Behavioral Ecology

Cross-Fostering, i.e., the exchange of eggs or hatchlings, is a widely used technique, to disentangle genetic from environmental effects or to manipulate the clutch size. In most bird species, this manipulation is easily accepted by the social parents, leading to the conclusion that fostering has no detrimental effect. Using a dataset of four cohorts (N=298) of zebra finches (Taeniopygia castanotis), in which we fostered routinely a single egg into another nest of zebra finches, we explored potential short- and long-time effects of fostering. Noteworthy, these experiments were not designed to test this hypothesis. The objective of the egg fostering experiments was to test for parental recognition (Caspers et al. 2017) and mate choice decisions (Goluke 2018). Consequently, the aim of the present study is purely explorative. Our study confirmed previous findings that fostering has no short-term effects on the morphology and growth rates of the chicks, neither in males nor in females. However, we found that fostering has a sex-specific long-term effect. Females originating from fostered eggs had a significantly reduced lifespan compared to those from non-fostered eggs. Conversely, the lifespan of fostered males was similar to that of non-fostered males. All birds were housed in large groups, experiencing the same conditions after nutritional independence (day 35). Therefore, we can only speculate that fostering might result in early developmental stress, which may affect the individual fitness of females later in life, ultimately leading to shorter lifespans.

Acoustic signaling is key to individual and species recognition, playing a major role in sexual and social communication. Since reproductive isolation is often maintained through pre-mating mechanisms, song can be an early isolating trait leading to assortative mating, promoting reproductive divergence, and potentially contributing to speciation. However, whether song differences alone are sufficient to prevent interbreeding or if other traits also contribute, remains a matter of debate. Playback experiments provide a more direct way to test the role of song as a reproductive barrier. Here, we use playback experiments to test the hypothesis that song acts as a pre-mating barrier in two recently diverged populations of an island passerine, the Canary Islands Chaffinch (Fringilla canariensis palmae), which inhabit ecologically distinct laurel and pine forests within the island of La Palma. Assuming that male song has diverged in the two habitats, we tested if territorial males from a given habitat responded differently to songs from intruding males from their own habitat or from the other habitat type, using a closely related mainland species as a control. We found that probability of response was weaker to songs of the closely related species and to the different-habitat birds than to songs of the same-habitat birds, but differences for the latter were weak. The intensity of response followed the same pattern. Overall, song divergence between laurel and pine forest chaffinches does not appear strong enough to cause clear behavioural discrimination against individuals from the alternative habitat. Other factors such as morphological and ecological divergence associated with adaptation to local resources might better explain population differentiation. However, testing female responses will be essential to determine whether songs convey lineage-specific information that may elicit assortative mating.

The tail of birds contributes substantially to flight aerodynamics through lift generation, reduction of pressure drag, and pitch stabilization. Hummingbirds are powerful flyers, able to sustain hovering in still air, generate lift in both the up- and downstroke, and takeoff due to substantial developmental investment in their wings and corresponding musculature. Given the abundance of wing power, it is possible that tails are less essential to the aerodynamics of hummingbird flight than they are in other birds, freeing them for non-locomotor functions. Hummingbird tails are well known for their morphological elaboration as sexually selected ornaments, including sound generation. Our observations, and brief descriptions in the literature, led us to hypothesize that tail flaring may serve as another form of sexual signaling, used by males during male-male fighting. To test this, we used high-speed video to record agonistic encounters among seven species of hummingbird the field and found 95% of inter- and intra-sexual and specific contests included tail flaring. We measured kinematics of this flaring during male-male fighting of calliope hummingbirds (Selasphorus calliope, n = 5) indoors. Consistent with our hypothesis, captive males exhibited greater angles of tail flare when engaged in a fight (26.9 {+/-} 42.9{degrees}, mean {+/-} sd) than when performing solitary landing (-12.7 {+/-} 8.6 {degrees}) and takeoff (-11.1 {+/-} 6.6 {degrees}) maneuvers. We evaluate these results in the context of signaling during animal contests and propose future tests of whether tail flaring is an honest signal of individual quality and Resource Holding Potential (RHP). Summary StatementMale-male fighting is common in hummingbirds with competition over food and mates. During these competitions, tail flaring and waggle maneuvers are used as a signal of aggressive intent.

Body mass is a key organismal characteristic that impacts many physiological and ecological processes and often a strong determinant of fitness. Recent studies have documented temporal phenotypic changes in this trait in many populations, but identifying the mechanisms underpinning these changes can be difficult. Here, we use 47 years of data to analyse how adult and nestling body mass have changed over time in a great tit Parus major population in Wytham Woods (UK). Further, we link those changes to three environmental variables previously recognised as drivers of body mass: temperature, intra- and inter-specific competition and temporal mismatch with a key prey during breeding, winter moth Operophtera brumata caterpillars. Temporal analyses of adult body mass revealed contrasting dynamics at the between- and within-cohort levels, mirroring Simpsons Paradox. At the population level we report a marked decrease in body mass in adults between 1978 and 2024 (-0.042 Haldanes), and show that this results from phenotypic plasticity, driven by a negative between-cohort trend likely reflecting carry-over effects of the early environment. Within cohorts, however, trends were consistently positive likely reflecting an age-dependent mass increase. The change in adults was paralleled by a change in nestling body mass (-0.036 Haldanes). Nestling mass was negatively associated with estimated intensity of intraspecific competition, as well as inter-specific competition from blue tits Cyanistes caeruleus, as quantified by local population density. These effects carried over to adulthood, as shown by a negative association between adult mass and the population density experienced at early life. Temperature during development and mismatch with the caterpillar food supply, despite being associated with adult and nestling mass, did not explain the observed declines in mass, largely because these have not changed over time. Overall, our results illustrate the potential for effects mediated early in development to carry-over into long-term phenotypic change at later life history stages, and emphasise the value of considering multiple effects as drivers of phenotypic change in natural populations.

Sentinel behaviour occurs when individuals use raised positions to scan for predators while the rest of the group forages. Here, we investigated whether a colonial cooperatively breeding species that forages in large groups, the sociable weaver, Philetairus socius, displays sentinel behaviour. This behaviour has been reported in species with similar ecology, behaviour and foraging habits, (e.g. ground foraging in open habitats where aerial predators are common) and, hence, we expected that it could occur in sociable weavers. On the other hand, sentinel behaviour appears to be less common in species that live in very large groups. We used an experimental set-up consisting of an artificial feeding station and perches to assess occurrence of sentinel related behaviours: (i) perching events > 30s on an elevated position, (ii) head-movements and (iii) alarm calling. Birds were seldom observed perching while others fed, and those that did, perched for periods that were too short to be considered as sentinel behaviour (less than 5s on average). Our results suggest that this behaviour is uncommon or even absent in sociable weavers. We discuss whether other factors such as foraging in very large groups, or interspecific foraging associations might make sentinel behaviour less important in this species.

Protogynous sex change, where individuals first function as females and later as males, is a key life-history strategy among polygynous reef fishes. In haremic systems, sex change is typically socially regulated, with dominants suppressing subordinates sex change through aggression. Females within a harem form a size-based hierarchy that can remain stable in most species through the threat of eviction. We studied a different situation in the cleaner wrasse Labroides dimidiatus, where larger females have incomplete control, as they spend most of their time alone at their own cleaning territory. We tracked over 400 individuals for 12 months, recording growth, behavior, social organization, and sex change. We confirmed earlier reports that both sexes direct aggression primarily at those ranked immediately below them. However, we observed 30 cases where smaller females outgrew larger ones, revealing hierarchy instability. Of 42 sex change events, 43% occurred in presence of the male, and half of these early sex changers were not the largest female, but individuals overlooked by the male. Fast growth relative to harem-mates and harem switching increased the likelihood of sex change. Local population densities also influenced growth and sex change, with individuals in high-density demes growing faster and changing sex at larger sizes. Our findings reveal flexible sex change dynamics in a system with incomplete social dominance. Such incomplete control and observations that becoming male confers both higher reproductive success and survival highlight the need to expand game-theoretical and life-history frameworks to encompass such strategic flexibility. Lay summaryDominant cleaner wrasse cannot fully control subordinates as individuals occupy distinct core areas. Tracking 400 fish for a year, we found that smaller females could outgrow initially larger ones, and early sex change despite a larger male. Fast growth and harem switching increased the chances of becoming male. Population density also shaped these strategies. Our findings reveal flexible sex change dynamics in a system where becoming male confers both higher reproductive success and survival.

Communication allows organisms to quickly convey information vital for survival or fitness. Chemical communication and speed-accuracy trade-offs are ubiquitous in animal decision making. Most studies have used species which forage mainly above-ground species, tested in an epigean setting, but it remains unclear whether below-ground species behave similarly. Here, we use the below-ground ant Tetramorium alpestre to assess the efficacy of above- vs. below-ground mazes, the accuracy of decisions when using natural vs. artificial pheromones, the presence of a speed-accuracy trade-off, and the pheromones effect on aggression. Ants decided more quickly under below-ground than above-ground conditions, indicating they may be distracted by above-ground stimuli. Ants followed both natural and artificial trails but in direct competition preferred artificial trails, likely due to a higher pheromone concentration. Surprisingly, no speed-accuracy trade off was observed during path decision-making. Lastly, population origin but not pheromones affected if and how aggression occurred in presence of trail and home-range marking pheromones. We argue that the design of behavioural tests should match the lifestyle of the focal organism. We further speculate that speed-accuracy trade-offs likely are highly species- and context-specific and other factors besides chemicals seem important to trigger aggression, at least in this species.

Reproductive Character Displacement (RCD) often occurs when species with mating-related polymorphism come into secondary contact, leading to divergence in reproductive traits. Ischnura elegans and Ischnura graellsii have formed two independent hybrid zones in Spain where reinforcement has strengthened a mechanical barrier, and RCD has shaped mating-related structures, although reinforcement is asymmetric only in gynochrome females. This study examines the link between asymmetric reinforcement and asymmetric RCD. Using geometric morphometrics, we analyze prothorax shape and size in both female morphs and males, and male caudal appendages, to assess morphological divergence, determine whether gynochrome females show stronger divergence, and test for morphological covariation between male traits involved in the tandem position. Our results reveal consistent patterns of size and shape variation across species and zones: in I. elegans, androchromes are larger and resemble males in size, with clear shape differentiation between female morphs that diminishes in hybrid zones. In contrast, I. graellsii shows less consistent size differences between males and morphs, and weaker shape differentiation. Our results confirm RCD in prothorax shape in I. elegans females from both hybrid zones, but reveal that RCD in prothorax size is asymmetric, occurring only in gynochrome females from the NC hybrid zone. We also detected RCD in the prothorax shape of I. elegans males from the NC hybrid zone, extending previous evidence of RCD in male caudal appendages, while morphological covariation between male cerci and the prothorax was limited to size in I. elegans. Together, these findings illustrate how hybridization may generate morph-specific patterns of reproductive divergence.

BackgroundVolubility, the number of vocalizations per unit of time, is a relatively understudied aspect of animal communication, potentially crucial in highly social systems like cooperative breeders that depend on coordinated behavior. Callitrichid monkeys, including common marmosets (Callithrix jacchus), are often characterized as highly vocal, yet the variation in their calling rates due to context or individual differences remains poorly quantified. In this study, we systematically examined captive marmoset volubility across different social and informational contexts, call types, and individual characteristics. ResultsWe tested marmosets in dyads in different experimental conditions and recorded a total of 70,260 vocalizations. Overall, calling rates were not influenced by sex or status. Instead, volubility varied mainly with condition: rates increased when visually separated from the partner and individually encountering ecologically salient stimuli such as ambiguous objects or food, consistent with context-sensitive signaling and information asymmetry. Contact calls were more frequent in food-related contexts, indicating a recruiting function. Arousal calls were strongly predicted by age, with younger individuals calling more, especially when confronted with an ambiguous object. Food calls occurred almost exclusively during direct interactions with food, particularly during feeding. Dyadic analyses revealed covariation between callers and partners arousal calls, consistent with vocal contagion. In contrast, we found no contagion effects for food calls. Instead, food calls by a breeder encountering food increased contact calling in their naive dyad partners. ConclusionsOverall, marmoset volubility is flexible and call-type-specific, shows signatures of information sharing under information asymmetry, and highlights their nuanced communication strategies.

BackgroundPollen production is a costly investment in angiosperm reproduction, yet only a small fraction of grains reach conspecific stigmas. While pollen loss to floral visitors is well studied, the role of abiotic factors in shaping pollen fate has been largely overlooked. Understanding the relative contributions of biotic and abiotic pollen loss pathways is essential for interpreting floral trait evolution and pollination efficiency. ResultsWe quantified abiotic pollen loss in four animal-pollinated species with contrasting floral longevities and reproductive phase dynamics. Flowers were monitored for five hours after anthesis, with pollen loss compared between unvisited flowers and those receiving single pollinator visits. Across all species, substantial pollen loss occurred in the absence of visitation, ranging from 37-57% of grains. In several cases, losses to legitimate pollinators were indistinguishable from abiotic loss alone, whereas pollen-foraging honeybees removed significantly greater fractions. ConclusionAbiotic factors can account for a large proportion of total pollen loss, sometimes equalling or exceeding pollinator-mediated removal. These findings challenge the assumption that pollen loss is primarily driven by pollinator activity and suggest that floral traits such as closure, gradual pollen release, and pollen packaging may function as adaptations that minimize environmental loss. Incorporating abiotic pollen loss into studies of pollen presentation and pollinator effectiveness provides a more complete understanding of selective pressures shaping floral evolution.

Helping-at-the-nest is often viewed as a precursor to reproduction, but switching between breeder and helper roles has been documented in some species. Such flexibility should depend on the opportunities and benefits of helping, which could differ between sexes due to dispersal strategies and social structure. However, whether breeding-helping flexibility is widespread and sex-specific remains unknown. Here, we investigated sex-specific strategies in breeding-helping flexibility using a 10-year dataset (1955 individuals) on sociable weavers (Philetairus socius), a colonial cooperative breeder in which males are typically philopatric whereas females disperse. Both sexes helped for several years, with males helping more frequently than females and for twice as long (0-13 vs 0-10 years). Around 40% of non-dispersing birds never became breeders and 50% of individuals bred without helping first. Both sexes switched roles between- and within-seasons but males were more likely to alternate (respectively four and six times more than females and up 15 switches across seven years). Our study reveals important flexibility and sex differences in breeder-helper roles, consistent with sex-biased dispersal, spatial breeding proximity and possible indirect fitness benefits. These factors could play a role promoting the evolution of helping across life-stages, not only pre-reproduction, but also reproductive and post-reproductive individuals.

Parental care can shape post-fledging behaviour through provisioning, guidance and social information, yet its absence may alter how young birds establish space use and habitat preferences. We tested the consequences of absent parental care by comparing, hand-reared juvenile herring gulls released without parents with wild, parent-reared conspecifics, focusing on the first two months after fledging. Wild juveniles frequently revisited their natal nest during the first month, whereas hand-reared birds rarely returned to the release site; revisits declined in both groups by the second month but remained more common in wild birds. Wild juveniles used smaller ranges that subsequently expanded, while hand-reared birds began with larger ranges that later contracted, leading to convergence. Contrary to expectation, wild juveniles occurred in areas with higher human population density than hand-reared birds. Habitat use also differed between groups and changed over time. Early on, wild juveniles concentrated activity in anthropogenic and marine habitats, whereas hand-reared birds used rural green habitats more. Later, both groups shifted away from marine areas towards rural green habitats, reducing but not eliminating between-group differences. Short-term survival, did not differ between hand-reared and wild juveniles, indicating that parental care primarily reshaped early space use and habitat choice rather than immediate survival.

The ability of animals to innovate - solve novel problems - can shape their ecology and evolution. Here we investigate how individual traits and environmental complexity relate to successful solving of a novel problem. We presented foraging bumble bees (Bombus impatiens) with artificial flowers of not-previously-encountered shapes and recorded the bees latency to access nectar. We measured individual foraging traits across multiple trips with simple flowers that did not require innovation, and bees were foraging either in a simple or complex environment (cluttered flight arena). Bees in complex environments took longer to find and were less likely to land on novel flowers, indicating that environmental complexity may take up cognitive resources and make search more difficult. However, we did not find an effect of environmental treatment on the ability or time to access reward in novel flowers once bees had landed on them. In contrast, behavioral traits significantly predicted how quickly bees solved novel flowers. In particular, overall foraging tempo as well as routine formation, i.e. how much bees followed a fixed route on known flowers, predicted innovation - faster bees innovated faster, and bees with more repetitive foraging sequences were slower to solve the novel tasks. Overall, while the degree of evolutionary novelty in tasks or solutions is always hard to evaluate, our findings demonstrate that environment and individual traits may affect innovation in different ways. Individuals in simple environments may be more likely to detect, and individuals that are generally faster and have a lower tendency to develop fixed routines may be more likely to solve, novel tasks.

Seasonal rainfall shapes biological responses in tropical ecosystems, yet how tropical organisms integrate behavioral and physiological responses to cope with seasonality remains poorly understood. We assessed how four poison frog species with contrasting reproductive strategies respond to dry and wet season environmental conditions. We quantified spatial behavior, microhabitat use, hormone concentrations, and chemical defenses in two seasonal breeders (Allobates femoralis and Ameerega trivittata) and two year-round breeders (Ameerega macero and Ameerega shihuemoy). Seasonal breeders exhibited pronounced sex-specific shifts in space use, where males expanded their space use during the wet season, likely to track reproductive opportunities, while A. femoralis females increased their spatial use during the dry season, likely responding to foraging demands when prey resources are sparse. Year-round breeders maintained similar space use across seasons, likely reflecting their ability to access key resources within the same space to reproduce year-round. Microhabitat use was flexible, as seasonal breeders shifted toward humid refugia during the dry season and reproduction-associated microhabitats during the wet season, whereas year-round breeders selected microhabitats that facilitate continuous reproduction across seasons. Despite these behavioral responses, corticosterone, testosterone, and chemical defenses showed no consistent seasonal variation, suggesting that behavioral flexibility is decoupled from seasonal variation in these measured physiological responses. Our study suggests that poison frogs are able to buffer environmental fluctuations through behavioral flexibility. However, given the increasing unpredictability in rainfall timing and intensity as a result of climate change, how these coping strategies will function in the long term is uncertain.

Island populations are special for the study of evolutionary processes and can be a zone of incipient speciation. Recently, several island populations of House Wren in the Lesser Antilles (Dominica, St Lucia, St Vincent, and Grenada), formerly recognized as subspecies of the continental form, were reclassified as distinct species. However, much of the supporting data was fragmentary in its sampling of the different islands or equivocal in the patterns observed. Because song is a core element of mate recognition and choice, and can therefore be a key character in species identification, I report here the first detailed characterization and analysis of song for House Wren on all of the islands of the Lesser Antilles where they remain, including Trinidad and Tobago; and compare song patterns across the different islands as well as to several continental populations. Results show that song is broadly similar across all of the islands and to continental populations in high-level features of its structure, organization and delivery but is discriminably different among many of them in its more detailed features. The latter differences are consistent with the recent species splits, with the possible exception of Grenada. They also support retention of House Wren on Trinidad and Tobago as subspecies of the continental form. Results also point to the possibility of a central American origin for some of the islands and a south American origin for others, yielding a trait mosaic where islands that putatively share the same geographic origins, and are therefore presumably genetically closest, are not the most similar in patterns of song (or plumage). This pattern would therefore entail multiple intriguing instances of convergent evolutionary divergence among them that warrants further detailed study. Lay SummaryO_LII provide the first comprehensive analysis and comparison of song patterns of House Wrens for all of the islands of the Lesser Antilles where they remain, some of which are at risk of extirpation, or even extinction if they represent distinct species. C_LIO_LII use the patterns to interpret the recent taxonomic reclassification of many of these island populations as distinct species. C_LIO_LIIn their general structure, organization and delivery male song is similar across all of the islands and follows patterns common to contintental forms of House Wren distributed broadly across North, Central and South America. C_LIO_LISongs of the different islands are, however, discriminably different in their more detailed features and these differences are consistent with most, but possibly not all, of the recent species splits. C_LIO_LIFor the island populations recently reclassified as different species, the distinctiveness of male song is greatest in Dominica and St Vincent and to a lesser extent also St Lucia, and least distinctive in Grenada. Song in Trinidad and Tobago is not substantively different from populations in mainland South America which supports retaining these two island populations as subspecies of the closest continental forms. C_LIO_LISong patterns also point to different possible continental sources for some of the island populations: a source in Central America for Dominica and St Lucia; and a source in South America for the rest. If true, this creates multiple instances of convergent evolutionary divergence in trait patterns across the various islands which merits further study. C_LI

The ectoparasitic mite Varroa destructor is the most significant parasite of the Western honey bee (Apis mellifera) and a major driver of colony losses worldwide. Although extensive research has focused on behavioral and physiological mechanisms of host resistance, comparatively little attention has been paid to potential phenotypic responses of the parasite itself. Here we investigated body size variation in Varroa destructor associated with varroa-resistant and non-resistant honey bee colonies across four European countries. We quantified the dorsal shield area of adult female mites from multiple colonies differing in the honey bee colonies resistance status, using standardized digital image analysis. Across geographically distant non-resistant populations, mite body size was remarkably consistent, with a median dorsal shield area of 1.47 mm2. In contrast, mites originating from varroa-resistant colonies were consistently smaller, with a median dorsal shield area of 1.37 mm2, representing an approximately 6.8% reduction in body size. This pattern was reproducible across different geographical areas, honey bee genetic backgrounds and beekeeping practices. The striking stability of mite body size in non-resistant populations contrasted with the consistent reduction observed in mites associated with resistant hosts, suggesting a host associated shift in parasite phenotype. Because body size in arthropods integrates developmental conditions, nutritional availability and resource allocation, the observed pattern may reflect altered developmental environments and selective pressures imposed by resistant hosts. Our results show a consistent morphological shift in this globally important parasite associated with resistant hosts and suggest that dorsal shield size in Varroa could serve as a new selection marker for varroa-resistant honey bee colonies.

Corvids - members of the crow family - exhibit some of the most sophisticated cognitive abilities outside the primate lineage, yet the developmental origins of many of these abilities remain poorly understood. Here, we present a systematic review of the past 20 years (from 2005) of empirical research on corvid cognitive development, synthesising evidence across core/ foundational, social and physical cognitive domains. Using a structured search strategy and detailed coding framework, we identified 47 relevant studies spanning 16 corvid species. We evaluate and discuss developmental trajectories, species/ taxa-level variation and methodological robustness across studies. For within and between-taxa comparisons, we particularly focus on the best represented abilities in the coded sample: 1) object permanence and caching; 2) tool-use/ manufacture; 3) object manipulation and play; and 4) gaze following. Corvid developmental patterns show both parallels and divergences from those documented in primates and other taxa. However, the existing corvid evidence base is constrained by small samples, captive biases, limited longitudinal data and under-representation of key cognitive abilities, such as executive function, causal reasoning, self-control, metacognition, spatial memory and social learning. We outline critical gaps and future directions, emphasising the need for comparative, longitudinal and ecologically grounded approaches, including the science of magic and Theory of Mind, to better understand how early-life cognition shapes later behaviour, cognition and fitness in this model avian family.

Understanding relatedness in sharks is challenging due to uncertainty in distributions, low population densities and difficulties in sampling across life stages. In Fiji, bull sharks (Carcharhinus leucas), with an effective population size estimate of [~]258, aggregate at the Shark Reef Marine Reserve (SRMR), but gravid females disperse at the end of the year to give birth in adjacent rivers. Questions remain regarding reproductive connectivity, female returns across years, and kinship structure. Using population genomics on 296 bull sharks across age classes (neonates, young-of-the-year, juveniles, and adults) collected over a decade at the SRMR and in three adjacent rivers, we assessed familial connections. Direct genetic links, including first- and second-degree relationships, connected SRMR adults with young age classes in the Navua and Rewa rivers, providing evidence of reproductive connectivity. Within rivers, genetic similarities across cohorts revealed reproductive philopatry. Remarkably, several individuals sampled years apart were assigned to the same sire-dam pairs, indicating repeated pairings across breeding seasons. However, the few related links detected between the SRMR and the rivers may reflect incomplete sampling. Altogether, bull shark reproduction in Fiji seems influenced by reproductive philopatry and repeated pairings, suggesting added complexity in their reproductive behaviour.

Island endemic birds are under greater threat than their mainland counterparts. Sedentary living and historically reduced predation may affect island bird sociality and inform their conservation and management. However, detailed studies on their sociality are uncommon. The federally- endangered koloa maoli (Anas wyvilliana, Hawaiian duck, or koloa) is primarily threatened by hybridization with feral mallards and avian botulism outbreaks. We used capture-mark-recapture and genetic data on koloa on the island of Kaua i, a stronghold of remaining koloa, to construct social networks and examine their associations (inferred from co-occurrence in traps) and spatial genetic structure. Information on associations might shed light on preferences for or against mallards and hybrids, and inform planned translocation efforts. Microgeographic spatial genetic structuring where relatedness among individuals scales with geographic distance is a potential liability for maintaining koloa genetic diversity, and would particularly be detrimental during highly localized outbreaks of botulism that could result in the removal of entire lineages. While we found persistent social associations among adult koloa, they were not apparently influenced by plumage traits or body mass, suggesting a lack of social preference for mallard-like individuals. Importantly, we found no spatial patterns of relatedness within the largest refuge. Therefore, botulism outbreaks remain a demographic threat but are unlikely to remove correlated genetic diversity. There were no sex differences in spatial genetic structure and both sexes moved within a refuge. The lack of spatial genetic structure and the presence of many unrelated conspecifics may enable koloa to limit inbreeding and retain genetic diversity without sex-biased dispersal. In the context of future translocations, our results suggest that translocating koloa captured in the same trap together will reduce disruption of preferred associations while also retaining genetic diversity among translocated individuals. LAY SUMMARYO_LIThe koloa maoli (Hawaiian duck, or koloa) is a federally-endangered, island endemic bird. Like other Hawaiian waterbirds, koloa are threatened by introduced predators and habitat loss, but also specifically by hybridization with feral mallards and localized avian botulism outbreaks. Currently, the island of Kaua i has the largest population of non-admixed koloa. We used capture-mark-recapture and genetic data of koloa at two wetland sites on Kaua i to examine their sociality and spatial genetic structure. C_LIO_LIKoloa formed preferential social associations, but they were not based on plumage traits, body mass or genetic relatedness. C_LIO_LIThere was no spatial genetic structure for males and females within a wetland site. Our results suggested that 1) koloa have no preference for mallard-like plumage that might increase hybrid pairing, 2) localized (within-refuge) botulism outbreaks are unlikely to remove close relatives and unique genetic lineages, and 3) translocation of groups could maintain social associations without limiting genetic diversity. C_LI

Group-living animals often coordinate their behavior using "contact calls". Identifying the function of these calls requires testing whether they are intended for any group member or targeted to specific preferred associates. If contact calling is used to coordinate with preferred associates, then higher rates of contact calling are expected between group members with a history of more frequent affiliation and cooperation. To test this hypothesis, we constructed a contact-calling network using synchronized recordings of vocal interactions between all 28 possible pairs of 8 female common vampire bats with well-sampled histories of social grooming and regurgitated food sharing. Bayesian multilevel models show that pairwise rates of contact calling were clearly predicted by social grooming and cooperative allofeeding rates in ways not explained by kinship. These findings show that common vampire bats use contact calls to coordinate with specific same-sex associates, unlike other studied bat species where individuals produce contact calls at similar rates towards different group members. We also found that, compared to white-winged vampire bats, common vampire bats are ten times less likely to rapidly respond to a contact call; this suggests yet-to-be-discovered differences in social behavior between vampire bat species. Finally, we discuss implications for the vocal grooming hypothesis.