalmatina , S. salamandra and T. cristatus (but not B. spinosus ) exhibited crossing rate differences between tunnels 21 m and 40 m in length. More individuals performed "complete crossing" through the shorter tunnel. The crossing speed of the S. Salamandra and T. cristatus did not differ between the tunnels of different lengths. In a second experiment, we evaluated the effect of acoustic enrichment on the crossing behaviour of one frog and three newt species by broadcasting a soundtrack of mating calls of syntopic anuran species in the tunnels. P. kl esculentus/lessonae exhibited a large increase in complete crossings and in speed. T. cristatus showed an increase in tunnel complete crossings (but not speed) in one of the acoustically enhanced tunnels.

These results indicate that acoustic enrichment can improve the crossing of underpasses. This low cost and easily implementable method could help to inform the design of wildlife passages as mitigation measures for impacted amphibian populations, though more experiments on the effect of tunnel characteristics on amphibian behaviour would be valuable.

tunnels of different lengths. In a second experiment, we evaluated the effect of 32 acoustic enrichment on the crossing behaviour of one frog and three newt species by 33 broadcasting a soundtrack of mating calls of syntopic anuran species in the tunnels.

34

Pelophylax kl exhibited a large increase in complete crossings and in speed. T. cristatus 35 showed an increase in tunnel complete crossings (but not speed) in one of the 36 acoustically enhanced tunnels. These results indicate that acoustic enrichment can 37 improve the crossing of underpasses. This low cost and easily implementable

Introduction 48

Global passenger and freight travel is expected to double from its level in 2010 in 49 coming decades, and it is projected that around the world an additional 25 million 11 50 kilometres of paved roads and 335,000 kilometres of railway tracks will be needed 14 51 [START_REF] Dulac | Global land transport infrastructure requirements -Estimating road and railway infrastructure 497 capacity and costs to 2050 -UCSTUDI[END_REF]. The effects of linear transport infrastructure (LTI) such as roads and 17 52 railways on animals have long been known [START_REF] Barbour | Bird fatality along Nebraska railroads[END_REF] and have been 20 53 extensively studied (e.g. [START_REF] Rytwinski | The impacts of roads and traffic on terrestrial animal populations[END_REF]. The construction of LTI in surface as well as its connectivity, impacting animals through direct mortality and 56 behaviour changes in land use and movements [START_REF] Jackson | A strategy for mitigating highway impacts on wildlife. Wildlife and highways: 518 seeking solutions to an ecological and socio-economic Dilemma[END_REF] 31 57 [START_REF] Trombulak | Review of ecological effects of roads on terrestrial and aquatic 585 communities[END_REF]. The resulting decrease in population size, landscape 34 58 connectivity and dispersal can significantly alter the viability of populations 37 59 [START_REF] Eigenbrod | The relative effects of road traffic and forest cover on anuran 499 populations[END_REF][START_REF] Forman | Roads and Their Major Ecological Effects[END_REF][START_REF] Glista | A review of mitigation measures for reducing wildlife mortality 507 on roadways[END_REF]Hamer et al., 40 60 2014; [START_REF] Lesbarrères | Measures to reduce population fragmentation by roads: what has worked and 535 how do we know?[END_REF]. [START_REF] Joly | Behavior in a changing landscape: Using movement ecology to inform the conservation of pond-526 breeding amphibians[END_REF][START_REF] Ronce | How does it feel to be like a rolling stone? Ten questions about dispersal evolution[END_REF]. As a consequence, it is not surprising 66 that amphibians, which have a biphasic lifecycle (terrestrial and aquatic), are one of 67 the groups most affected by landscape fragmentation [START_REF] Beebee | Effects of road mortality and mitigation measures on amphibian populations[END_REF][START_REF] Cushman | Effects of habitat loss and fragmentation on amphibians: A review and prospectus[END_REF] 68 [START_REF] Holderegger | The genetic effects of roads: A review of empirical evidence[END_REF].

69

Wildlife passages constructed for small vertebrates (often tunnels below railway 70 tracks) aim to reduce the barrier effect and thus its alteration of population 71 functioning [START_REF] Beebee | Effects of road mortality and mitigation measures on amphibian populations[END_REF][START_REF] Clevenger | Wildlife crossing structures, fencing, and other highway design considerations[END_REF]Colino-Rabanal and Lizana, 72 2012; [START_REF] Dodd | Effectiveness of a barrier wall and culverts in reducing wildlife 493 mortality on a heavily traveled highway in Florida[END_REF][START_REF] Hamer | Usage rates of an under-road tunnel by three 21 509 Australian frog species: implications for road mitigation[END_REF][START_REF] Jarvis | Road mitigation using tunnels and fences promotes site 523 connectivity and population expansion for a protected amphibian[END_REF]. However, while 73 evaluating the effectiveness of these structures for different species is crucial (Jarvis 74 et al., 2019;[START_REF] Lesbarrères | Measures to reduce population fragmentation by roads: what has worked and 535 how do we know?[END_REF], amphibian behaviour near and inside the 75 tunnels is rarely investigated (Matos et al., 2018;[START_REF] Testud | From effects of linear transport infrastructures on amphibians to mitigation 578 measures[END_REF]. Some 76 experiments have tested abiotic tunnel characteristics such as diameter and length 77 [START_REF] Patrick | Effective culvert placement and design to facilitate 552 passage of amphibians across roads[END_REF], substrate [START_REF] Lesbarrères | What type of amphibian tunnel could reduce road kills?[END_REF][START_REF] Trochet | Influence of substrate 40 582 types and morphological traits on movement behavior in a toad and newt species[END_REF], and light, 78 humidity and temperature [START_REF] Bain | Evaluating the effects of abiotic and biotic factors on movement 34 465 through wildlife crossing tunnels during migration of the california tiger salamander, Ambystoma 35 466 californiense[END_REF]. Biotic parameters (e.g. physiological 79 condition of amphibians, vegetation colonization of the tunnels) or social information 80 (e.g. presence of conspecific cues), on the other hand, have been little studied.

81

According to the chorus attraction hypothesis [START_REF] Gerhardt | Acoustic communication in insects and anurans: common problems and diverse 17 505 solutions[END_REF], 82 amphibians may use the calls of conspecifics or other species for orientation (Buxton 83 et al., 2015;[START_REF] Diego-Rasilla | Homing ability and sensitivity to the geomagnetic field in the alpine newt, Triturus 479 alpestris[END_REF]Luengo, 2007, 2004;[START_REF] James | Investigating behaviour for 520 conservation goals: Conspecific call playback can be used to alter amphibian distributions within 521 ponds[END_REF]Madden and 84 Jehle, 2017;[START_REF] Pupin | Discrimination of toad calls by smooth newts: 562 support for the heterospecific attraction hypothesis[END_REF][START_REF] Swanson | Do female frogs exploit inadvertent social information to locate 576 breeding aggregations?[END_REF]. For example, adult of marbled 85 newt Triturus marmoratus orientate to the calls of the natterjack toad Epidalea calamita 86 an experimental arena [START_REF] Diego-Rasilla | Heterospecific call recognition and phonotaxis in the orientation 54 483 behavior of the marbled newt, Triturus marmoratus[END_REF] broadcasting vocalizations [START_REF] Putman | Correction to: What is the effectiveness of using conspecific or 565 heterospecific acoustic playbacks for the attraction of animals for wildlife management? A systematic 566 review protocol[END_REF]. In amphibians, acoustic enrichment with conspecific chorus calls has been shown to improve the colonization of new ponds by frogs and toads [START_REF] Buxton | Use of chorus sounds for location of breeding habitat in 2 species 471 of anuran amphibians[END_REF][START_REF] James | Investigating behaviour for 520 conservation goals: Conspecific call playback can be used to alter amphibian distributions within 521 ponds[END_REF]. These findings suggest that acoustic enrichment might be an interesting avenue to explore to increase the effectiveness of wildlife passages.

The aim of this study was to evaluate the use of wildlife passages by amphibians and investigate methods to improve their effectiveness.

Materials and methods

Study area and wildlife crossing structures

The study area was located in the region of Pays-de-la-Loire in northwestern France.

Our focus was on three wildlife crossing structures constructed at different locations under the same high-speed railway track. Tunnels 1 and 2 are separated by a m. Tunnels 1 and 2 are dry fauna-crossing structures installed for amphibians, while Freeman-Halton test, p-value: 0.6, figure 2f).

239

According to the previous results, individuals (in S. salamandra and T. cristatus)

240
that completely crossed a tunnel allowed estimating a mean crossing speed. In S. 20 241 salamandra adults, the crossing speed did not differ between tunnel 1 and 2 (tunnel 1 242 N = 47; tunnel 2 N = 11, Wilcoxon-Mann-Whitney test, p-value: 0.71, figure 3). This Fisher-Freeman-Halton test, p-value: 0.21, figure 4a). The number of juveniles that 260 completed crossings was too low to calculate the crossing speed (Table 1). In T.

261 cristatus adults (tunnel 1), the proportion of behaviour categories significantly Fisher-Freeman-Halton test, test p-value: 0.45, figure 4e). The number of individuals 278 completely crossing the tunnels was too low to calculate crossing speed (Table 1).

279

In I. alpestris adults (tunnel 3), the proportion of behaviour categories did not 280 differ with or without acoustic enrichment (without N = 36; with N = 30, Fisher-

281

Freeman-Halton test, test p-value: 0.12, figure 4f). The number of individuals 282 completely crossing the tunnels was too low to calculate crossing speed (Table 1).

283

In Pelophylax kl. adults (tunnel 3), the proportion of behaviour categories

Discussion

293

Various studies have demonstrated that linear transport infrastructure strongly alters 294 animal land use behaviour and movements [START_REF] Jackson | A strategy for mitigating highway impacts on wildlife. Wildlife and highways: 518 seeking solutions to an ecological and socio-economic Dilemma[END_REF]Trombulak 295 and Frissell, 2000). When LTI interrupts amphibian migration or dispersal, different 296 mitigation methods have been implemented with varying efficacy (Colino-Rabanal 297 and Lizana, 2012). Wildlife passages constructed specifically for small vertebrates 298 such as amphibians can reduce direct mortality from LTI as well as its barrier effect, 299 contributing to improve population viability [START_REF] Beebee | Effects of road mortality and mitigation measures on amphibian populations[END_REF]Clevenger and Ford, 300 2010; [START_REF] Dodd | Effectiveness of a barrier wall and culverts in reducing wildlife 493 mortality on a heavily traveled highway in Florida[END_REF][START_REF] Hamer | Usage rates of an under-road tunnel by three 21 509 Australian frog species: implications for road mitigation[END_REF][START_REF] Jarvis | Road mitigation using tunnels and fences promotes site 523 connectivity and population expansion for a protected amphibian[END_REF]. However, the 301 effectiveness of these mitigation measures has not been sufficiently assessed (Jarvis et 302 al., 2019;[START_REF] Lesbarrères | What type of amphibian tunnel could reduce road kills?[END_REF][START_REF] Pagnucco | Characterizing movement patterns and spatio549 temporal use of under-road tunnels by long-toed salamanders in Waterton Lakes National Park, 550 Canada[END_REF][START_REF] Puky | Use of existing mitigation measures by amphibians, reptiles, and small 15 559 to medium-size mammals in Hungary: Crossing structures can function as multiple species-oriented 16 560 measures[END_REF]Testud and 25 303 Miaud, 2018;[START_REF] Woltz | Road crossing structures for amphibians and reptiles: Informing 592 design through behavioral analysis[END_REF], especially for European newts [START_REF] Matos | Facilitating permeability of landscapes impacted by roads 543 for protected amphibians: patterns of movement for the great crested newt[END_REF].

304

Evaluating the behaviour of amphibians in tunnels is challenging (see a review 305 in [START_REF] Testud | Automatic detection of small PITtagged 580 animals using wildlife crossings[END_REF]. The lack of behavioural data on small species crossing tunnels 306 is partly due to methodological issues [START_REF] Weber | Testing the applicability of tagging the Great crested newt 47 589 (Triturus cristatus) using passive integrated transponders[END_REF]. For example, camera traps 25 307 are widely used for movement tracking in tunnels (reviewed in [START_REF] Jumeau | Les possibilités de dispersion et éléments d'habitat-refuge dans un paysage d'agriculture 46 532 intensive fragmenté par un réseau routier dense: le cas de la petite faune dans la plaine du Bas-Rhin[END_REF]. The 308 detection rate can be low with amphibians [START_REF] Pagnucco | Characterizing movement patterns and spatio549 temporal use of under-road tunnels by long-toed salamanders in Waterton Lakes National Park, 550 Canada[END_REF], but the current 309 increase in the quality of video traps make them usable with amphibians (Hobbs and 310 Brehme, 2017;[START_REF] Jarvis | Road mitigation using tunnels and fences promotes site 523 connectivity and population expansion for a protected amphibian[END_REF][START_REF] Pomezanski | Developing recommendations for monitoring wildlife underpass usage using 12 556 trail cameras[END_REF]. Marking 311 amphibians with fluorescent pigments was used as a method to record continuous 312 tracks on the tunnel floor, but this method is limited in terms of the number of speed [START_REF] Matos | Short-term movements and behaviour govern the 546 use of road mitigation measures by a protected amphibian[END_REF]. A more promising method is PIT-tagging individuals and 315 tracking their movements with detectors installed in tunnels (Atkinson-Adams, 2015; 316 [START_REF] Testud | Automatic detection of small PITtagged 580 animals using wildlife crossings[END_REF].

317

We used PIT-tagging and based our experiments on the concept of homing 318 behaviour, i.e. the propensity of displaced amphibians to come back to the place of 319 capture [START_REF] Dole | Homing and orientation of displaced toads, Bufo americanus, to their home sites[END_REF][START_REF] Sinsch | Orientation behaviour of toads (Bufo bufo) displaced from the breeding site[END_REF]. We assumed that individuals captured on land 320 while migrating to a breeding place (this was the case for S. salamandra and B.

321 spinosus) were in a suitable physiological condition to evaluate their terrestrial 322 movements in tunnels. In the case of the newts T. cristatus, T. marmoratus and I.

323 alpestris, these were caught in ponds at dates when they were reproductively active.

324

Newts caught in ponds can successfully return to the site of capture from 325 displacement distances of more than 100 m (e.g. [START_REF] Joly | Fidelity to the breeding site in the alpine newt Triturus alpestris[END_REF]Twitty et al., 27 326 1964). In future, it would also be interesting to perform similar homing experiments 327 to evaluate tunnel use with newts caught on land (i.e. before they enter the aquatic 328 phase).

329

Our experimental design raised another issue about movement behaviour. The 330 specimens were released at the entrance of a tunnel every minute. We analysed the 331 data considering each specimen trajectory as independent; however, several 332 individuals (of the same species) were present in the tunnel and could potentially 333 interact. Newts can use specific and heterospecific information (e.g. density) to 334 emigrate from ponds [START_REF] Cayuela | Context-dependent dispersal, public information, and heterospecific 473 attraction in newts[END_REF]. Laboratory experiments showed that 335 juvenile T. cristatus can detect scents left on the substrate by conspecifics (Hayward et 336 al., 2000). However, the use of conspecific cues during migration on land remains 337 unknown. In anurans such as toads, intra-and inter-sexual interactions such as 338 couple forming, can potentially change the movement of migrating adults (e.g.

339

Arntzen, 1999). In our experiments, 4 female and 17 male B. spinosus were tested, but

340
we do not have information on their interactions. Lastly, water frogs, which travel 341 mainly by jumping, could also potentially influence conspecifics when crossing 342 tunnels. Nonetheless, despite the fact that certain complex behavioural interactions 343 may have occurred in the tunnels during the experiments, we can consider that these 344 were similar in all tunnels and tested conditions and so did not bias the comparisons.

345

Studies have tested how tunnel characteristics influence the crossing of 346 amphibians with 'experimental' tunnels (i.e. devices mimicking tunnels implemented 347 below LTIs). Tested characteristics include diameter [START_REF] Patrick | Effective culvert placement and design to facilitate 552 passage of amphibians across roads[END_REF], length 348 [START_REF] Patrick | Effective culvert placement and design to facilitate 552 passage of amphibians across roads[END_REF], substrate [START_REF] Lesbarrères | What type of amphibian tunnel could reduce road kills?[END_REF][START_REF] Trochet | Influence of substrate 40 582 types and morphological traits on movement behavior in a toad and newt species[END_REF], and light, 349 humidity and temperature [START_REF] Bain | Evaluating the effects of abiotic and biotic factors on movement 34 465 through wildlife crossing tunnels during migration of the california tiger salamander, Ambystoma 35 466 californiense[END_REF]. Our study was performed in 'real' 350 tunnels below a high-speed railway track; tunnels whose dimensions differed only in 29 351 length. In experiments with two tunnels (21 m and 40 m long -both 1 m wide and 1 352 m high), the longer length was found to impact the proportion of complete crossings 353 by S. salamandra (from 68% to 34%), adult T. cristatus (from 38% to 14%) and R.

354 dalmatina (from 34% to 0%). No effect of length was observed for B. spinosus, but this 355 result needs to be confirmed with a higher number of tested individuals. In other 356 studies, a mean crossing rate of 74.5% for the crested newt and 80.6% for the smooth 357 newt (Lissotriton vulgaris) were observed in a 'real' tunnel 24 m in length and 0.5 m in 358 diameter [START_REF] Jarvis | Road mitigation using tunnels and fences promotes site 523 connectivity and population expansion for a protected amphibian[END_REF]. About 38% of the individuals of three species of 359 Australian frogs (Limnodynastes peronii, Litoria aurea and L. latopalmata) entering a 360 tunnel 12 m long and 0.5 m wide crossed it completely [START_REF] Hamer | Usage rates of an under-road tunnel by three 21 509 Australian frog species: implications for road mitigation[END_REF]. In the 361 California tiger salamander Ambystoma californiense, 51% of individuals completely 362 crossed a 'real' tunnel 22 m in length and 0.25 m in diameter [START_REF] Bain | Evaluating the effects of abiotic and biotic factors on movement 34 465 through wildlife crossing tunnels during migration of the california tiger salamander, Ambystoma 35 466 californiense[END_REF]. In the 363 same study, the crossing rate was not influenced by the relative humidity of the 30 364 tunnel, though the mean speed of this salamander was 0.77 m/min in the dry tunnel 365 and 1 m/min in the wet tunnel [START_REF] Bain | Evaluating the effects of abiotic and biotic factors on movement 34 465 through wildlife crossing tunnels during migration of the california tiger salamander, Ambystoma 35 466 californiense[END_REF]. In the [START_REF] Hamer | Usage rates of an under-road tunnel by three 21 509 Australian frog species: implications for road mitigation[END_REF] [START_REF] Sinsch | Orientation and navigation in Amphibia[END_REF]. This may include celestial information (Diego-Rasilla and 374 Luengo, 2002), magnetism [START_REF] Diego-Rasilla | Homing ability and sensitivity to the geomagnetic field in the alpine newt, Triturus 479 alpestris[END_REF][START_REF] Diego-Rasilla | Use of a magnetic compass for nocturnal homing 487 orientation in the palmate newt, Lissotriton helveticus[END_REF][START_REF] Diego-Rasilla | Magnetic compass mediates nocturnal homing by the 490 alpine newt, Triturus alpestris[END_REF] 375 [START_REF] Fischer | Evidence for the use of magnetic map information 501 by an amphibian[END_REF][START_REF] Phillips | Two magnetoreception pathways in a migratory salamander[END_REF], and olfactory cues [START_REF] Joly | How does a newt find its pond? The role of chemical cues in migrating newts (Triturus 42 528 alpestris)[END_REF]. The 31 376 chorus attraction hypothesis [START_REF] Gerhardt | Acoustic communication in insects and anurans: common problems and diverse 17 505 solutions[END_REF] postulates that amphibians 377 can also use conspecific and heterospecific amphibian calls to locate a site of interest 378 [START_REF] Buxton | Use of chorus sounds for location of breeding habitat in 2 species 471 of anuran amphibians[END_REF][START_REF] Diego-Rasilla | Homing ability and sensitivity to the geomagnetic field in the alpine newt, Triturus 479 alpestris[END_REF]Luengo, 2007, 2004;[START_REF] James | Investigating behaviour for 520 conservation goals: Conspecific call playback can be used to alter amphibian distributions within 521 ponds[END_REF]Madden 379 and Jehle, 2017;[START_REF] Pupin | Discrimination of toad calls by smooth newts: 562 support for the heterospecific attraction hypothesis[END_REF][START_REF] Swanson | Do female frogs exploit inadvertent social information to locate 576 breeding aggregations?[END_REF]. Even non-calling species

Conclusion 412

The length of the tunnel probably influenced the proportion of complete crossings by 34 413 the fire salamander and crested newt; previous studies have recommended limiting 414 the length of wildlife passages as much as possible [START_REF] Patrick | Effective culvert placement and design to facilitate 552 passage of amphibians across roads[END_REF]. Construction 415 constraints can result in rather long tunnels, and increasing the width or diameter 416 (while keeping costs reasonable) in order to increase the use by amphibians still 417 remains to be tested [START_REF] Colino-Rabanal | Herpetofauna and roads: a review[END_REF][START_REF] Puky | Amphibian mitigation measures in Central-Europe[END_REF]. The effects of other 418 characteristics (humidity, light, substrate, etc.) also need more investigation, with 419 careful consideration of interspecific differences [START_REF] Baguette | Landscape connectivity and animal behavior: functional grain as a key 463 determinant for dispersal[END_REF]Lesbarrères 420 et al., 2010;[START_REF] Puky | Use of existing mitigation measures by amphibians, reptiles, and small 15 559 to medium-size mammals in Hungary: Crossing structures can function as multiple species-oriented 16 560 measures[END_REF].

  alter the physical environment by changing the habitat 26 55

  , landscape fragmentation caused by LTI can alter the 46 62 two main types of animal movements: (1) migration (i.e. seasonal movements 49 63 between different landscapes at different times of an individual's lifecycle), and (2) 52 64 dispersal (i.e. an individual's movement away from its birth area to reproduce in a 65 different population)

109

  distance of 800 m and are close to the town of Chantenay-Villedieu. Tunnel 3 is about 110 70 km (direct distance) from the other tunnels and is close to the town of Beaulieu111 sur-Oudon. The three tunnels consist of square concrete culvert of 1

127162

  were collected on land before reproduction (from February to early April in 2018 and 128 2019) during nocturnal transects along railway track fences. Individuals of R. 129 dalmatina were caught in water at the beginning of the species' reproductive period 130 (from February to early March 2019) with minnow traps (mesh 4 mm). P. kl. 131 esculentus/lessonae (consisting of the edible frog P. kl. esculentus and the pool frog P. 132 lessonae: hereafter, Pelophylax kl.) were caught in ponds before egg-laying (mid-May 133 2018 and 2019) manually or with a dip-net at night with the help of a flashlight. I. 134 alpestris and T. marmoratus) were caught in ponds during their reproductive period 135 (mid-May 2019) with minnow traps. T. cristatus individuals were caught in ponds 136 during their reproductive period (from mid-February to mid-May 2018 and 2019) 137 with minnow traps. A total of 1179 individuals were captured: the numbers for each 138 species are provided in Table 1. 139 The captured specimens were marked with transponders (PIT-tags, 1.4 x 8 mm, 140 weight 34.2 mg, Biolog-Tiny REF 10268 [R02-0717]), consisting of electronic chips 30 141 packaged in a 'biocompatible' glass ampoule that meet international standards for 142 animal identification (ISO 11784/11785). The animals were anaesthetized with 2% 143 xylocaine (ointment). The PIT-tags were injected subcutaneously at the intersection 144 of the belly and flank with a PIT-tag injector (Biolog-Tiny REF 10268 [R0 955]. They 145 were housed in several opaque plastic tanks (0.80 × 0.40 × 0.25 m) with moist forest 146 litter. They were kept outside, close to the capture site, in a shaded place with an 147 ambient temperature ranging from 5°C (night) to 15°C (day). The time spent in 50 captivity between capture and the experiment was about 1-2 days for newts, toads 52 148 149 and frogs. As the number of S. salamandra captured in a night could be low, some of 150 these individuals were housed for up to 10 days. The results obtained with 13 151 individuals housed 1 to 5 days and individuals housed 6-10 days were similar 152 (χ2 test, P-value=0.47). The individuals were released at the place of capture the day 153 after the experiment. Authorization to catch amphibians was provided by the 154 regional government of the study area (Regional Environment, Housing and 155 Planning Agency of Sarthe, Mayenne and Ille-et-Vilaine, interprefectoral derogation 156 from the prohibition to capture and transport specimens of protected animal species, 157 29 May 2017). The protocols used in this study were approved by the Ethical 158 Committee of UMR 5175 CEFE (Montpellier, France), decision of the committee held Before an experiment, each individual was identified by a hand-held RFID reader 30 163 (reader RS1-F1, Biolog-ID©, reading distance = 4 to 10 cm). One experimenter with a 14 164 reader was positioned at the entrance and another at the exit of the tunnel. The tested 165 individual was released at the entrance of the tunnel and the exact time recorded 166 (min). If the individual did not move in the tunnel after 10 min, it was returned to a 167 new storage tank. Individuals that entered the tunnel but then did a U-turn and 168 exited at the entrance were returned to a new storage tank after noting the exact time 169 of exit. If the individual crossed the tunnel, the experimenter at the exit noted the 50 individual's number and the exact time of exit and then returned it to a new storage 52 170 171 tank. 172 The experiments were conducted over 22 nights from March 2018 to May 2018 173 and from February to May 2019 (tunnel 1 =7 nights, tunnel 2 = 7 nights, tunnel 3 = 8 174 nights). They were performed after sunset (from about 7:00pm to 9:30pm). During a 175 test, an individual was released at the tunnel entrance every 1 min. In the case of the 176 presence of a returning individual (animals within 50 cm of the entrance and moving 177 towards the tunnel entrance), the next release was stopped until the capture of this 178 individual. The experiment was stopped 4 h 30 min after the last tested individual 179 was released at the entrance to start its crossing. The individuals that did not exit the 180 tunnel -either at the entrance or at the exit -were then collected by an experimenter, 181 identified and their position in the tunnel was recorded. of specimens in the tunnels was described by four main 185 behavioural categories: (1) 'Not moving': individuals that did not move in the tunnel 186 after 10 min, (2) 'U-turn': individuals that entered the tunnel but did a U-turn and 187 exited at the entrance, (3) 'Stay': individuals that did not exit at the entrance or at the 188 exit by the end of the experiment, and (4) 'Complete crossing': individuals that 16 189 crossed the tunnel to the exit. The proportions of each behaviour category were 50 calculated as the number of individuals displaying the behaviour divided by the 52 190 191 number of individuals tested.

  speed in tunnels of different lengths 222 In adult T. cristatus newts, the proportion of behaviour categories significantly 223 differed between tunnel 1 and 2 (tunnel 1 N = 222; tunnel 2 N = 59, χ 2 test, p-value: 224 0.00091). More 'complete crossings' and less 'U-turns' were observed in the shorter 30 225 tunnel (figure 2a). In juvenile T. cristatus newts, the proportion of behaviour 226 categories was not compared between tunnel 1 and 2 because of the low number of 227 individuals in tunnel 2 (tunnel 1 N = 16; tunnel 2 N = 3, figure 2b). In S. salamandra 19 228 adults, the proportion of behaviour categories also significantly differed between 229 tunnel 1 and 2 (tunnel 1 N = 69; tunnel 2 N = 32, Fisher-Freeman-Halton test, p-value: 230 0.00091). More 'complete crossings' and fewer 'stays' were observed in the shorter 231 tunnel (figure2c). In adult R. dalmatina frogs, the proportion of behaviour categories 50 did not differ between tunnel 1 and 2 (tunnel 1 N = 50; tunnel 2 N = 9, Fisher52 232 233 Freeman-Halton test p-value: 0.07). However, no 'complete crossings' and more 'U234 turns' were observed in the longer tunnel (figure2d). In adult B. spinosus toads, the 235 proportion of behaviour categories did not differ between tunnel 1 and 2 (tunnel 1 N 236 = 5; tunnel 2 N = 14, Fisher-Freeman-Halton test, p-value: 0.5, figure2e). This was 237 also the case for juvenile B. spinosus toads (tunnel 1 N = 7; tunnel 2 N = 15, Fisher238

243

  was also the case in T. cristatus adults (tunnel 1 N = 88; tunnel 2 N = 8, Wilcoxon-244 Mann-Whitney test, p-value: 0.31, figure3). in tunnels 1 and 2 in T. cristatus and B. spinosus adults 248 and juveniles, and in S. salamandra and R. dalmatina adults are shown in figure 2. Of 249 these species, we found that T. cristatus adults were the least likely to enter the 250 tunnels (figure 2a), while S. salamandra completed the most crossings (figure 2c), and 251 R. dalmatina did the most U-turns (figure 2c). 21 252 Concerning crossing speed, T. cristatus adults crossed tunnel 1 more quickly 253 than S. salamandra adults (T. cristatus N = 88; S. salamandra N = 47, Wilcoxon-Mann-254 Whitney test, p-value: 0.043, figure 3). 54 255 256 3.3 Acoustic enrichment in tunnels 257 In juvenile T. cristatus newts (tunnel 1), the proportion of behaviour categories 258 did not differ with or without acoustic enrichment (without N = 16; with N = 14, 259

262

  differed with and without acoustic enrichment (without enrichment N = 229; with 263 enrichment N = 46, χ 2 test p-value: 0.030). More 'complete crossings' and less 'U-264 turns' were observed in the acoustically enriched tunnel (figure 4b). However, the 22 265 crossing speed did not change (without enrichment N = 88; with enrichment N = 32, 266 Wilcoxon-Mann-Whitney test p-value: 0.63, figure 5). In tunnel 2, in adult T. cristatus 267 newts, the proportion of behaviour categories did not differ with or without acoustic 30 268 enrichment (without N = 59; with N = 46, Fisher-Freeman-Halton test, test p-value: 269 0.22, figure 4c), nor did enrichment change the crossing speed (without N = 8; with N 270 = 7, Wilcoxon-Mann-Whitney p-value: 1.0, figure 5). In tunnel 3, the proportion of 271 behaviour categories in adult T. cristatus newts did not differ with or without 272 acoustic enrichment (without N = 62; with N = 71, Fisher-Freeman-Halton test, test p-273 value: 0.57, figure 4d), nor did enrichment change the crossing speed (without N = 274 17; with N = 15, Wilcoxon-Mann-Whitney test p-value: 0.31, figure 5). 275 In adult T. marmoratus newts (tunnel 3), the proportion of behaviour categories 276 did not differ with or without acoustic enrichment (without N = 14; with N = 14, 277

284

  significantly differed with and without acoustic enrichment (without enrichment N = 285 228; with enrichment N = 35, χ 2 test, p-value: 1x10 -13 ). The four categories showed 286 marked changes in the enriched tunnel: only one individual did not move, only one 287 individual stayed in the tunnel, and only one did a U-turn. The majority, 91% (N = 288 35), of the tested frogs completely crossed the enriched tunnel (Figure 4g). Moreover, 24 289 the crossing speed in this tunnel was doubled (without N = 55; with N = 32, 290 Wilcoxon-Mann-Whitney test, p-value: 7.7 x10 -7 , Figure 5). 291 292

421FigureFigure 2 :Figure 3 :FigureFigure 4 :FigureFigure 5 :FigureFigure 1 :

 23451 Figure

  . Wildlife managers have

		107
	95 2	108
	3
	96
	26
	97
	98
	99
	100
	101
	102
	103
	104
	87	begun capitalizing on this acoustic attraction to lure animals to specific places by
	88	10 11 92
	105	12
	89	13 14
	90 106	15 93 16
		17
	91	18 94
		8

  Hyla arborea, the two main species 202 using mating calls in the ponds in our study area. The recordings were made with an 30

	215	different lengths and with or without acoustic enrichment) using the Fisher216
			Freeman-Halton test or χ 2 test (depending on the sample size for each behaviour
	203 217	omnidirectional microphone (Sennheiser ME62/K6, flat frequency response between category). The mean speed of individuals that completely crossed a tunnel was
	218	compared between tunnels with a Wilcoxon-Mann-Whitney test.
	197
	198	2.5	Acoustic enrichment
	199	In 2019, an acoustic enrichment experiment was performed during the crossing
	212
	213	2.6. Statistical analysis
	214	The proportion of each behaviour category was compared between tunnels (of
		18

192

Additionally, in two Urodela species (T. cristatus and S. salamandra), the 193 crossing speed in tunnels 1 and 2 was evaluated for individuals that entirely crossed 194 the passage. This was estimated by the length of the tunnel (in metres) divided by the 195 time taken to completely cross the tunnel (in minutes). The mean speeds between 196 tunnels were compared with a Wilcoxon-Mann-Whitney test. 200 experiments. In this test, we used a soundtrack of a mixed chorus of edible frog 201 Pelophylax kl esculentus and European tree frog 204 20 Hz and 20 kHz) coupled with a Fostex FR2LE recorder. The signal was sampled at 205 44.1 kHz with a 16-bit dynamic. Files were saved in .wav format. The stereo 206 soundtrack was emitted using a D-Jix M349BT MP3 audio player connected to two 207 loudspeakers (BOOM 2, Ultimate Ears). The loudspeakers were installed outside the 208 tunnel, 10m from the exit and space 5m apart. The average amplitude of the signal 209 emitted was set at 74.8 ± 0.8 dB with a Lutron SL-4001 sound level meter (mean ± SD, 50 1 m from the loudspeaker, C weighting, slow settings, re: 20 µ Pa ). The number of 52 210 211

individuals and the species tested in these experiments are provided in Table

1

.

  study, The length of the crossed tunnels did not affect the speed of either S.

	366	Australian frogs had a mean speed of 0.8 m/min. In our experiments, adult T.
	367	cristatus newts crossed the 21-m tunnel at a mean speed of 0.39 ± 0.03 m/min (N=88),
	368	which was faster than the S. salamandra adults (mean speed = 0.29 ± 0.02 m/min,
	370	salamandra or T. cristatus.
	371	When amphibians migrate or disperse and seek to orient themselves when
	372	moving from point A to point B, they can use a redundant, multisensory orientation
	373	system

369

N=47).

  Bufotes viridis)[START_REF] Pupin | Discrimination of toad calls by smooth newts: 562 support for the heterospecific attraction hypothesis[END_REF]. Adult T. critatus orientate to the call of the B.Jehle, 2017).. Similarly, the palmate newt Lissotriton helveticus did not orientate to R.

	400	context of wildlife passages for both Anura and Urodela species. Enrichment
	389	common frog call was explained by the fact that the newt's breeding migration did
	401	increased the proportion and speed of Pelophylax spp. crossing the tunnel (conspecific
	390 402	not overlap with the frog's calling period. These four cited studies were performed in call). In newts, broadcasting heterospecific calls resulted in T. cristatus adults
	403	completing more crossings and doing less U-turns in the 'enriched' tunnel 1 (the
	391	experimental conditions using circular arenas. Very few studies have used acoustic
	392 enrichment to direct amphibians towards a target in nature. Of these, the 30
	393	colonization of new ponds by the green and golden bell frog (Litoria aurea) was
	380	such as newts can exhibit positive phonotaxis for sympatric anuran songs: adult
	381 394	marbled newts (T. marmoratus) orientate to the calls of the E. calamita) (Diego-Rasilla encouraged using acoustic enrichment (speakers with conspecific frog calls, James et
	382	and Luengo, 2004). Adult palmate newts (Lissotriton helveticus) orientate to the calls
	408	383 of Iberian water frog Pelophylax perezi) (Diego-Rasilla and Luengo, 2007). Adult L. passages needs to be confirmed by testing more individuals and using other calls and
	384 409	vulgaris orientate to the calls of the common toad (Bufo bufo) and European green tunnel characteristics.
	385 toad (386 bufo, but not to that of the sympatric common frog (Rana temporaria) (Madden and 410
	398 411	To our knowledge, no previous studies have been conducted on acoustic
	387
	399	enrichment in natural environments with Urodela species, and particularly in the
	388	temporaria calls ((Diego-Rasilla and Luengo, 2007). This lack of response to the
		32 33

395

al., 2015). Similarly, the Cope's gray treefrog (Hyla chrysoscelis) and the American 396 toad (Anaxyrus americanus) colonized new habitats where conspecific chorus calls 397 were broadcasted

[START_REF] Buxton | Use of chorus sounds for location of breeding habitat in 2 species 471 of anuran amphibians[END_REF]

. 404 speed was unchanged). However, this difference was not observed in 'enriched' 405 tunnels 2 and 3. For the marbled and alpine newts, no effect of acoustic enrichment 406 was observed on the proportion of crossings in tunnel 3. These divergent findings 407 suggest the effect of acoustic enrichment on the behaviour of newts in wildlife

Acknowledgements

management is poorly known, further investigation would be valuable in evaluating 438 this in wildlife passages for small fauna.

Declaration of interests

☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:


Cintli Aguilar-Maldonado

Eugenia P Arévalo-López
email: angel.arevalo-lopez@univ-lille.fr

Clemens Ritter

Olivier Mentré

M Arévalo-Ló- Pez

Magnetic structures of Mn 11 Ta 4 O 21 and interpretation as an hexagonal A-site manganite

Mn11Ta4O21 is presented as the first Hexagonal A-site Manganite. Based on simple rules, the structure is compatible with a 14Hlayer (cchchch)2 stacking sequence; related to BaVO3 and BaCrO3 high pressure polymorphs. The A-site over-stoichiometry is explained through difference in ionic radii sizes between Ba and Mn. Magnetic properties show two transitions at TN1 = 88 K and TN2 = 56 K. Neutron powder diffraction evidence two magnetic structures with purely antiferromagnetic and ferrimagnetic orders below TN1 and TN2 respectively. A complementary description with 14H-(hhccccc)2 sequence of only Mn octahedra provides a direct comparison with BaMnO3-δ hexagonal perovskites and naturally explains the AFM order. Below TN2 a magneto-elastic coupling along with uniaxial negative thermal expansion are observed.

Introduction

ABO3 oxide perovskites are amongst the most studied materials due to their structural, chemical and physical properties versatility associated with a diversified field of applications. Besides the most commonly admitted cubic (c) -based 3C (e.g. SrCrO3) [START_REF] Arévalo-Lopez | Hard-soft" synthesis of SrCrO3-δ superstructure phases[END_REF] stacking sequence of AO3 layers, hexagonal perovskites show a mixture of (c) and hexagonal (h) stackings, with the end member being the 2H (h)2 (e.g. BaNiO3) polytype [START_REF] Darriet | Structural relationships between compounds based on the stacking of mixed layers related to hexagonal perovskite-type structures[END_REF]. In recent years, the incorporation of Mn 2+ into the A-site of perovskites has gained interest due to the allowance of complex electronic and magnetic A-B interactions. For example, the spintronic material Mn 2+ V 4+ O3 with localized and magnetically ordered Mn 2+ 3d 5 and itinerant V 4+ 3d 1 electrons [START_REF] Markkula | Incommensurate spin order in the metallic perovskite MnVO3[END_REF]. Several Mn2BB'O6 double perovskites and corundum related structures have also been obtained with Mn 2+ at the A-site [START_REF] Vasala | A2B′B″O6 perovskites: A review[END_REF][START_REF] Arévalo-López | Magnetic frustration in the high-pressure Mn2MnTeO6 (Mn3TeO6-II) double perovskite[END_REF][START_REF] Faik | Crystal structures and temperature-induced phase transitions of Sr2Mn 2+ W 6+ O6, and of its transformation to Sr2Mn 3+ W 6+ O6+δ[END_REF][START_REF] Tyutyunnik | Crystal structure and magnetic properties of double perovskite Mn2FeSbO6[END_REF]. However, all of these A-site manganite phases require the use of high pressure -high temperature synthesis techniques which restricts somehow the available amounts of sample. It is therefore appealing to search for more easily synthesized analogues where Mn is found on the A-site. Regarding the MnO-Ta2O5 system, different stoichiometries have been obtained via solid state routes, Mn4Ta2O9, Mn3Ta2O8, MnTa2O6 and Mn11Ta4O21 are the most notorious ones. From those, only the first two have been properly characterised, with multiferroic and optical properties respectively [START_REF] Rickert | Selective Crystal Growth and Structural, Optical, and Electronic Studies of Mn3Ta2O8[END_REF][START_REF] Grins | Determination of the magnetic structure at 10 K of Mn3Ta2O8, and refinement of the crystal structure at 295 K, using neutron powder diffraction data[END_REF][START_REF] Panja | Anisotropy in the magnetization and magnetoelectric response of single crystalline Mn4Ta2O9[END_REF][START_REF] Grins | Structure and Magnetic Susceptibility of Mn11Ta4O21 and Refinement of the Mn4Ta2O9 structure[END_REF]. Mn11Ta4O21 possesses a structure which has previously been described as consisting of alternating Mn4Ta2O6 and MnO layers and it shows a well-defined maximum at 23 K in the magnetic susceptibility [START_REF] Grins | Structure and Magnetic Susceptibility of Mn11Ta4O21 and Refinement of the Mn4Ta2O9 structure[END_REF]. In this paper, we re-examine in more detail the Mn11Ta4O21 oxide and show how it can be described as a 14H-layer hexagonal perovskite, making it the first Hexagonal A-site Manganite (HAM). It can be synthesised by conventional solid-state methods, lifting the restriction of small quantities from high-pressure A-site manganites. Magnetic susceptibility measurements and neutron diffraction show two magnetic transitions which correspond to a spin reorientation from an antiferromagnet to a ferrimagnet with a 2 µB remnant magnetisation at low temperatures. Experimental Stoichiometric amounts of MnO and Ta2O5 (Alfa Aesar) were mixed in an agate mortar, pelletized and sealed into a quartz ampoule. The pellets were heated to 900 ºC for 12 hours, ground, pelletized, sealed and heated again. A small amount of Mn4Ta2O9 was detected (<10%) and considered in the interpretation of our results. X-ray diffraction (XRD) was performed on a Cu-Kα1 Bruker D8 Advance diffractometer on a Bragg-Brentano geometry in the 5 < 2θ < 90º range. Synchrotron XRD were collected at room temperature using the BL04 beamline at ALBA, Barcelona (λ = 0.412845 Å). Neutron powder diffraction (NPD) data were taken between 1.5 and 120 K every 10 K using the D1B beamline at the ILL, Grenoble (λ = 2.52 Å). Magnetic measurements were performed on a Physical Properties Measurement System (PPMS) Dynacool (9T) system from Quantum Design. Zero field cooling (ZFC) and field cooling (FC) procedures between 2 < T < 300 K under a 0.1 T magnetic field and magnetization versus field between -9 and 9 T at various temperatures were measured. Dielectric properties were measured using an Agilent E4980A LCR meter. Electrodes were prepared on the sample with silver paste on the planar surfaces. Rietveld refinement was done with Fullprof Suite; magnetic symmetry analysis was performed using the program BasIreps implemented in the same software [START_REF] Rodriguez-Carvajal | Recent advances in magnetic structure determination by neutron powder diffraction[END_REF]. Mode analysis was made with the ISODISTORT internet-based tool [START_REF] Stokes | ISODISTORT[END_REF][START_REF] Campbell | ISODISPLACE: A Web-Based Tool for Exploring Structural Distortions[END_REF]. 1 show that within the manganese octahedra Mn3O6 (point group symmetry 3 ), Mn5O6 and Mn6O6 are the less distorted, while Mn4O6 is strongly stressed as Mn4 is off-centered by 0.79 Å from its octahedra (D parameter in Table 2). In Figure 1b the structure is drawn in a representation which highlights the similarity with the hexagonal 14H-type obtained from high-pressure synthesis observed for BaVO3 [START_REF] Chamberland | Alkaline-earth vanadium (IV) oxides having the AVO3 composition[END_REF] and BaCrO3 ( 17) with a (cchchch)2 stacking sequence, see Figure 1b andc. Only one octahedral is drawn at each layer height for Mn11Ta4O21 (Figure 1b, left): Either a TaO6 or the less distorted MnO6 when only manganese is present in the layer, i.e. Mn3O6 and Mn5O6 vs. Mn4O6 and Mn2O6. The two main differences with the 14H-sequence of BaVO3 and BaCrO3 stem from an over-stoichiometry on the A-site, resulting in Mn8(Mn3Ta4)O21, which is accounted for on the Mn6 site and marked with a red ellipse in Figure 1b (left) and its stoichiometric equivalent in Figure 1b (right). This A-site over stoichiometry is not so un-common, observed as well for instance in the parent compound Ca3Co2O6 and in the full series of hexagonal perovskite related A1+xBO3 compounds built on prismatic/octahedral columns [START_REF] El Abed | Crystal structure of a modulated composite structure with two subsystems: Ba1.1064CoO3[END_REF]. In this series the equivalent stoichiometric form would be the 2H hexagonal perovskite e.g. BaNiO3, with 1D chains as distinctive motifs. Therefore, in the present case, a more suitable formulation would be A(n+1)BnO3n with n = 7.

The second difference between the two sequences is seen when using a modular description where a mirror-reflection twinning operation (broken-black line in Figure 1b) acting on a third of the structure (red rectangle in Figure 1b) is needed to transform one structure into the other [START_REF] Ferraris | Crystallography of Modular Materials[END_REF]. This tectonic approach resembles the EMMA method for building functional inorganic materials where the stacking of blocks would dictate the functional or multifunctional (by assembly) properties of the material [START_REF] Dyer | Computationally assisted identification of functional inorganic materials[END_REF]. In here, Mn4, the central atom at the twinned block, modifies drastically the structure and the magnetic properties as described below.

In the ideal case, without Mn4 over-stoichiometry, Mn2 would be displaced towards a more A-site type coordination through a typical "push and pull" scenario" as depicted in Fig. 1d. As mentioned before, Mn1 and Mn4 are the most distorted octahedra and they are the most related to the A-site in perovskites. Figure 1e) shows the comparison with the equivalent A-site in 14H-BaCrO3 and BiFeO3, one of the most studied multiferroic perovskites. The similarity in the icosahedral coordination can clearly be seen The Mn-O bond distances to this A-site type coordination go up 3.628(8) Å as detailed in Table 2. This distance is not so far from the 3.45 Å for Bi-O bonds in BiFeO3. Moreover, the icosahedral square-face sharing between Mn1 and Mn4 is also observed in 14H-BaCrO3 and BiFeO3. However, the displacement from the oxygen from its ideal position in a compact type allows several stacking sequences as detailed later. The ZFC and FC magnetic susceptibilities of Mn11Ta4O21 were measured under a 250 Oe external field (Figure 2a-top). A sharp antiferromagnetic (AFM) magnetic transition is observed at TN1 = 88 K. The derivative (dχ/dT, inset Figure 2a) shows a second transition at TN2 = 56 K where also a ferromagnetic component is implied by the ZFC -FC divergence. Curie-Weiss fit to the inverse of susceptibility above 125 K gives µeff = 5.42 µB/Mn, close to the expected value of 5.92 µB for spin only Mn 2+ (S = 5/2). The negative Weiss constant θ = -248(1) K shows predominant AFM interactions. However, magnetisation curves under applied field at different temperatures (Figure 2a-bottom) show field induced correlations below TN1 with a probable origin from disordered spins in Mn4 as detailed later. Just below TN2 a clear ferrimagnetic contribution appears with a 2 µB per f.u. (formula unit) remnant magnetisation at 2 K. The resulting moment observed in magnetisation curves below TN2 comes from an imbalance between different Mn spin components as later described.

Rietveld refinements to NPD collected at 100 K and K are shown in Figure 2b. These confirmed the well-ordered distribution between Mn and Ta due to the large difference in neutron scattering lengths (-3.73/6.91 fm for Mn/Ta). Magnetic diffraction peaks appear below TN1 and were indexed with a k = [0 0 0] propagation vector (Γ point of the first Brillouin zone). Since the structure contains six independent Mn sites, initial magnetic symmetry analysis performed with BasIreps tool in Fullprof Suite [START_REF] Rodriguez-Carvajal | Recent advances in magnetic structure determination by neutron powder diffraction[END_REF] and the subsequent trial refinements were unsuccessful. However, a different approach with a full magnetic space group description obtained from the ISODISTORT web-based tool (13) was adopted and two subsequent magnetic structures have been discovered in Mn11Ta4O21. Below 90 K and in accordance with magnetic susceptibility measurements, magnetic intensity is observed in the NPD data. The best fit to the 60 K NPD data was obtained with the mΓ3+ irreducible representation in a {(2, 1, 0), (0, 1, 0), (0, 0, 1)} pseudo-orthorhombic supercell with the monoclinic C2'/c' magnetic space group (15.89) as shown in Figure 2e top and Supplementary Figure 1. This high temperature magnetic structure can be described as FM layers (with Mn2 and Mn5 in the same layer) coupled AFM along the c direction with idle Mn4, but ordered spins for the rest of the Mn cations along the y axis in the pseudo-orthorhombic cell (see Figure 3). Below 60 K, extra magnetic contribution grows, as shown in Figure 3d. The low temperature magnetic structure differs from the previous by the activation of a FM complementary mode in the same mΓ3+ irreducible representation and implies a spin reorientation; note that mΓ2+ is present as second order parameter (i.e. it is not sufficient to reduce the symmetry but is still present in the transition). mΓ2+ implies FM ordering along the c direction and it was tested as a possible trigger for the transition at TN2, however following a 3σ criterion (i.e. mode amplitudes < 3σ were fixed to zero) we can conclude that the only responsible for the transition is mΓ3+. Mn1, Mn2, Mn3 and Mn4 develop a mx spin component. Mn5 and Mn6 moments were constrained to be antiparallel along the whole temperature range and release of this constrain result in unstable refinements and unphysically high moments for Mn5 and Mn6. The refinement from a 1.5 K -100 K difference pattern is shown in Figure 2e bottom. Figure 3c shows the behaviour of the Mn moments and the angle φ with the x axis. The moments converge to 4.3(3), 3.1(2), 3.8(2), 2.7(3), 4.0(3) µB for Mn1, Mn2, Mn3, Mn4 and Mn5(Mn6) at 1.5 K. Obviously, the resulting moment observed in magnetisation curves below TN2 comes from an imbalance between different Mn-mx. The resultant ferrimagnetic moment at 1.5 K from NPD is mx = -0.7(1) µB, which accounts for the moment observed in the magnetic hysteresis loops after alignment in Figure 2b. Figure 2c shows the saturated moment above 5 T extrapolated to B = 0 with a clear increase below 60 K. The thermal evolution of the cell parameters in the magnetically ordered state are shown in Figure 4a. They were refined in the pseudo-orthorhombic magnetic cell and show no significant deviation from the hexagonal cell i.e. a ≈ b/√3. Below TN2 = 56 K a uniaxial negative thermal expansion develops along the c direction, implying that the FM interactions are frustrated, i.e. the lattice expands to relief this frustration maximizing the distance between the different atoms below TN2 while undergoing the ordering of the FM component [START_REF] Ablitt | The origin of uniaxial negative thermal expansion in layered perovskites[END_REF]. This can also be observed in the heat capacity measurements. Figure 4b shows the magnetic contribution to the heat capacity after subtraction of the phonon part fitted with a two terms Debye model as detailed in SI, with a negligible electronic contribution to the heat capacity. A sharp λ-type transition can be observed at TN1 = 88 K with a broad magnetic contribution below TN2 = 56 K. The calculated entropy rises up to ~140 J mol -1 K -1 at 150 K, reaching 85% of the expected theoretical value for Mn11Ta4O21 with N = 11, S = 5/2 (for Mn 2+ ) from NRln(2S+1) (164 J mol -1 K -1 ). Low temperature dielectric measurements show an increase of the capacitance under a 9 T magnetic field at TN2 (Figure 4c). A broad maximum is also observed in the dielectric loss (tan δ) above TN2. This is in agreement with group theory: using ISOSUBGROUP with the mΓ3+ irreducible representation acting over P-3c1 and an ordered parameter direction (a, a/√3) (C2'/c') one can predict a proper ferroelastic and a proper ferromagnetic material [START_REF] Stokes | ISODISTORT[END_REF].

In the previous part, a relation of the Mn11Ta4O21 structure to over-stoichiometric A-site hexagonal perovskites was established as A(n+1)BnO3n with n = 7 and a (cchchch)2 stacking sequence. The over-stoichiometry is unusual since most of the hexagonal polytypes alleviate the less-stable face-sharing octahedra motif by either metal-metal bonding (e.g. 4H-Ba-RuO3), ordered substitution of cations with small valence (e.g. Ba4Nb3LiO12) or via formation of B-site vacancies (Ba5Ta4O15) [START_REF] Mitchell | Perovskites Modern and Ancient[END_REF]. In this case, the atypical off-centering of next layer Mn in linear oligomers breaks the M-M interaction and stabilizes the structure. From a simple comparison with 14H-BaCrO3 and 14H-BaVO3, the interlayer separation (c/14) is 2.32 and 2.29 Å respectively but for Mn11Ta4O21 it results in 2.43 Å. For the octahedrally coordinated B-site cations this larger interlayer space appears comfortable when compared with an average ionic radius from 6 VI Mn 2+ and 8 VI Ta 5+ layers (0.72 Å) against the smaller VI Cr 4+ (0.55 Å) and VI V 4+ (0.58 Å). However, for the A-site cations, the large mismatch between VIII Ba 2+ (1.42 Å) vs. VIII Mn 2+ (0.96 Å) is reduced by the insertion of an extra A-site Mn layer, and therefore the 14H octahedral skeleton holds without a strong structural modification e.g. as in Ca3Co2O6-series mentioned above with A3A'BO6 general formula and A' in a trigonal prism coordination, not present in Mn11Ta4O21. However, in terms of magnetic interactions, it is more useful to compare a polyhedral sequence build on MnO6 octahedra. Figure 1c shows for instance a (hhccccc)2 sequence with only MnO6 octahedra, again selecting in layer heights having two MnO6 octahedra only the less distorted Mn3O6 and Mn5O6 but not Mn4O6 and Mn2O6. This periodic fragment has been observed in for instance 21R-Ba7Ca2Mn5O20 as (hhccccc)3 [START_REF] Floros | The n=2 Member of the New Layered Structural Family Ba5+nCa2Mn3+nO3n+14 Derived from the Hexagonal Perovskite: Ba7Ca2Mn5O20[END_REF]. To see the usefulness of this alternative description, consider the Mn11Ta4O21 magnetic structure at 60 K, shown in Figure 3b. The magnetic structure at high temperature can be thought in terms of AFM coupling between adjacent layers and with a strong frustration in Mn4 originating from the interactions with next AFM Mn1 and Mn3 layers. It can be seen that the ordered structure is mainly dictated by the B-lattice (see Table 3), i.e. Mn1 (3.2(2) µB), Mn3 (2.5(2) µB), Mn5 (3.2(2) µB) and Mn6 (3.2(2) µB), while Mn2 (1.2(2) µB) and Mn4 (0.0(2) µB) are less important. These decisive four manganese cations are the ones defining the (hhccccc) sequence and validate this alternative structural view. It is also interesting to consider the Mn1-Mn3-Mn1 face sharing octahedra trimer (see Figure 1c). Below TN1 the trimer shows solely AFM ordering i.e. ↑↓↑. This is also consistent with Goodenough-Kanamori-Andersson (GKA) rules and that strong antiferromagnetic coupling between spins is mediated by direct exchange (2.96 Å in between Mn1 -Mn3) and ~90° Mn -O -Mn links, formed by face sharing Mn1 -Mn3 -Mn1 octahedra (h layers). The AFM coupling along the c is explained via ~180° Mn -O -Mn super-exchange pathways formed along Mn1 -Mn5 -Mn6 -Mn6 -Mn5 -Mn1 connections (c layers). The AFM stacking of layers has also been observed in the whole BaMnO3-δ hexagonal perovskite series [START_REF] Adkin | BaMnO3-x revisited: A Structural and Magnetic Study[END_REF]. A spin reorientation due to A-site magnetic ordering was also observed in MnRMnSbO6 double-double perovskites with Mn present in both Aand B-sites [START_REF] Solana-Madruga | Double Double Cation Order in the High-Pressure Perovskites MnRMnSbO6[END_REF]. The strong magnetic interactions triggered below TN2 in Mn11Ta4O21 are reflected in the uniaxial negative thermal expansion along the c axis, a broad magnetic heat capacity and a magneto-dielectric coupling as shown in Figure 4. This coupling resembles the one observed in the ordered Mn2InSbO6 A-site manganite, which possesses as well a second magnetic transition that induces a spin reorientation in the ab plane, observed in its heat-capacity and in its magnetostriction. The expected electrical polarization of Mn2InSbO6 increases up to 25 % below the second magnetic transition [START_REF] Arévalo-López | Evolving spin periodicity and lock-in transition in the frustrated ordered ilmenite-type β-Mn2InSbO6[END_REF]. A further example of a compound having a similar behaviour is Mn2MnWO6 having a strong magnetostriction-polarization coupling [START_REF] Li | Magnetostriction-polarization coupling in multiferroic Mn2MnWO6[END_REF]. These examples show that A-site manganites appear as good playground to find new multiferroics. Mn11Ta4O21 is centrosymmetric however any coupling of the already active mΓ3+ irrep with mΓi-(i = 1, 2 or 3) would allow polarization in the structure and will develop magneto-electric properties. This has been demonstrated in the multiferroic cubic A-site manganite LaMn3Cr4O12 with G-type magnetic orderings on A-and B-sites, which cannot explain independently the observations but only assuming a trilinear magneto-electric coupling [START_REF] Wang | Observation of Magnetoelectric Multiferroicity in a Cubic Perovskite System: LaMn3Cr4O12[END_REF][START_REF] Senn | A group-theoretical approach to enumerating magnetoelectric and multiferroic couplings in perovskites[END_REF]. Similarly, structural Γi-(i = 1, 2 or 3) degrees of freedom would also allow the magnetoelectric properties to be realised. This non-linear magnetoelectric coupling has been observed in the centrosymmetric ilmenite Mn2FeSbO6 [START_REF] Dos Santos-García | Large Magnetoelectric Coupling Near Room Temperature in Synthetic Melanostibite Mn2FeSbO6[END_REF]. Moreover, Mn4Ta2O9, also with P-3c1 group, shows a magnetic response under a periodic square electric pulse, i.e. magneto-electric properties [START_REF] Panja | Anisotropy in the magnetization and magnetoelectric response of single crystalline Mn4Ta2O9[END_REF]. Although polarisation measurements are still needed to prove magnetoelectric properties, Mn11Ta4O21 shows a strong magneto-elastic coupling.

Conclusions

Summarizing, Mn11Ta4O21 has been reconsidered as an over-stoichiometric hexagonal perovskite becomes the first Hexagonal A-site Manganite. It shows a 14H -(cchchch)2 sequence, previously observed only in high-pressure BaCrO3 and BaVO3 oxides. It presents two magnetic transitions at TN1 = 88 K and TN2 = 56 K. The high temperature magnetic structure can be easily understood if one considers a different only magnetic 14H -(hhccccc)2 stacking sequence. This naturally explains the spin order in terms of direct-and super-exchange interactions following GKA rules and falling in line with all the BaMnO3-δ hexagonal perovskite series. At lower temperatures a spin reorientation occurs and a ferrimagnetic component develops from the remaining A-site manganese cations. A magnetic-structural coupling is observed at TN2 but magneto-electric properties are yet to be proven. Mn11Ta4O21 reveals that a new over-stoichiometric An+1BO3n family of hexagonal perovskites without trigonal prism coordination can be obtained and that the presence of A-site magnetic cations may demand a different structural representation in order to easily understand the magnetic behaviour.

"For Table of Contents Only"

Mn11Ta4O21 structure is presented as an hexagonal A-site manganite. It shows two magnetic transitions that belong to the same mГ3+ irrep with a strong magneto-elastic coupling.

Figure 1 .

 1 Figure 1. a) Rietveld fit of the Mn11Ta4O21 compound from 300 K SXRD data. Second row of Bragg tick marks corresponds to the Mn4Ta2O9 minority phase. b) Mn11Ta4O21 crystal structure compared with 14H-BaCrO3 showing A-and B-site selections. Only the TaO6 and the less-distorted MnO6 octahedra are drawn, see the text. Red ellipses show the 2Mn6 -1Ba equivalence. Red dotted square remarks the mirror-reflection twinned section of the Mn11Ta4O21 structure respects to the 14H-BaCrO3. c) Different stacking sequence, with only MnO6 octahedra, see text. d) Ideal coordination around Mn2 with argued displacements marked with red arrows. e) A-site comparison for Mn1 and Mn4 with equivalent sites in the 14H-BaCrO3 and BiFeO3.

Figure 2 .

 2 Figure 2. a) ZFC (blue) and FC (red) magnetic susceptibility of Mn11Ta4O9 (left axis). Inverse susceptibility is shown on the right axis and the derivative in the inset with the two transitions marked. b) Field dependent magnetisation curves at different temperatures. c) Saturated magnetisation obtained from linear fits from 5 T to 9 T of data from b). d) Rietveld of the nuclear and magnetic structures to the 100 K (top) and 1.5 K (bottom) NPD data of Mn11Ta4O21. e) Rietveld fit of the magnetic model to the 60 K -100 K (top) and 1.5 K -100 K (bottom) difference patterns. Asterisks show the most prominent changes in magnetic intensity from 60 K to 1.5 K. The second row of Bragg tick marks corresponds to the Mn4Ta2O9 secondary phase crystal and magnetic structures.

Figure 3 .

 3 Figure 3. Magnetic structure of Mn11Ta4O21 at 1.5 K (a) and 60 K (b). Left part shows half of the magnetic structure with different projections of the marked sections on the right. c) Thermal evolution of the Mn 2+ magnetic moments (left) and φ angle (right). d) Temperature evolution of the most prominent magnetic maxima. Extra contribution is observed below 60 K. Colour code respects the labelling of Figure 1.

Figure 4 .

 4 Figure 4. a) Temperature evolution of the pseudo-orthorhombic cell parameters in the magnetic state. b) Temperature dependence of Mn11Ta4O21 magnetic specific heat divided by temperature. Calculated entropy with the ideal value for 11 Mn 2+ as horizontal broken line. c) Thermal behaviour of the capacitance and the dielectric loss below 100 K. TN1 = 88 K and TN2 = 56 K are marked with vertical broken lines.

Table 1 . Atomic positions, isotropic and anisotropic thermal displacement parameters and BVS calculations obtained from the Rietveld fit of 300 K SXRD data. S.G. P-3c1, a = 5.37852(2) Å, c = 34.02833(13) Å. Site x y z B iso* U11 (Å 2 )* U33 (Å 2 )* BVS

 1

	Mn1 (4c)	0.00000	0.00000	0.08706(9)	--	0.002(1)	0.003(2)	1.89(2)
	Mn2 (4d)	0.66666	0.33333	0.1350(2)	--	0.014(2)	0.023(4)	1.90(2)
	Mn3 (2b)	0.00000	0.00000	0.00000	--	0.007(2)	0.012(4)	2.01(3)
	Mn4 (4d)	0.33333	0.66666	0.9766(2)	--	0.012(2)	0.073(4)	1.55(3)
	Mn5 (4d)	0.33333	0.66666	0.1558(1)	--	0.002(1)	0.003(1)	1.98(3)
	Mn6 (4d)	0.66666	0.33333	0.2264(1)	--	0.002(1)	0.002(1)	1.85(2)
	Ta1 (4d)	0.33333	0.66666	0.07013(5)	--	0.0071(5)	0.0057(8)	5.51(7)
	Ta2 (4d)	0.00000	0.00000	0.20517(3)	--	0.0074(5)	0.0076(8)	5.21(7)
	O1 (4c)	0.648(2)	0.705(3)	0.0385(2)	0.5(3)	--	--	-2.02(4)
	O2 (12g)	0.349(2)	0.388(2)	0.1062(3)	0.3(2)	--	--	-1.98(3)
	O3 (12g)	0.698(3)	0.675(1)	0.1814(3)	0.7(2)	--	--	-1.98(3)
	O4 (6f)	0.270(2)	0.270(2)	0.25000	0.9(3)	--	--	-1.98(2)
	* Uij symmetry constrains: U11 = U22, U12 = 0.5U11, U13 = U23 =0. Rp = 0.11, Rexp = 0.14, χ 2 = 1.13.

Table 2 . Selected bond and metal-metal distances and an- gles, octahedral distortions (Δd) and displacement from barycentre (D) for Mn11Ta4O21 at 300K. The subscript in the average indicates the number of bonds used.

 2

	dM-O	(Å)	dM-O	(Å)
	3x (Mn1-O1)	2.414(8)	3x (Mn2-O2)	2.11(1)
	3x (Mn1-O2)	2.092(8)	3x (Mn2-O3)	2.36(1)
	<Mn1 -O>6	2.252(4)	< Mn2 -O>6	2.236(5)
	3x (Mn1-O1)	3.628(8)	6x (Mn3-O1)	2.194(8)
	3x (Mn1-O2)	3.466(8)	< Mn3 -O>6	2.194(8)
	<Mn1 -O>12	2.899(4)	3x (Mn6-O3)	2.33(1)
	3x (Mn4-O1)	2.64(1)	3x (Mn6-O4)	2.142(7)
	3x (Mn4-O1)	2.11(2)	< Mn6 -O>6	2.236(5)
	< Mn4 -O>6	2.379(5)	3x (Ta1-O1)	1.93(1)
	3x (Mn4-O1)	3.37(2)	3x (Ta1-O2)	1.98(1)
	3x (Mn4-O1)	3.38(1)	< Ta1 -O>6	1.952(5)
	< Mn4 -O>12	2.875(5)	3x (Ta2-O3)	1.874(8)
	3x (Mn5-O2)	2.12(2)	3x (Ta2-O4)	2.106(9)
	3x (Mn5-O3)	2.29(1)	< Ta2 -O>6	1.990(4)
	< Mn5 -O>6	2.209(5)
	M-O-M	(°)	M-O-M	(°)
	Mn1-O1-Mn3	79.9(3)	Mn3-O1-Ta1	143.6(4)
	Mn1-O1-Ta1	92.6(4)	Mn4-O1-Ta1	86.7(3)
	Mn1-O2-Mn2	113.3(5)	Mn4-O1-Ta1	119.3(4)
	Mn1-O2-Ta1	101.7(5)	Mn5-O2-Ta1	85.8(2)
	Mn1-O1-Mn4	113.3(3)	Mn5-O3-Mn2 90.2(4)
	Mn2-O3-Ta2	134.9(4)	Mn5-O3-Mn6 123.4(3)
	Mn2-O2-Mn5	92.7(4)	Mn5-O2-Mn1 124.9(5)
	Mn2-O3-Mn5	92.0(5)	Mn5-O3-Ta2	123.8(6)
	Mn2-O3-Mn6	83.0(3)	Mn6-O4-Mn6 109.4(6)
	Mn2-O2-Ta1	137.5(3)	Mn6-O4-Ta2	132.1(3)
	Mn3-O1-Mn4	96.2(5)	Mn6-O3-Ta2	98.0(3)
	Mn3-O1-Mn4	82.4(2)	Ta2-O4-Ta2	92.8(2)
	M -M	(Å)	M -M	(Å)
	Mn1 -Mn3	2.962(3)	Mn4 -Ta1	3.181(6)
	Mn1 -Ta1	3.1582(7)	Mn5 -Ta1	2.914(5)
	Mn2 -Mn6	3.109(7)	Mn6 -Ta2	3.1880(9)
	Mn2 -Mn5	3.185(2)	Ta2 -Ta2	3.051(2)
	Mn3 -Mn4	3.205(1)
	Δd	D (Å)	Δd	D (Å)
	x 10 4 *		x 10 4 *
	Mn1 51.0	0.50	Mn5 14.2	0.41
	Mn2 31.4	0.30	Mn6 18.0	0.36
	Mn3 0	0	Ta1 1.6	0.08
	Mn4 126.2	0.79	Ta2 34.1	0.36
	*Octahedral distortions calculated from Δd=(1/6)*Σ(di-dav) 2 /dav.

Table 3

 3

	. mx and my refined moment components at 60 K (top) and 1.5
	K (bottom), mz = 0 for all atoms. Total moment and φ angle. ABO3 as-
	signment is based in (hhccccc)2 stacking sequence.
		ABO3 site in	mx	my	mTot	φ (°)
		(hhccccc)2	(µB)	(µB)	(µB)
	Mn1	B	0	3.2(2)	3.2(2)	90
			1.4(1)	4.0(3)	4.3(3)	48(3)
	Mn2	A	0	1.2(2)	1.2(2)	90
			-2.7(2)	-1.6(1)	-3.1(2)	31(2)
	Mn3	B	0	-2.5(2)	-2.5(2)	90
			2.7(2)	-2.6(2)	3.8(2)	-45(4)
	Mn4	A	0	0.0(2)	0.0(2)	--
			-2.7(3)	0	-2.7(3)	0
	Mn5*	B	0	-3.2(2)	-3.2(2)	90
			0	-4.0(3)	-4.0(3)	90
	Mn6*	B	0	3.2	3.2	90
			0	4.0	4.0	90
	* Constrained together to be antiparallel.

ACKNOWLEDGMENTS

We thank ALBA and the ILL for beamtime provided at BL04 and D1B respectively. AMAL thanks a Marie-Słodowska Individual Fellowship in the Horizon 2020 research and innovation programme under grant agreement 750971 ("KISS ME") and the ANR-AMANTS (19-CE08-0002-01) and LOVE-ME (16-CE08-0023) projects. CAM thanks CONACyT-Mexico for a post-doctoral fellowship (CVU:350841). Chevreul Institute (FR 2638), Region Hauts-de-France, and FEDER are acknowledged for funding the X-ray diffractometers and the PPMS magnetometer.

ASSOCIATED CONTENT

Supporting Information. NPD at 60 K and heat capacity treatment. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION

Notes

The authors declare no competing financial interest.