Behavioral Ecology and Sociobiology

Combining interaction rates of different social behaviours into social relationship indices to represent the structure of dyadic relationships on one underlying dimension is common practice in animal sociality studies. However, the properties of these relationship indices are not well explored - mainly because, for real-world social systems, the true value of relationships is unobservable. Here, we use simulation studies to estimate the accuracy and precision of three relationship indices: the Dyadic Composite Sociality Index, the Composite Relationship Index, and the Dynamic Dyadic Sociality Index. We simulated one year of social interactions for multiple groups of 25 individuals and 4 interaction types with different properties, and tested the impact of different focal follow regimes, data densities and sampling conditions on the representation of social relationships. Accuracy and precision of social relationship indices were strongly driven by sample size, similar to simple interaction rates. Under the assumption that there was a clear, one-dimensional relationship underlying interactions, and that different interaction types constituting an index were highly correlated, indices indeed increased accuracy over single interaction rates for small sample sizes. Including uninformative constituting behaviours (i.e., those not highly correlated with the underlying relationship dimension) reduced the accuracy of all indices. The precision of each index (i.e., whether multiple simulated focal follow regimes achieve the same dyadic values for the same data) was generally poor and was driven by the precision of the least precise constituting behaviour, making them less precise than some single interaction rates. Our results showed that social relationship indices do not remove the need to have sufficient data for each individual constituting interaction type. Index quality was defined by the least accurate and precise constituting interaction type. Indices might only be useful if all constituting interaction rates are highly correlated and if there are clear indications that one dimension is sufficient to represent social relationships in a group.

A major challenge in managing captive-bred rhesus macaque social groups is mitigating deleterious aggression before it escalates to social instability. Prior work at the California National Primate Research Center (CNPRC) showed that fragmentation of matrilineal structure--reflected in lower average kinship among female kin--is associated with weakened cohesion in grooming networks and higher rates of intense aggression. We tested the generality of these findings by analyzing data from 105 matrilines across 16 social groups at CNPRC and Emory NPRC (ENPRC), which differ in group size, natal male management, and housing. Using generalized linear models, we found that matrilines with lower mean kinship coefficients showed greater grooming fragmentation, even after accounting for network density. Threshold analyses identified a mean kinship of 0.16 as the point at which grooming cohesion declined most consistently across both centers, highlighting a biologically meaningful level of relatedness for maintaining kin-biased social bonds. Patterns of severe aggression differed by target and center: across both centers, matrilines with lower mean kinship directed proportionally more severe aggression toward kin. However, for aggression toward all group members, lower kinship predicted more severe aggression only at ENPRC; at CNPRC, this effect emerged only when natal male aggression was included. Our results demonstrate that mean matrilineal kinship is a robust indicator of family cohesion and latent social instability across management settings. Nepotistic threshold analysis provides a practical tool for managers to identify matrilines at risk for social fragmentation and implement interventions before intra-family aggression emerges.

In social insects, non-nestmates interactions are typically agonistic and many factors may influence the degree of exhibited aggression. Two of these factors are the physical proximity between nests and the chemical dissimilarity between colonies chemical signatures. We studied a population sample of 43 colonies of Cataglyphis niger ants distributed along a transect of [~]4KM. This geographic distribution allowed us to examine correlations of aggression levels with physical and chemical distances. Ants were collected before mating season, when sexuals (unmated gynes and drones) could be found in nests. In our sample, colonies had either gynes or drones but never both. The presence of sexuals, therefore, was another factor we took into account in our behavioral analyses. Workers from nests with sexuals were more aggressive towards conspecifics than workers from nests where sexuals were absent. We also found those workers to be more vigorously active towards colonies with greater chemical distances, while workers from nests without sexuals were indifferent to chemical distances. We therefore concluded that ants are able to detect differences in chemical dissimilarity, but their aggression levels are mainly determined by other mechanisms. A possible additional mechanism is associative learning and long term memory of the chemical signatures of neighboring colonies. Such learning is supported by our finding that aggression is higher towards neighboring nests, which is in line with the previously reported nasty neighbour effect in Cataglyphis ants. These results suggest that previous experience and learning of neural templates representing neighbors chemical cues is a stronger component than chemical dissimilarity in the mechanisms which determine aggression towards conspecifics in this species. We discuss possible explanations for the observed effect of the presence of sexuals on agonistic behavior and responsiveness to chemical distances.

The vocalizations of many songbirds have been well documented and analyzed, but less is known about the vocal behavior of many non-passerines, including swifts. When flying alone and during aerial displays with conspecifics, Chimney Swifts (Chaetura pelagic) often utter a twitter call consisting of a series of high-frequency chip notes. However, little is known about the possible function(s) of swift flight displays and their twitter call. Our objectives were to record, analyze, and document the aerial behaviors and associated vocalizations of adult Chimney Swifts. We studied in Madison County, Kentucky, where they used abandoned, concrete shelters for roosting and nesting. Camcorders were used to record swift behavior and vocalizations during the 2008 and 2009 breeding seasons (April - September). We examined possible variation in the characteristics of swift vocalizations and the frequency of different aerial behaviors among breeding stages and behavioral contexts. Chimney Swifts engaged in more interactive pair flights during the nest-building/egg-laying stage, when females are likely fertile, and significantly more than during the pre-building and nestling stages, suggesting the possible importance of pair flights in courtship, pair bonding, and mate-guarding. Our results also suggest that V-ing (a raised-wing display) may be important in establishing or maintaining pair bonds because swifts engaged in this behavior more frequently during close chases involving two birds. We separated the typical swift twitter into two bouts: "steady" bouts and "quick" bouts. Mean chip rates were higher for the quick portion of the call, but we found no differences in the use of steady and quick bouts among nesting stages or in different behavioral contexts. Mean chip rates for quick bouts were highest for single birds and lowest for two and three birds, suggesting that twitter calls provide information about a birds location; to help coordinate movements while flying near others (e.g. when foraging and during chases), We were unable to identify individual swifts; such identification would facilitate the investigation of individual variation in call characteristics (e.g. chip rate and steady/quick bout rate) and relationships between and among swifts engaging in different activities and flight displays.

Many animals communicate using sequences of signals, but identifying recurrent, non-random signal combinations remains methodologically challenging. Collocation analyses are increasingly popular approaches for detecting which signals animals combine at rates greater than expected by chance. However, existing methods for animal collocation analysis face several limitations that reduce their statistical rigour: they lack uncertainty estimates, fail to control for non-independence in sampled data, and do not account for inflated family-wise error rates when identifying attraction among many different signal types. These limitations restrict the broader applicability of animal collocation analysis, including preventing robust comparisons of signal combination strength between cohorts (e.g. populations, sexes or age classes). We adapt a novel form of Multiple Distinctive Collocation Analysis using Pearson residuals (MDCA-Pr) that addresses these statistical limitations, and validate its use in animal communication research in three ways: first, using numerous simulated datasets of different sizes and levels of signal recombination; second, using simulated data to evaluate the performance of MDCA-Pr in intercohort comparisons, and third, by demonstrating how MDCA-Pr can be applied to compare the vocal sequences produced by male and female captive-living common marmosets (Callithrix jacchus). MDCA-Pr shows high sensitivity, including at small sample sizes, and generally low false-positive rates, which we further reduce by applying additional criteria for identifying attraction between signals. During intercohort comparisons, MDCA-Pr is conservative, with low false-positive rates, and statistical power increases with sample size. MDCA-Pr is a robust method for evaluating signal attraction in animal communication and enables accurate intercohort comparison of animal signal combinations. Significance StatementBy assessing the performance of MDCA-Pr on simulated animal-like data, we demonstrate that this method reliably detects signal combinations within and across animal cohorts, while overcoming statistical limitations of previous collocation analyses. We present an analytical pipeline for applying MDCA-Pr to animal signal data, including for intercohort comparisons, enabling identification and comparison of combinatorial strategies across entire signal repertoires. We illustrate this approach by comparing call combination strategies of male and female common marmosets when presented with food under experimental conditions, finding similar combinatorial strategies between sexes. MDCA-Pr therefore permits rigorous characterization of animal signal combinatoriality and opens avenues for investigating how demographic, social, and group-level factors influence combinatorial patterns.

Recent approaches to analysing social networks suggest that modeling the edges of the network and using multilevel models will produce more informative estimates. These recent methods have been proposed as a way to better handle the dependency structures of social networks, account for biases in data collection, and retain uncertainty when making inferences about social network structures. We find that they have the potential to also effectively handle unmeasured variables that act as statistical confounds in social network analysis. Using simulated data, we highlight that static social network analyses can be used to identify patterns in social networks, but generally cannot be used to identify the underlying mechanisms behind the patterns. To identify mechanisms, we show that taking a dynamic approach and using edge-based models with additive and multiplicative random effects provides a means to identify mechanisms even when statistical confounds are present. Additive and multiplicative random effects also provide information about social structures not captured by the predictors, facilitating exploratory analysis. We suggest that a keep-it-maximal approach for random effects structures is beneficial for edge-based multilevel models of social networks, and that such approaches can be particularly effective when there are unmeasured variables that are not captured by model predictors.

Mother-daughter relationships are central to social organization in rhesus macaques, providing the foundation for kin familiarity, affiliative bias, and intergenerational rank inheritance. Understanding how these bonds are structured is therefore important for identifying the processes that contribute to matrilineal cohesion and for anticipating risks of social instability and matriline fragmentation in captive groups. We studied 141 dam-daughter dyads in large, captive groups of rhesus macaques, using generalized linear models to examine associations between demographic variables and affiliative behaviors, and a multivariate clustering approach to characterize how these behaviors combine into distinct relationship types. Our analyses identified eight distinct dam-daughter relationship types defined by combinations of three behavioral domains: grooming, spatial closeness, and agonistic support. Generalized linear models showed that demographic variables had domain-specific effects, with family size, age gaps, and dam age differentially associated with grooming, proximity, and support. These patterns were reflected in the clustering analysis, in which dyads differed not only in overall levels of behavior but also in how behaviors combined within dyads. For example, some dyads exhibited high grooming and support despite low spatial proximity, whereas others showed consistently high expression across all domains. Together, these results demonstrate that dam-daughter bonds are multidimensional and structured through the combination of multiple behavioral domains influenced by demographic and life-history factors. Because these dyads scaffold interactions among close kin, variation in dam-daughter bond structure may influence the development and stability of broader matrilineal relationships. From an applied perspective, considering multiple behavioral domains when assessing social relationships can help identify dyads that may warrant closer monitoring and inform management strategies to support matrilineal cohesion and reduce the risk of social instability in captive groups.

In social species, maternal social relationships, in addition to direct care, impact offspring survival but much of what we know about these effects comes from studies of obligately social and cooperatively breeding species. Yellow-bellied marmots (Marmota flaviventer) are a facultatively social species whose social groups vary in composition, size, and cohesiveness. This natural variation in sociality and cooperative breeding behavior makes yellow-bellied marmots an ideal species within which to study the effects of maternal affiliative and agonistic social behavior on offspring. We used social network analysis to investigate the relationship between maternal social connectivity and integration on offspring summer and yearly survival, with the hypothesis that offspring with more affiliative mothers are more likely to survive than the offspring of more agonistic mothers. However, we found the inverse to be true: pups born to mothers who received more affiliative interactions were less likely to survive while the offspring of mothers who were more highly integrated into agonistic networks had enhanced survival. Overall, maternal social network measures were positively and negatively correlated with offspring survival, indicating that pups are influenced by their mothers social world, often in contradictory ways. Relative predation risk and colony location also mediated the effects of social relationships on pup survival. This study contributes to a small but growing body of work that demonstrates that specific attributes of sociality have specific consequences and that by adopting an attribute-focused view of sociality we are better able to understand how environmental conditions mediate the costs and benefits of sociality. Lay SummaryMaternal social relationships can impact offspring survival but much of what we know about these effects comes from studies of obligately social species. In faculatively social yellow-bellied marmots we found that pups born to mothers who received more affiliative interactions were less likely to survive while the offspring of mothers who were more highly integrated into agonistic networks had enhanced survival. Overall, pups are influenced by their mothers social world, often in contradictory ways.

Behavioural responses are among the fastest ways for wild animals to respond and adapt to environmental change. In breeding birds, nest defence behaviour is particularly important, as it directly influences reproductive success. However, the flexibility of this behaviour, and its links to environmental conditions and fitness, remain poorly understood. Here, we investigate the repeatability of flight initiation distance (FID) - a proxy for nest defence behaviour - in Common gull (Larus canus) breeding pairs within a seabird colony. We assess how consistent individual differences in FID relate to nesting site selection and fitness-related traits. We find that FID is strongly repeatable at the nest level (R = 0.50), indicating consistent behavioural differences among breeding pairs. Moreover, "bolder" pairs tend to nest at greater heights and in areas with higher conspecific density compared to "shier" pairs. Finally, our results suggest that different behavioural types may achieve similar fitness outcomes by selecting nesting sites that match their behavioural types.

Colonies of social Hymenoptera are usually groups of closely related females, in which the dominant female(s) is specialized for reproduction and subordinate females care for immature offspring. Kin selection is thought to be the main factor that supports social cohesion. We have discovered a simple society of the bee Ceratina chalybea with an average of 4.68 colony members that cannot be maintained by kin selection alone. These colonies consisted of old reproductive female, young adults and provisioned brood cells. About half of young adults are unrelated to the old female, and almost all of the young adults are male. The old female provisions new brood cells, while continuing to feed young adult offspring. As young adults do not perform demanding or risky activities, they incur little or no cost, but they do benefit from the food they obtain from the old female.

O_LISocial structure and individual sociality impact a wide variety of behavioural and ecological processes. Although it is well known that changes in the physical and social environment shape sociality, how perturbations govern sociality at a fine spatial scale remains poorly understood. By applying automated experimental treatments to RFID-tracked wild great tits (Parus major) in a field experiment, we examined how individual social network metrics changed when food resources and social stability were experimentally manipulated at the within-group spatial scale. C_LIO_LIFirst, we examined how individual sociality responds when food resources changed from a dispersed distribution (50m apart) to a clustered distribution (1m apart). Second, we tested how sociality changed when individuals were restricted to feeding in a manner that mimics assortative behaviour within flocks. Third, we tested the effects of experimentally manipulating the stability of these social groupings. Finally, we returned the feeders to the original dispersed distribution to test whether effects carried over. C_LIO_LIRepeatability analyses showed consistent differences among individuals in their social phenotypes across the various manipulations; dyadic association preferences also showed consistency. Nevertheless, average flock size and social centrality measures increased after the food was clustered. Some of these metrics changed further when birds were then forced to feed from only one of the five clustered feeders. There was some support for group stability at individual feeders also impacting individual social network metrics: increase in flock size was more pronounced in the stable than the unstable group. Most of the differences in sociality were maintained when the food distribution returned to the dispersed pattern, and this was caused primarily by the change in resource distribution rather than the social manipulation. C_LIO_LIOur results show that perturbations in the access to resources and social group stability can change sociality at a surprisingly fine spatial scale. These small-scale changes could arise through a variety of mechanisms, including assortative positioning within groups due to, for instance, similarity among individuals in their preferences for different resource patches. Our results suggest that small-scale effects could lead to social processes at larger scales and yet are typically overlooked in social groups. C_LI

Early life adversity (ELA) causes lasting psychological and behavioral consequences in humans, with parallel stress and fear responses observed in captive animals. How naturally occurring ELA shapes behavior in non-captive animals remains poorly understood. Investigating these effects across socioecological environments is important for identifying the evolutionary pressures shaping early life sensitivities, and determining whether these behavioral syndromes have deep evolutionary roots. Here, we tested the effects of eight forms of ELA on adult behavior using a large dataset (N=313 males, 346 females) from a free-ranging population of rhesus macaques (Macaca mulatta). We measured adult behaviors indicative of stress and the tenor of social interactions, including agonism, vigilance, self-directed behaviors, and affiliation. Individuals exposed to more ELA received more aggression and less grooming, were more submissive, and were less vigilant. While high status buffered the effects of ELA on grooming, it amplified effects on aggression. Our findings demonstrate that in a large sample of a free-ranging primate, early life environments impact behavior into adulthood. While some behaviors are consistent with patterns in humans and captive animals, suggesting an evolutionarily conserved ELA syndrome, other findings add new insights into the various ways individuals interact with their environment as a function of ELA.

Social parasitism, where one social species parasitically depends on the other for survival and reproduction, is a highly successful life history strategy, especially in the eusocial Hymenoptera. In ants alone, more 400 species of socially parasitic species exist and multiple forms of social parasitism evolved independently and convergently. Yet disentangling the evolutionary history of obligate social parasitism is challenging. Identifying species that inform the transition from eusocial toward socially parasitic behavior is crucial for understanding the underlying co-evolutionary processes. Here, we report the first case of mixed colonies involving four predominantly free-living Temnothorax ant species from the western United States. Three Temnothorax species supplement their worker force with brood from the nests of their four congeners. We suggest, based on these observations and other published evidence, that this facultative dulotic behavior may have resulted from territorial contests due to limited nest sites. Socially parasitic behavior is not present in all populations across the species distribution ranges, however in populations where this behavior was observed, it is also associated with significant increases in interspecific aggression. These four species of Western US Temnothorax ants represent a particularly interesting case of social parasitism, because the presence of between-population behavioral variation provides a powerful system to test hypotheses about the ecological and behavioral conditions underlying the evolutionary transition from eusocial to socially parasitic behavior.

In many cooperatively breeding species non-breeding individuals help to rear the offspring of breeders. The physiological mechanisms that regulate such cooperative helping behavior are poorly understood, but may have been co-opted, during the evolution of cooperative breeding, from pre-existing mechanisms that regulated parental care. Key among these may be a role for prolactin. Here we investigate whether natural variation in circulating prolactin levels predicts both parental and helper contributions to nestling provisioning in cooperatively breeding white-browed sparrow weavers, Plocepasser mahali. In sparrow weaver groups, a single dominant pair monopolize reproduction and non-breeding subordinates help with nestling feeding. We show that: (i) among parents, dominant females feed nestlings at higher rates, make longer provisioning visits, and have higher prolactin levels than dominant males; and (ii) among subordinates, engaged in cooperative helping behavior, those within their natal groups feed nestlings at higher rates and have higher prolactin levels than immigrants. Accordingly, continuous variation in prolactin levels positively predicts nestling-provisioning rates and mean provisioning visit durations when all bird classes are combined. These relationships are principally driven by differences among bird classes in both circulating prolactin levels and provisioning traits. The more limited within-class variation in prolactin and provisioning traits were not evidently correlated, highlighting a likely role for additional mechanisms in the fine-scale regulation of care. Our findings broadly support the hypothesis that parental care and cooperative helping behavior are regulated by a common underlying mechanism and highlight the need for experimentation to now establish the causality of any role for prolactin.

Maximising reproductive success is crucial to animal production systems, particularly in meeting global demands for animal products and improving commercially important traits. However, while social interactions and mating strategies are known to influence reproductive success in wild populations, their consideration in agricultural systems remains limited. Using an interdisciplinary framework that combines concepts from behavioural ecology and quantitative genetics in an animal breeding context, we investigated the role of sperm limitation and polygynous mating strategies (female polyandry, male monopolisation of females and male polygamy) in limiting female reproductive success in farmed Pekin ducks (Anas platyrthynchos domestica). We assessed the impact of these behaviours on chick production and quantified their genetic and environmental (co)variance. Our results revealed that the number of dam mates positively influenced chick production in female ducks. However, contrary to our expectation, skew in chick paternity (our measure of male monopolisation) was associated with increased female chick production, challenging the hypothesis that male monopolisation limits the sperm available to females and reduces their reproductive success. We found no evidence that male polygamy led to decreased female chick production. Genetic analysis revealed that female mate number and reproductive skew exhibit genetic variance, providing opportunities for targeted selection to enhance chick production. However, there was a negative genetic association between female polyandry and skew in chick paternity, suggesting a trade-off between these traits that would need to be considered in future selection programmes. Our findings highlight how concepts from behavioural ecology can be incorporated into breeding programmes, providing new opportunities to develop effective and sustainable breeding strategies.

Cooperative breeding is widely reported across the animal kingdom. In birds, it is hypothesised to be most common in altricial species (where chicks are dependent on parental care in the nest after hatching), with few described cases in precocial species (where chicks are more independent immediately after hatching). However, cooperative breeding may also be more difficult to detect in precocial species and therefore has been overlooked. In this study, we investigate whether vulturine guineafowl (Acryllium vulturinum)--which have precocial young--breed cooperatively and, if so, how care is distributed among group members. Using data collected from colour-banded individuals in one social group of vulturine guineafowl over three different breeding seasons, we found that multiple females can attempt to reproduce in the same breeding season. Broods had close adult associates, and most of these associates exhibited four distinct cooperative breeding behaviours: babysitting, within-group chick guarding, covering the chicks under the wings and calling the chicks to food. Further, we found that offspring care is significantly male-biased, that non-mother individuals provided most of the care each brood received, that breeding females differed in how much help they received, and that carers pay a foraging cost when providing care. Our results confirm that vulturine guineafowl are cooperative breeders, which they combine with an unusual plural-breeding social system. Our study also adds to growing evidence that cooperative breeding may be more widespread among species with precocial young than previously thought, thereby providing a counterpoint to the altriciality-cooperative breeding hypothesis.

Agonistic behaviours are widely observed across multiple taxa and are critical in shaping hierarchies, influencing resource acquisition, survival, and reproductive success. Individuals often alter their behaviour in response to the traits of others, referred to as indirect effects. Individuals also differ in their mean behavioural responses, referred to as direct effects. The combination of indirect and direct effects produce the observed social interactions. Importantly, these effects are typically measured on isolated parts of the full sequence of behaviors and traits expressed during social interactions. Here, we used house crickets, Acheta domesticus, to investigate how direct and indirect effects shape behaviors and traits across an agonistic interaction. We found that the probability of initiating aggression, but not contact, was influenced by both direct and indirect effects independent of mass. Amplitude, peak frequency, and pulse duration of stridulations occurring during agonistic interactions were influenced by direct effects but were not strongly influenced by indirect effects. These results demonstrate that the strength of indirect and direct effects vary over the course of an agonistic interaction and differentially affect the specific components of these interactions. Understanding when and how these effects are important is necessary for understanding agonistic behaviour and its evolution.

For many group living species, vocal signals are a vital form of communication needed to coordinate social behaviours. Investigating these processes first requires a detailed description of the species vocal repertoire. White-nosed coatis (Nasua narica), which forage and move together in forest habitats, are thought to rely on vocalisations to coordinate movements and maintain group cohesion. However, quantitative studies of their vocal repertoire are lacking. We examined the vocal repertoire of white-nosed coatis from wild populations in Panama and Arizona, USA, to gain a more comprehensive view of their calling behaviours. By combining traditional acoustic analyses with an unsupervised approach based on spectrogram structure, we characterised the diversity of calls in this species and described the temporal and structural features of their vocalisations. We identified 19 call types, with some of these calls emitted in multi-syllable call sequences or in fast succession. We found variability in call rates among group members, which may be driven by differences in social status within the group. In addition, our results indicate that white-nosed coatis likely have individually-recognisable vocalisations. This study provides a foundational description of the white-nosed coati vocal repertoire, laying the groundwork for future research on vocal communication in this species.

Sexual production in social insects marks the peak of colony development, yet the mechanisms regulating it remain unclear. We investigated the role of brood in colony development, worker reproduction, and sexual production in Bombus impatiens. While larvae are known to reduce worker egg-laying and enhance the queens reproductive inhibition, these effects were previously tested only in small groups. We manipulated brood size in full-sized, young colonies by doubling or removing brood and monitored development. Colonies with doubled brood produced significantly more gynes, independent of the number of workers, while reduced-brood colonies exhibited a non-significant increase in male production that was driven by colony size. Worker ovary activation was lower in double-brood colonies, with no change in aggression. A follow-up experiment directly testing the effect of colony size showed that higher worker density led to higher ovary activation in workers but did not affect sexual production. These results suggest that brood strongly influences colony development and sexual production, possibly reflecting an extended phenotype of the queen, whereas worker ovary activation appears to be a more flexible process influenced by either brood presence or colony size. Understanding brood dynamics may be key to understanding the evolution of female castes in social insects.

Conspecific brood parasitism (CBP) has been reported in many altricial avian species, yet its prevalence and underlying behavioural mechanisms remain poorly understood. We studied CBP in the barn swallow (Hirundo rustica), a species in which conspecific brood parasitism has been reported. We conducted parentage analysis on 1945 barn swallow broods involving 7816 offspring. Samples were collected over 12 breeding seasons at 5 colonies/populations. Contrary to expectations, we identified only six cases of CBP (0.3 % of broods). By identifying all individuals involved, i.e. the parasitic females, the female hosts and the males that fathered the parasitic eggs, we determined these cases of CBP resulted most likely from either a failed nest take-over (three times), the disappearance of a female partner or a disruption caused by researchers while only one case could be interpreted as a result of females mixed reproductive tactic. Based on a review of the literature on CBP in seven other Hirundinidae, we conclude that the only reliable evidence for CBP comes from cliff swallows (Petrochelidon pyrrhonata). Studies on other species either failed to identify the parasitic females or do not present sufficient evidence supporting the occurrence of CBP. Several studies relied on the appearance of two eggs in a nest within 24 hours to conclude that CBP occurred. However, based on the parentage analysis, we show that CBP only occurred in one out of 11 such cases in our barn swallow data. Our findings highlight that CBP is rare in our barn swallow populations, and have been likely overestimated in other studies. We emphasize the importance of frequent nest checks and rigorous genetic validation in CBP research. Overall, our results challenge existing assumptions about the prevalence of CBP and provide insights into the behavioural mechanisms that lead to CBP, with ecological and evolutionary implications.