Jelena Kralj
email: jkralj@hazu.hr

Aurore Ponchon

Daniel Oro

Barbara Amadesi

Juan Arizaga

Nicola Baccetti

Thierry Boulinier

Jacopo G Cecere

Robin M Corcoran

Anna-Marie Corman

U S Fish

Leonie Enners

Abram Fleishman

Stefan Garthe

David Grémillet

José Manuel Igual

Ulrike Kubetzki

Donald E Lyons

Rachael Orben

Rosana Paredes

Simone Pirrello

Scott Shaffer

Philipp Schwemmer

Lorenzo Serra

Anouk Spelt

Giacomo Tavecchia

Davorin Tome

Cara Williamson
email: cara.williamson@bristol.ac.uk

Shane Windsor

Ruben Fijn

Active breeding seabirds prospect alternative breeding colonies

Keywords: Active breeding seabirds prospect alternative breeding colonies tracking devices, dispersal, movements, behavioural ecology, gulls, terns

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

INTRODUCTION

Prospecting behaviour is present in migratory and non-migratory, solitary and colonial species and is defined as visits of individuals to potential alternative patches where they might breed in the future [START_REF] Reed | Informed dispersal: prospecting by birds for breeding sites[END_REF]. During this process, individuals gather social and environmental information to assess the quality of potential breeding patches [START_REF] Danchin | Public information: from nosy neighbors to cultural evolution[END_REF]Dall et al 2005). Prospectors have mainly been identified in non-breeding subadults or adults, which are supposed to search for a new breeding patch [START_REF] Reed | Informed dispersal: prospecting by birds for breeding sites[END_REF]. Several empirical studies showed that prospecting occurs in many taxa such as mammals [START_REF] Selonen | Decision making in dispersing Siberian flying squirrels[END_REF][START_REF] Mares | Timing of predispersal prospecting is influenced by environmental, social and state-dependent factors in meerkats[END_REF][START_REF] Mayer | Extra-territorial movements differ between territory holders and subordinates in a large, monogamous rodent[END_REF], birds [START_REF] Reed | Informed dispersal: prospecting by birds for breeding sites[END_REF][START_REF] Doligez | Prospecting in the collared flycatcher: gathering public information for future breeding habitat selection?[END_REF][START_REF] Parejo | Blue tits use fledgling quantity and quality as public information in breeding site choice[END_REF][START_REF] Calabuig | Intercolony movements and prospecting behaviour in the colonial lesser kestrel[END_REF]Ponchon et al. 2017b), reptiles [START_REF] Cote | Social information and emigration: Lessons from immigrants[END_REF], amphibians [START_REF] Pizzatto | Finding a place to live: conspecific attraction affects habitat selection in juvenile green and golden bell frogs[END_REF], and insects [START_REF] Seeley | Nest-site selection in honey bees: how well do swarms implement the "best-of-N" decision rule?[END_REF]. During prospecting, individuals familiarize themselves with breeding patch size, local intraspecific competition, offspring quality and breeding success of conspecific or heterospecific individuals [START_REF] Mönkkönen | Evolution of heterospecific attraction: using other species as cues in habitat selection[END_REF][START_REF] Cayuela | Context-dependent dispersal, public information, and heterospecific attraction in newts[END_REF]. Individuals can use that information to make what are called 'informed dispersal' decisions about where they will breed in future years [START_REF] Clobert | Informed dispersal, heterogeneity in animal dispersal syndromes and the dynamics of spatially structured populations[END_REF]. Prospecting is especially important for immatures, as they do not have previous experience with any breeding patch apart from their natal site [START_REF] Reed | Informed dispersal: prospecting by birds for breeding sites[END_REF].

Prospecting before recruitment may affect age at first reproduction, and increase individual fitness and lifetime reproductive success (Schorring et al. 1999;[START_REF] Frederiksen | Conspecific reproductive success affects age of recruitment in a great cormorant, Phalacrocorax carbo sinensis, colony[END_REF]Genovart et al. 2020a).

Prospecting is a crucial component of informed dispersal and enables individuals to compare their current breeding patch with the neighbouring ones and make a decision on whether to stay or disperse [START_REF] Boulinier | The use of conspecific reproductive success for breeding patch selection in terrestrial migratory species[END_REF][START_REF] Reed | Informed dispersal: prospecting by birds for breeding sites[END_REF]. In general, philopatry has several advantages over dispersal, including the knowledge of the location of surrounding foraging grounds and social cohesion. The preference to breed in a familiar neighbourhood can enhance site fidelity. When emigration from a site is based on information use, dispersal is largely related to individual breeding success with failed breeders being more likely to disperse than successful breeders, especially in an unsuccessful breeding patch [START_REF] Boulinier | Public information affects breeding dispersal in a colonial bird: kittiwakes cue on neighbours[END_REF]. To decide about a future breeding patch, failed breeders prospect neighbouring patches [START_REF] Fijn | Postbreeding prospecting trips of adult Sandwich Terns Thalasseus sandvicensis[END_REF]Ponchon et al. 2017b). The degree of philopatry thus tends to be higher in stable and successful breeding patches [START_REF] Palestis | The role of behavior in tern conservation[END_REF]). Should at some point dispersal occur, many individuals can leave their current breeding patch at once, which can result in significant population size fluctuations and even collapses [START_REF] Palestis | The role of behavior in tern conservation[END_REF]Ponchon et al. 2015b;Genovart et al. 2020b). In birds, adult prospecting is mainly documented in later stages of the breeding cycle, during chick-rearing, when breeding success is easy to assess and when failed breeders have spare time before moulting or migration [START_REF] Boulinier | Spatial and temporal variations of factors affecting breeding habitat quality in colonial birds: some consequences for dispersal and habitat selection[END_REF][START_REF] Doligez | Prospecting in the collared flycatcher: gathering public information for future breeding habitat selection?[END_REF][START_REF] National Wildlife Refuge | Habitat selection by dispersing yellow-headed blackbirds: evidence of prospecting and the use of public information[END_REF]. Prospecting may also occur before the breeding season, despite time constraints associated with seasonal nesting [START_REF] Farrell | Conspecific cues and breeding habitat selection in an endangered woodland warbler[END_REF][START_REF] Spendelow | Post-Spring Migration Colony-site Prospecting by Roseate Terns (Sterna dougallii)[END_REF].

Until recently, prospecting was mainly studied from marked individuals (e.g. Ward 2005; [START_REF] Dugger | Survival differences and the effect of environmental instability on breeding dispersal in an Adelie penguin meta-population[END_REF][START_REF] Mares | Timing of predispersal prospecting is influenced by environmental, social and state-dependent factors in meerkats[END_REF]. Recent increases in the use of animal tracking technologies have begun to show how widespread prospecting behaviours can be in free-living populations. However, compared to the analysis of foraging habitat selection, breeding habitat selection is still understudied and the occurrence of prospecting in various species, including seabirds, is still not well understood [START_REF] Grémillet | Spatial ecology and conservation of seabirds facing global climate change: a review[END_REF][START_REF] Ponchon | Tracking prospecting movements involved in breeding habitat selection: insights, pitfalls and perspectives[END_REF].

Based on the collected evidence so far, prospecting in adults is commonly attributed to failed breeders [START_REF] Fijn | Postbreeding prospecting trips of adult Sandwich Terns Thalasseus sandvicensis[END_REF]Ponchon et al. 2015a;Ponchon et al. 2017b). Prospecting is energydemanding, and birds occupied with reproductive duties are not expected to spend time visiting conspecific colonies [START_REF] Reed | Informed dispersal: prospecting by birds for breeding sites[END_REF]). Yet, recently, a few tracking studies have revealed that some adults who are still actively breeding (i.e. successful in their current breeding attempt) may visit conspecific breeding patches [START_REF] Martinović | Prospecting of breeding adult Common terns in an unstable environment[END_REF][START_REF] Oro | High frequency of prospecting for informed dispersal and colonisation in a social species at large spatial scale[END_REF]. Such prospecting during active breeding is largely understudied, despite its potential broad occurrence. The fact that active breeders are devoting time and energy to prospect while also meeting the energy requirements of incubating and rearing young suggests that prospecting is an important component of habitat selection.

In this study, we collected satellite-and GPS-tracking data of 31 populations of 14 colonial gull and tern species during the breeding season to explore the occurrence of prospecting in active breeders (PAB) and assess the factors affecting that behaviour. We further analysed a subset of prospecting trips to identify their temporal and spatial patterns. Based on the numerous theoretical works which stressed that prospecting is expected to evolve especially in temporally predictable environments [START_REF] Boulinier | The use of conspecific reproductive success for breeding patch selection in terrestrial migratory species[END_REF][START_REF] Doligez | Prospecting in the collared flycatcher: gathering public information for future breeding habitat selection?[END_REF][START_REF] Bocedi | Uncertainty and the role of information acquisition in the evolution of context-dependent emigration[END_REF][START_REF] Ponchon | Prospecting and informed dispersal: Understanding and predicting their joint eco-evolutionary dynamics[END_REF], we hypothesized that PAB was more likely to occur in populations that bred in relatively stable environments. Based on the optimal timing hypothesis, according to which prospecting occurrence is the greatest during chick-rearing, when the best quality information about conspecific reproductive success can be achieved (Boulinier et al. 1996), prospecting was expected to be more frequent during chick-rearing period.

MATERIAL AND METHODS

Data collection

We collated data from studies based on satellite-and GPS-tracking of adult breeding seabirds collected through different projects that mostly aimed to study foraging movements (Table 1).

We restricted our study to gulls and terns from Europe and North America as the species of these families are known to vary in philopatry and life-history traits, and extensive tracking data during the breeding season is available [START_REF] Schreiber | Marine Birds[END_REF][START_REF] Brooke | Far from land. The mysterious lives of seabirds[END_REF]. We selected studies in areas where the position of conspecific breeding patches where known based on field research or surveying or monitoring programs. Colonies can be defined as aggregates of only-breeding territories [START_REF] Danchin | Conspecific reproductive success and breeding habitat selection: implications for the study of coloniality[END_REF]). Colony determination is often subjective and differs for each species [START_REF] Jovani | Hidden patterns of colony size variation in seabirds: a logarithmic point of view[END_REF]. In this paper, we define a "breeding patch" as a formation of clustered nests spatially separated by topographic features (single cliffs, islands, roofs, etc.).

We defined PAB (prospecting in active breeders) as the visit to other conspecific breeding patches by a breeding individual during the incubation or chick-rearing stage. Due to the different temporal resolutions of GPS/satellite positions (between 5 and 30 minutes) in the different studies, prospecting was confirmed if two successive locations (with a null speed when available) were recorded at the visited patch, indicating at least a short resting period. In populations with frequent perturbations, where breeding patches might be abandoned for several years and then recolonised, visits to all known breeding patches were categorised as prospecting, even if the patch was not confirmed to be active in the respective year [START_REF] Oro | High frequency of prospecting for informed dispersal and colonisation in a social species at large spatial scale[END_REF].

We collected data from 1196 adult individuals belonging to 14 species. In general, birds were captured towards the end of the incubation stage to reduce the likeliness of clutch abandonment and maximize the capturability. The majority (90.8%) of birds were tracked during a single breeding season (from a few days to a few weeks), while 9.2% of birds were tracked during 2 or more (maximum 5) successive breeding seasons, resulting in a total sample of 1392 birds/seasons. The sex of birds was known in 1170 cases, with 587 females and 583 males.

Gulls and terns have semi-precocial chicks that leave the nest within 2-4 days (terns) or up to 8 days (gulls) after hatching. The ledge-nesting kittiwakes are the exception with chicks staying in the nest for around 30 days [START_REF] Lance | Diet and Postnatal Growth in Red-Legged and Black-Legged Kittiwakes: An Interspecies Comparison[END_REF][START_REF] Coulson | The kittiwake[END_REF]. We used monitored or presumed nest fate to assess whether tagged birds were actively breeding. Nest fate covered the period of incubation and early chick-rearing and was monitored using cameras or through visual monitoring of nests. Alternatively, it was presumed from the movements of tracked birds, where regular visits to their breeding patch (based on GPS positions) during the incubation and early chick-rearing period were considered as indication of active breeding (e.g. Ponchon et al. 2017a;[START_REF] Picardi | Analysis of movement recursions to detect reproductive events and estimate their fate in central place foragers[END_REF]. Incubating birds or birds with young chicks were considered to be active breeders, no matter the final fate of their offspring. Movements after presumed breeding failure were not analysed. Tracked birds that failed early during tracking were not included in the analysis.

Selection of variables

We tested how intrinsic and environmental factors affected the occurrence of PAB. We recorded variables related to the birds and variables describing their breeding patch. For each bird, its identification number, species, sex, species-specific duration of incubation and chickrearing, and relative tracking duration for each breeding season were recorded. The categorical variables related to the breeding patch included in our model were patch identification number, occurrence of large breeding failure, frequent changes of breeding locations (CBL), habitat type and patch stability, whereas the continuous variables were distance to the closest conspecific breeding patch (DCC) and latitude. Additionally, for prospecting individuals, distances to the prospected patches were recorded.

Duration of incubation and chick-rearing stage until fledging is given as an average time in days, extracted from [START_REF] Bwpi | BWPi 2.0.1. Birds of the Western Paleartic Interactive DVD ROM[END_REF] and Billerman et al. (2020) for European and North American species respectively. The relative tracking duration was provided in four categories, representing < 25%, 25-50%, 51-75% and > 75% of the breeding season duration (egg-laying to fledging). We assessed whether regular breeding failure (as the result of predation, adverse weather, flooding, or food shortage) occurred at the studied patches. Information whether groups of birds frequently changed their breeding locations was often based on long-term monitoring or data obtained by colour-ringing. The type of habitat where species evolved distinguished ephemeral habitats (such as dynamic marshes, saltpans and dunes) and stable habitats (rocky cliffs, rocky islands). For defining breeding patch stability, codes were used as follows: 1 -(one of) the biggest colonies in the study area; 2 -stable but smaller breeding patch, frequently used; 3 -new or infrequently used breeding patch (Supplementary Material Table 1).

Statistical analyses

We built generalized linear mixed-effects models (GLMM) to assess the factors affecting the occurrence of PAB for each tracked individual as a binomial response variable, using categorical and continuous predictors with logit link. Relative tracking duration and breeding patch ID were included as random variables. We checked variables for collinearity and excluded the variable "species" from the models. Interactions among variables (CBL, DCC, stability, sex) were tested, but did not significantly influence the models. Model fit accounting for model complexity was evaluated using the Akaike information criterion corrected for small sample sizes (AICc, [START_REF] Burnham | Model Selection and Multimodel Inference: A Practical Information-Theoretic Approach[END_REF]. Since the top three models (lowest AICc) had ΔAICc less than two, these models were conditionally averaged using the model.avg function (Bartón 2020). Statistical analyses were conducted in R version 4.1.1 (R Core Team 2021) using the lme4 [START_REF] Bates | Fitting Linear Mixed-Effects Models Using lme4[END_REF] and MuMIn (Bartón 2020) packages.

We further aimed at identifying temporal and spatial patterns of PAB based on 322 prospecting tracks from 113 individuals from 11 species. We used Yates corrected Chi-square test to analyse the difference in the occurrence of prospecting trips between sexes, breeding stages (incubation or chick-rearing) and time of the day (day vs. night). The correlation between the distance to the closest breeding patch and prospected patches were analysed by Pearson correlation.

RESULTS

Factors affecting the occurrence of PAB

From 31 populations of 14 gull and tern species analysed, prospecting in active breeders (PAB) was recorded in 19 populations of 12 species (Table 1): 2 out of 5 tern populations and 17 out of 27 gull populations. The percentage of prospecting individuals among all breeders ranged from 0.6 to 70%. Higher percentages (>25% prospecting individuals in studies with a minimum of 10 tagged birds) were recorded among five species: Mediterranean gull, Larus melanocephalus, Audouin's gull Larus audouinii, yellow-legged gull Larus michahellis, sandwich tern Thalasseus sandvicensis and common tern Sterna hirundo.

The inter-annual change of breeding location and sex were shown to be the most important variables affecting the occurrence of PAB (Table 2). Conditionally averaged best three models (Figure 1) showed that probability for PAB was higher in populations showing frequent interannual change of breeding location (GLMM z value =3.819, p < 0.001) and among females (GLMM z value = 2.201, p < 0.01).

Analysis of prospecting trips

From prospecting trips of birds with known sex (N = 185), 61.6% were undertaken by females (Figure 2). Females had higher median prospecting distances in six species and higher maximum distances to prospected colonies in six species, but due to the small sample size, the difference was significant only for one population of Audouin's gulls (Supplementary Material Table 2). From all prospecting trips with a known stage of the breeding cycle (N= 243), 63%

were undertaken during the chick-rearing stage, with similar values (53.3-60.8%) obtained for individuals with longer relative tracking durations (>50% of the breeding season). Also, 40.8% of prospecting trips with a reported time of day (N=277) included nocturnal visits in prospected colonies. Nocturnal trips were more common during the incubation stage (51.1% of trips during that stage) than during the chick-rearing (29.4% of trips) (Yates corrected χ 2 = 4.46, p < 0.05).

The majority of visited patches were < 100 km from the breeding patch (Figure 3, Figure 4) and distances to prospected patches (range 0.8-345 km) were highly correlated to the distances to the closest breeding patch (range 0.8-385 km) (Pearson correlation = 0.368, p<0.01).

The greatest number of prospecting tracks were collected for the sandwich tern from the Netherlands (41 individuals with a total of 133 prospecting trips). For that species, the median number of prospecting trips per bird was 2 (range 1-8), while the median distance was 8 km (range: 5-202). Most prospecting trips of the sandwich tern were undertaken only during the daytime, but 39.1% of them also included nocturnal visits in prospected colonies. Also, 42.1% of trips were undertaken during the incubation stage. The percentage of trips that included nocturnal visits at the prospected colony was higher during the incubation stage (60.7%) than during chick-rearing (23.4%), the difference being significant (Yates corrected χ 2 = 7.20, p < 0.01). More nocturnal visits during the incubation stage were also found in common tern ( 5during incubation versus 1 during the chick-rearing stage), but the total number of trips was low (N =12). A substantial percentage of nocturnal visits were undertaken by Audouin's and yellow-legged gulls (47.6% and 46.2% respectively), whereas Mediterranean gulls prospected only during daytime.

DISCUSSION

Contrary to our predictions, prospecting in active breeders (PAB), a behaviour largely unnoticed in the scientific literature, was recorded in 85.7% of studied gull and tern species and 61.3% of sampled populations. During the breeding period, central place foragers like seabirds are constrained in time and energy, as they must divide their time between foraging for themselves and investing in reproduction [START_REF] Orians | On the theory of central place foraging[END_REF]. The fact that prospecting frequently occurs during incubation and chick-rearing stresses its importance in the breeding habitat selection process and might be much more widespread than currently acknowledged.

Drivers of prospecting: breeding patch, sex and distance

The relation between prospecting and inter-annual change of breeding locations is consistent with the well-supported hypothesis that prospecting helps individuals select their future breeding site [START_REF] Reed | Informed dispersal: prospecting by birds for breeding sites[END_REF]. Changing a breeding location might be preceded by sabbatical year(s), during which individuals prospect potential breeding sites [START_REF] Munilla | Colony Foundation in an Oceanic Seabird[END_REF][START_REF] Oro | High frequency of prospecting for informed dispersal and colonisation in a social species at large spatial scale[END_REF]; however, our results show that currently breeding birds also engage in PAB.

Prospecting during different stages of the breeding cycle also allows breeding individuals to compare the quality of their current breeding patch to other localities over a wider area, informing the decision of whether to disperse or not. This information could be used for the current or future breeding seasons. As <10% of individual birds in our study were tracked over multiple consecutive breeding seasons, we could not examine whether prospecting birds actually used gathered information to disperse to a prospected patch the following season.

However, [START_REF] Oro | High frequency of prospecting for informed dispersal and colonisation in a social species at large spatial scale[END_REF] found no prospecting in successfully breeding Audouin's gulls that were philopatric in the following year, and intensive prospecting in both successful and unsuccessful breeders that dispersed in the following year, highlighting the crucial role of prospecting in dispersal decision. Prospecting patterns might thus potentially reflect individuals' intentions to disperse. However, this tight link between prospecting and subsequent dispersal is still challenging to record in the field, as individuals must be tracked over long periods and large spatial scales.

We considered relative breeding patch size and frequency of its use as a proxy for the stability of the patch but also as an indicator of environmental quality. However, patch stability in our study did not have a significant effect on PAB. This contradicts previous theoretical models that showed that prospecting may only evolve in a relatively predictable and stable environment [START_REF] Boulinier | The use of conspecific reproductive success for breeding patch selection in terrestrial migratory species[END_REF][START_REF] Doligez | When to use public information for breeding habitat selection? The role of environmental predictability and density dependance[END_REF][START_REF] Bocedi | Uncertainty and the role of information acquisition in the evolution of context-dependent emigration[END_REF]). Nevertheless, those models mostly addressed prospecting where dispersal occurred the following year, not during the same breeding season. The difference in timing of information use might be crucial in an unstable environment, since in this case, information gathered during prospecting might be used immediately, such as for renesting purposes. As replacement clutches are more likely to be laid after failure in earlier stages of the breeding season [START_REF] Pakanen | Informed renesting decisions: the effect of nest predation risk[END_REF], prospecting during the incubation suggests that PAB may also be used to identify suitable patches for renesting elsewhere within the same season [START_REF] National Wildlife Refuge | Habitat selection by dispersing yellow-headed blackbirds: evidence of prospecting and the use of public information[END_REF][START_REF] Martinović | Prospecting of breeding adult Common terns in an unstable environment[END_REF]. At the same time, PAB was more common during the early chick-rearing stage than during incubation, which is consistent with the "optimal-timing hypothesis" (Boulinier et al. 1996).

Prospecting was more common in breeding females than in males, as already observed in adult breeding yellow-headed blackbirds Xanthocephalus xanthocephalus [START_REF] National Wildlife Refuge | Habitat selection by dispersing yellow-headed blackbirds: evidence of prospecting and the use of public information[END_REF]. In general, females have higher dispersal probabilities in most bird species [START_REF] Greenwood | Mating systems, philopatry and dispersal in birds and mammals[END_REF], which may explain higher prospecting rates. Similarly, in six species females travelled greater maximum distances to prospected colonies than males. It has been shown that in several seabird species, the smaller sex undertakes longer foraging trips during the breeding season [START_REF] Phillips | Causes and consequences of individual variability and specialization in foraging and migration strategies of seabirds[END_REF]). In the current study, females were the smaller and lighter sex in all seabirds examined. Therefore, they may use less energy for flying, which might be the underlying reason for their longer prospecting flights [START_REF] Wearmouth | Sexual segregation in marine fish, reptiles, birds and mammals: behaviour patterns, mechanisms and conservation implications[END_REF]. In general, parental care in studied gulls and terns is shared between sexes [START_REF] Leclaire | Family size and sexspecific parental effort in black-legged kittiwakes[END_REF][START_REF] Kavelaars | Simultaneous GPS-tracking of parents reveals a similar parental investment within pairs, but no immediate co-adjustment on a trip-to-trip basis[END_REF] with some differences among species. For example, females often perform more incubation and chickrearing, whereas males perform most territory attendance in gulls and more provisioning in terns and some gulls [START_REF] Pierotti | Male and female parental roles in the Western Gull under different environmental conditions[END_REF][START_REF] Fasola | Sex-biased parental-care allocation in three tern species (Laridae, Aves)[END_REF].

Distances to the prospected colonies were highly correlated with distances to the closest breeding patch. In our study, birds usually visited patches close to their current breeding patch, but on five occasions, visits to the nearest breeding patch (ranging 10-24 km) were not recorded. Whether active breeders visit all available patches or only some of them might depend on the number and distances to potential breeding patches, but also on the previous experience of individuals. As breeding seabirds must return frequently to their breeding patch to undertake reproductive duties, maximal prospecting distances of active breeders were expected to be lower than in failed breeders. This was confirmed in Audouin's gulls where the maximum distance to prospected patches was 164 km in active and 360 km in failed breeders [START_REF] Oro | High frequency of prospecting for informed dispersal and colonisation in a social species at large spatial scale[END_REF], and in sandwich terns, where maximal distances in active breeders (202 km) were lower than in failed breeders from the same colonies (850 km; [START_REF] Fijn | Postbreeding prospecting trips of adult Sandwich Terns Thalasseus sandvicensis[END_REF].

Nocturnal visits were recorded in 40.8% of prospecting trips and were more frequent during incubation. Frequent prospecting or longer visits to prospected colonies decrease nest attendance, creating a trade-off between nest attendance and prospecting. Peak numbers of Audouin's gulls prospecting at night were also reported by [START_REF] Oro | High frequency of prospecting for informed dispersal and colonisation in a social species at large spatial scale[END_REF]. Nocturnal visits might decrease negative interactions with conspecifics and predators while enabling the assessment of population density and breeding success.

Intra-and inter-specific differences in PAB

Kittiwakes were the exception among studied seabirds, as almost no PAB was recorded.

Previous tracking studies on breeding black-legged kittiwakes showed that prospecting only occurred in failed breeders (Ponchon et al. 2015b;Ponchon et al. 2017b). In our study, only one bird from 324 black-legged kittiwakes and two from 94 red-legged kittiwakes Rissa brevirostris prospected while actively breeding. Furthermore, the occurrence of PAB differed between populations of the same species: PAB occurred in Oregon, but was not observed in Californian populations of the western gull Larus occidentalis, whereas in yellow-legged gull, PAB was common in the Balearic population, but not in the Atlantic one [START_REF] Delgado | High philopatry rates of Yellow-legged Gulls in the southeastern part of the Bay of Biscay[END_REF], Table 1). Overall, inter-and intra-species variability calls for more detailed studies of PAB in different populations of the same species but also in species with different life-history strategies. Possible factors that could affect prospecting are differences in physical environments (e.g. populations at the core/edge of species range, number of conspecific colonies), density-dependence at both inter-and intra-specific level, a regime of perturbation, age-distribution, laying synchrony and habitat suitability (including foraging opportunities and predator density; [START_REF] Oro | Differences in diet, population increase and breeding performance between two colonies of Audouin's Gulls Larus audouinii during breeding seasons affected by a trawling moratorium[END_REF][START_REF] Tavecchia | Living close, doing differently: small-scale asynchrony in demographic parameters in two species of seabirds[END_REF][START_REF] Sanz-Aguilar | Contrasting age-specific recruitment and survival in three colonies of storm petrels: which combination is best?[END_REF].

Other factors that might influence prospecting are animal personality shown to affect dispersal [START_REF] Cote | Personality-dependent dispersal: Characterization, ontogeny and consequences for spatially structured populations[END_REF][START_REF] Schuett | Prospecting at conspecific nests and exploration in a novel environment are associated with reproductive success in the jackdaw[END_REF]) and individual experience or age [START_REF] Oro | Food availability and nest predation influence life history traits in Audouin's gull, Larus audouinii[END_REF][START_REF] Payo-Payo | Colonisation in social species: the importance of breeding experience for dispersal in overcoming information barriers[END_REF]. Older immatures individuals generally prospect less, with increased fidelity to a selected site before attempting breeding for the first time [START_REF] Cadiou | Prospecting in the kittiwake, Rissa tridactyla: different behavioural patterns and the role of squatting in recruitment[END_REF][START_REF] Dittmann | Dispersal decisions: common Terns, Sterna hirundo, choose between colonies during prospecting[END_REF][START_REF] Campioni | Albatrosses prospect before choosing a home: intrinsic and extrinsic sources of variability in visit rates[END_REF]. In contrast, older adults may be more likely to prospect, such as in meerkats Suricata suricatta [START_REF] Mares | Timing of predispersal prospecting is influenced by environmental, social and state-dependent factors in meerkats[END_REF]. Knowing the age of tracked individuals may provide greater clarity on whether individuals of different age and experience display different prospecting patterns.

The effect of data quality

In the present study, we assumed that any visit to a conspecific colony was for prospecting.

Even if we cannot rule out the possibility that some individuals visited breeding patches for other purposes than prospecting for a future breeding site (see Ponchon et al 2015a), being present in another breeding patch with other conspecifics may still provide information that could be used for dispersal and settlement decisions. Accordingly, we believe our assumption did not significantly affect our results. On the contrary, PAB evidence might still be underestimated, especially in studies involving a small number of tracked individuals or short tracking periods, or if not all conspecific breeding patches were identified and visits to these sites were not recorded as prospecting. Moreover, in our study, adults were mostly tracked from the mid-incubation stage onwards, so visits to other colonies at the beginning of the incubation stage were not recorded. Similarly, visits towards the end of the rearing stage were not included, as it was not possible to identify if breeding was over for individuals (by fledging or chick loss).

A few studies showed long-distance movements and prospecting in birds [START_REF] Boulinier | Migration, Prospecting, Dispersal? What Host Movement Matters for Infectious Agent Circulation?[END_REF][START_REF] Cooper | Hidden long-distance movements by a migratory bird[END_REF], highlighting the underestimation of the frequency and spatial scale at which animals move outside of their territories. Understanding the purpose and scale of prospecting movements and being able to relate them to actual dispersal would have important implications for the ecology, evolution, and conservation of species, especially in the current context of environmental change [START_REF] Dugger | Survival differences and the effect of environmental instability on breeding dispersal in an Adelie penguin meta-population[END_REF]Ponchon et al. 2015b). The number of tracking studies is increasing, especially in the marine environment. Although many of them aimed to identify foraging behaviour or migration routes, they might also be a source of other information [START_REF] Hays | Key questions in marine megafauna movement ecology[END_REF]. Regardless of the goal of tracking studies, more attention should be given to the movements of individuals that differ from usual foraging patterns. In species that often disperse, tracking prospecting in breeding adults as well as tracking their visits to potential, but empty patches might provide insights into their intentions in terms of current and future breeding habitat selection and colonisation of new breeding patches [START_REF] Oro | Perturbation, social feedbacks, and population dynamics in social animals[END_REF][START_REF] Oro | High frequency of prospecting for informed dispersal and colonisation in a social species at large spatial scale[END_REF]. It would also help to identify already existing breeding patches and be an important tool for planning the monitoring of breeding populations, assessing population borders and designing conservation measures.

CONCLUSION

By reviewing the occurrence of PAB among different gull and tern species, we highlighted the importance of prospecting in adult breeding seabirds. We showed that PAB is more common in populations with frequent breeding dispersal and among females. Informed dispersal may help populations to recover faster in response to environmental change by tracking better environmental conditions, notably through extinction-recolonization dynamics (Ponchon et al. 2015b). Still, little is known about the drivers that influence prospecting and subsequent settlement in a new breeding patch, including the effect of various environmental factors [START_REF] Payo-Payo | Colonisation in social species: the importance of breeding experience for dispersal in overcoming information barriers[END_REF][START_REF] Oro | High frequency of prospecting for informed dispersal and colonisation in a social species at large spatial scale[END_REF]. Our results call for more long-term tracking studies simultaneously monitoring the breeding success not only of individuals but also of whole breeding patches to identify factors affecting spatial and temporal patterns of prospecting in different stages of populations and different environments This would ultimately allow us to better predict species response to environmental change.

  Variables: CBLfrequent change of breeding location, stabilitybreeding patch stability, DCCdistance to the closest colony, habitathabitat where species evolved, RBFregular breeding failure, IFduration of incubation and fledging (for details, see Material and Methods); np -number of estimable parameters, Dev -relative deviance, AICc -Akaike's information criterion corrected for small sample sizes, ΔAICc -difference between the current model and the model with the lowest AICc, Wi -Akaike model weight.

Figure 1 .

 1 Figure captions:

Figure 2 .

 2 Figure 2. Number of prospecting trips (all studied species pooled) per sex and breeding stage.

Figure 3 .

 3 Figure 3. Distances to the prospected breeding patches by actively breeding birds. Data present

Figure 4 .

 4 Figure 4. Examples of prospecting trips of four individuals: a) western gull Larus

Table 1 .

 1 Tracking studies of seabird movements included in the analysis of prospecting in active breeders. The number of prospecting individuals refers to birds prospecting during the active breeding.References based on tracking data included in this study are provided. References related to study of prospecting movements are given in bold.

	Species	Country	Year	No. of	No. of	Percentage of	Data owners
				tracked	prospecting	prospecting
				individuals	individuals	individuals
	Rissa tridactyla France	2014	36	0	0	Ponchon, A., Grémillet, D
	Rissa tridactyla Norway	2010-	136	0	0	Ponchon, A., Boulinier, T
			2015
	Rissa tridactyla USA	2008-	152	1	0.7	Paredes, R., Harding, A.,
			2010				Orben, R.,
	Rissa	USA	2010	23	0	0	Paredes, R., Irons, D.,
	brevirostris						Roby, D.
	Rissa	USA	2015-	71	2	2.8	Orben, R., Fleishman, A.,
	brevirostris		2017				Kitaysky, A. Shaffer, S.,
							Paredes, R.
	Larus	Italy	2016	10	7	70	Serra, L., Pirrello, S.,
	melanocephalus						Cecere, J.G.
	Larus audouinii Croatia	2017-	28	12	42.9	Jurinović, L.
			2021
	Larus audouinii France	2014-	8	0	0	Recorbet, B.
			2016
	Larus audouinii Italy	2013-	30	3	10	Baccetti, N., Zenatello,
			2020				M., Amadesi, B.

Table 2 .

 2 Generalized linear mixed-effects models testing factors affecting the occurrence of prospecting in active breeding gulls and terns with relative tracking duration and breeding patch ID as random variables. The bottom model is the full model. The first three models were conditionally averaged.

	Variables in the model	np	Dev	AICc	ΔAICc	Wi
	CBL + sex	5	407.6 417.68	0	0.443
	CBL + sex + stability	7	404.7 418.78	1.10	0.256
	CBL + sex + DCC	6	407.2 419.31	1.63	0.197
	habitat + sex	5	411.2 421.23	3.55	0.075
	CBL + sex + stability + DCC + RBF
		12	398.9 423.14	5.46	0.029
	+ lattitude + habitat + IF

Acknowledgements: All authors would like to thank all colleagues and site staff / managers that helped during field work and data analyses. We appreciate the comments from anonymous reviewers who helped us to improve the paper.

Declarations

Funding: The study on black-legged kittiwakes in Norway was funded by the French Polar Institute (IPEV, programme no. 333 PARASITOARCTIQUE and OSU-OREME) and in France by Eoliennes Offshores du Calvados, Eoliennes Offshores des Hautes Falaises and the French Agency for Marine Protected Areas. Tracking of black-legged and red-legged kittiwakes in Alaska was supported by the North Pacific Research Board. The studies on Mediterranean gulls and gull-billed terns in Italy were funded by agreements between ISPRA and the Italian Ministry for the Ecological Transition (MiTE), formerly Ministry for Environment, Land and Sea Protection (MATTM); Decreti Min. Prot. 0004799 -04/03/2016 and Prot. 34751 -30/12/2019. The study of Audouin's gull in Spain was funded by the Spanish Ministry of Science, AEI/FEDER and UE (grants re. CGL2016-80963-R and CGL2017-85210-P), Project LIFE + INDEMARES (2009-2014; LIFE07NAT/E/000732), and was conducted by SEO/BirdLife. The study of Audouin's gull in Corse was founded by French Ministry of the Environment and CEN de Corse and in Italy by the Arcipelago Toscano National Park ('The BIG FIVE' project), under the LIFE project 'Resto con Life' (LIFE13 NAT/IT/0000471) and by ISPRA. Tagging of Audouin's and yellow-legged gulls in Croatia was funded under LIFE Artina project (LIFE17 NAT/HR/000594). Tracking of western gulls in Oregon was funded by the Bureau of Ocean Energy Management M14AC00026 and in

Availability of data and material:

The datasets analysed during the current study are available from the corresponding author upon reasonable request.

Code availability: NA

California by several sources including SJSU RSCA and CSU COAST. Funds to monitor yellow-legged gull movements in the Balearic Islands were provided by Agencia Estatal de Investigación (AEI) and the EU found for regional development (FEDER), project n.

Conflict of interest:

The authors declare that they have no conflict of interest.

Ethical approval: All applicable institutional and/or national guidelines for the care and use of animals were followed.

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