Early arrival is not associated with more extra‐pair fertilizations in a long‐distance migratory bird

When assessing the benefits of early arrival date of migratory birds, a hidden and often ignored component of males’ fitness is the higher chance of early‐arriving birds to obtain extra‐pair fertilizations. Here we investigated how extra‐pair paternity might affect the relationship between male arrival date and number of fertilizations in a model study system, the European pied flycatcher Ficedula hypoleuca. For this purpose, we sampled and genotyped breeding pairs, unpaired males and offspring (including embryos from unhatched eggs when possible) of a Dutch pied flycatcher population. Detailed information on arrival date of males, egg laying date of their social mates and nest success was also recorded. Early‐arriving males had early‐laying females and males with early‐laying females had a higher probability of siring extra‐pair eggs and obtain more fertilizations. However, male arrival date alone did not correlate with the probability to gain extra‐pair paternity and neither to the amount of fertilized eggs. Both early‐ and late‐arriving males had a higher probability of losing paternity in their own nest compared to birds with an intermediate arrival date. Finally, late‐arriving males were more likely to remain unpaired but, interestingly, a few of these birds obtained paternity via extra‐pair copulations. Because earlier arrival date did not lead to more extra‐pair fertilizations and because such relationship seems to be driven mainly by the female's laying date, we conclude that the contribution of extra‐pair paternity to the overall fitness benefits of early male arrival date is relatively small.     

Extra‐pair mating in a socially monogamous and paternal mouth‐brooding cardinalfish

Many vertebrates form monogamous pairs to mate and care for their offspring. However, genetic tools have increasingly shown that offspring often arise from matings outside of the monogamous pair bond. Social monogamy is relatively common in coral reef fishes, but there have been few studies that have confirmed monogamy or extra‐pair reproduction, either for males or for females. Here, long‐term observations and genetic tools were applied to examine the parentage of embryos in a paternally mouth‐brooding cardinalfish, Sphaeramia nematoptera. Paternal care in fishes, such as mouth‐brooding, is thought to be associated with a high degree of confidence in paternity. Two years of observations confirmed that S. nematoptera form long‐term pair bonds within larger groups. However, genetic parentage revealed extra‐pair mating by both sexes. Of 105 broods analysed from 64 males, 30.1% were mothered by a female that was not the partner and 11.5% of broods included eggs from two females. Despite the high paternal investment associated with mouth‐brooding, 7.6% of broods were fertilized by two males. Extra‐pair matings appeared to be opportunistic encounters with individuals from outside the immediate group. We argue that while pair formation contributes to group cohesion, both males and females can maximize lifetime reproductive success by taking advantage of extra‐pair mating opportunities.     

Extra‐pair offspring are less heterozygous than within‐pair offspring in American redstarts Setophaga ruticilla

The vast majority of bird species are socially monogamous; however, extra‐pair paternity is nearly ubiquitous and a number of theories have been proposed to explain the prevalence of this mixed mating strategy. Here, we test the genetic compatibility hypothesis – the idea that females seek extra‐pair copulations with males whose genes are more compatible with her own. For this study, we examined eight years of paternity data (2004–2011) from a Nearctic‐Neotropical migratory bird, the American redstart Setophaga ruticilla, breeding in southeastern Ontario, Canada. We predicted that females paired with genetically similar males (higher relatedness) would be more likely to produce extra‐pair offspring and that extra‐pair offspring would have higher levels of heterozygosity than within‐pair offspring. Alternatively, because this population experiences high levels of immigration, females may produce extra‐pair offspring with more genetically similar males because of the potential for outbreeding depression. Using five highly variable microsatellite markers, we examined patterns of relatedness among social pairs as well as measures of offspring heterozygosity. In contrast to our predictions, we found no difference in relatedness between social pairs where the females produced extra‐pair offspring and social pairs where the females produced only within‐pair offspring. However, extra‐pair offspring were significantly less heterozygous than within‐pair offspring. Together, these findings suggest that females a) are not engaging in extra‐pair fertilizations based on relatedness to their social mate and b) appear to be mating with extra‐pair males that are more genetically similar to themselves. We suggest there may be benefits for females to mate with genetically similar extra‐pair males in highly outbred populations with high rates of immigration, such as for maintaining co‐adapted gene complexes or genes coding for local adaptations.     

Age‐dependent changes in infidelity in Seychelles warblers

Extra‐pair paternity (EPP) is often linked to male age in socially monogamous vertebrates; that is, older males are more likely to gain EPP and less likely to be cuckolded. However, whether this occurs because males improve at gaining paternity as they grow older, or because “higher quality” males that live longer are preferred by females, has rarely been tested, despite being central to our understanding of the evolutionary drivers of female infidelity. Moreover, how extra‐pair reproduction changes with age within females has received even less attention. Using 18 years of longitudinal data from an individually marked population of Seychelles warblers (Acrocephalus sechellensis), we found considerable within‐individual changes in extra‐pair reproduction in both sexes: an early‐life increase and a late‐life decline. Furthermore, males were cuckolded less as they aged. Our results indicate that in this species age‐related patterns of extra‐pair reproduction are determined by within‐individual changes with age, rather than differences among individuals in longevity. These results challenge the hypothesis—based on longevity reflecting intrinsic quality—that the association between male age and EPP is due to females seeking high‐quality paternal genes for offspring. Importantly, EPP accounted for up to half of male reproductive success, emphasizing the male fitness benefits of this reproductive strategy. Finally, the occurrence of post‐peak declines in extra‐pair reproduction provides explicit evidence of senescence in infidelity in both males and females.     

Age‐dependent trajectories differ between within‐pair and extra‐pair paternity success

Reproductive success is associated with age in many taxa, increasing in early life followed by reproductive senescence. In socially monogamous but genetically polygamous species, this generates the interesting possibility of differential trajectories of within‐pair and extra‐pair siring success with age in males. We investigate these relationships simultaneously using within‐individual analyses with 13 years of data from an insular house sparrow (Passer domesticus) population. As expected, we found that both within‐ and extra‐pair paternity success increased with age, followed by a senescence‐like decline. However, the age trajectories of within‐ and extra‐pair paternity successes differed significantly, with the extra‐pair paternity success increasing faster, although not significantly, in early life, and showing a delayed decline by 1.5 years on average later in life compared to within‐pair paternity success. These different trajectories indicate that the two alternative mating tactics should have age‐dependent pay‐offs. Males may partition their reproductive effort between within‐ and extra‐pair matings depending on their current age to reap the maximal combined benefit from both strategies. The interplay between these mating strategies and age‐specific mortality may explain the variation in rates of extra‐pair paternity observed within and between species.     

Mating strategies in dominant meerkats: evidence for extra‐pair paternity in relation to genetic relatedness between pair mates

Rates of extra‐pair paternity (EPP) have frequently been associated with genetic relatedness between social mates in socially monogamous birds. However, evidence is limited in mammals. Here, we investigate whether dominant females use divorce or extra‐pair paternity as a strategy to avoid the negative effects of inbreeding when paired with a related male in meerkats Suricata suricatta, a species where inbreeding depression is evident for several traits. We show that dominant breeding pairs seldom divorce, but that rates of EPP are associated with genetic similarity between mates. Although extra‐pair males are no more distantly related to the female than social males, they are more heterozygous. Nevertheless, extra‐pair pups are not more heterozygous than within‐pair pups. Whether females benefit from EPP in terms of increased fitness of the offspring, such as enhanced survival or growth, requires further investigations.     

Feathers,suspicions, and infidelities: an experimental study on parental care and certainty of paternity in the blue tit

Theoretical models on parental care predict that males should decrease their parental effort when paternity is in doubt. Males may use some cues to assess their certainty of paternity, and try to avoid rearing offspring sired by extra‐pair males. We have previously reported in a socially monogamous passerine, the blue tit (Cyanistes caeruleus), that males decorate their nests with feathers, and that when this ornament is manipulated, males appear to have suspicions about the presence of an intruder male. Here, we decrease the male's certainty of paternity through experimental feather supplementation to analyse whether the outcome of our experiment supports the assumptions of the parental care theory. Male C. caeruleus responded to the feather supplementation experiment by reducing their parental investment (feeding frequency and nest defence) in comparison with control males. The occurrence of extra‐pair offspring in experimental nests was double than that in controls. This suggests that the manipulation was successful not only in altering males' perceived paternity, but also, indirectly, the actual paternity. Furthermore, males that gained extra‐pair young also had a higher than average probability to lose paternity in their nest, which may imply that male C. caeruleus faced a trade‐off between obtaining extra‐pair fertilizations and maintaining paternity in their own nest. Overall, this study supports the idea that males are prone to decrease their parental effort when they perceive that the risk of losing paternity is high. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 552–561.     

Lack of evidence for improved immune response of extra‐pair nestlings in collared flycatcher Ficedula albicollis

Extra‐pair paternity is common in many socially monogamous bird species. Increasing evidence suggests that extra‐pair copulations are female‐driven, but benefits for females mating outside social pair‐bonds are still poorly understood. The most influential explanation, “good genes” hypothesis, states that females mated socially with low quality males, engage in extra‐pair copulations to obtain genetic benefits for their progeny. According to this model, enhanced performance of extra‐pair offspring is expected. Here, based on 4‐year study of collared flycatcher Ficedula albicollis, we compared the condition of extra‐pair and within‐pair young. We found no difference in immune response and body size between maternal half‐siblings raised in the same nests. Additionally sex ratio was not biased among extra‐pair nestlings, and paternity was not associated with hatching rank. Our results failed to reveal “good genes” effects in the studied population. These effects might be hard to detect, but other hypotheses should also be studied more thoroughly in the future.     

Experimental evidence that brighter males sire more extra‐pair young in tree swallows

Across taxa, extra‐pair mating is widespread among socially monogamous species, but few studies have identified male ornamental traits associated with extra‐pair mating success, and even fewer studies have experimentally manipulated male traits to determine whether they are related directly to paternity. As a consequence, there is little experimental evidence to support the widespread hypothesis that females choose more ornamented males as extra‐pair mates. Here, we conducted an experimental study of the relationship between male plumage colour and fertilization success in tree swallows (Tachycineta bicolor), which have one of the highest levels of extra‐pair mating in birds. In this study, we experimentally dulled the bright blue plumage on the back of males (with nontoxic ink markers) early in the breeding season prior to most mating. Compared with control males, dulled males sired fewer extra‐pair young, and, as a result, fewer young overall. Among untreated males, brighter blue males also sired more extra‐pair young, and in paired comparisons, extra‐pair sires had brighter blue plumage than the within‐pair male they cuckolded. These results, together with previous work on tree swallows, suggest that extra‐pair mating behaviour is driven by benefits to both males and females.     

Female collared flycatchers choose neighbouring and older extra‐pair partners from the pool of males around their nests

Extra‐pair copulation is common among passerine birds. Females might engage in this behavior to obtain direct or indirect benefits. They may choose extra‐pair males with larger ornaments, especially if they are costly to produce. Here we studied extra‐pair paternity in the collared flycatcher. Genetic analysis allowed us to identify the presence or absence of extra‐pair young in the focal nests, and to identify extra‐pair fathers. We also identified potential males available as extra‐pair sires around the nests of females who had extra‐pair young. First, we tested the relationship between paternity in own nest and ornament size (wing patch and/or forehead patch), morphological traits and age of social males and females. Second, we compared the same suite of traits among social mates, extra‐pair males and all potential extra‐pair mates. Finally, we investigated the effect of the size of ornaments on the distance between the social nest and that of nest the extra‐pair father. Contrary to our prediction, males with larger ornaments and longer wings lost more paternity in their nests. We also found that early breeders lost less paternity in their nests. Extra‐pair males were older and had longer wings than social and potential extra‐pair males. Females mainly obtained extra‐pair mates near their nests but the distance did not vary according to ornamentation. These results could potentially be explained by differences in mate guarding strategy as older males may be more experienced in guarding their mate and attract other females more easily. More data about mate guarding and prospecting are needed to increase our understanding of mechanisms underlying the extra‐pair paternity in birds.     

Are extra‐pair males different from cuckolded males? A case study and a meta‐analytic examination

Traditional models for female extra‐pair matings assume that females benefit indirectly from extra‐pair mating behaviour. Under these so‐called adaptive models, extra‐pair males are hypothesized to have more compatible genotypes, larger body size, exaggerated ornaments or to be older than cuckolded males. Alternatively, (‘nonadaptive’) models that consider female extra‐pair matings to be a by‐product posit that female extra‐pair mating can be maintained even if there is no benefit to females. This could happen if, for example, males gained fitness benefits from extra‐pair mating, while female and male extra‐pair mating behaviours were genetically correlated. Extra‐pair males are also expected to be older and larger if this improves their ability to convince or coerce females to mate. We investigated whether a female's extra‐pair mates differed from her cuckolded mate in both genetic and phenotypic traits by analysing data from an insular house sparrow population. We found that extra‐pair males were older than cuckolded males, consistent with both models. However, in contrast to the expectations from from adaptive models, extra‐pair and cuckolded males were of similar genetic relatedness, and hence expected compatibility, with the female, and had comparable body size and secondary sexual traits. We also updated previous meta‐analyses examining differences between extra‐pair and cuckolded males. The meta‐analytic results matched results from our house sparrow case study. Although we cannot completely exclude indirect benefits for females, nonadaptive models may better explain female extra‐pair matings. These neglected alternative models deserve more research attention, and this should improve our understanding of the evolution of mating systems.     

Mate Guarding in Male Dall's Porpoises (Phocoenoides dalli)

Mate guarding, whereby a male closely attends and defends a fertile female from extra‐pair matings, is one mating tactic males of many species use to protect their paternity. Although female defense occurs in many species of terrestrial mammal, comparable examples among cetaceans are largely absent, potentially as a result of the wide dispersion and mobility of females and their prey. Here, we investigate whether the close association of individual male Dall's porpoises with individual females during the breeding season is consistent with mate guarding. As mate guarding is predicted to be costly, and in other taxa is often associated with a reduction in foraging efficiency, we also examine whether males trade‐off this activity with time at depth. Males maintained longer associations and closer distances with female partners than with male ones. They also surfaced in greater synchrony with, and more often approached, their female partners than male ones. In contrast to males with male partners, males paired with females engaged in agonistic interactions with other adult males, and infrequently affiliated with extra‐pair individuals. These data suggest males are actively attempting to maintain their associations with females, while also acting to reduce female extra‐pair copulations and increase their own paternity. Guarding males also undertook shorter dives than non‐guarding males, suggesting that they trade‐off time at depth with guarding. Such a trade‐off is likely to involve a reduction in foraging opportunities, due to a decrease in time spent at foraging depth. Mate guarding in this species may be facilitated by the relatively smaller size and decreased mobility of newly calved, estrous females, particularly if females also benefit from guarding.     

High frequency of extra‐pair paternity in an urban population of Cooper's Hawks

Raptors exhibit some of the highest rates of intra‐pair copulations among birds, perhaps in an attempt by males to reduce the risk of being cuckolded. Indeed, the frequency of extra‐pair fertilizations reported in studies of raptors to date is relatively low (0–11.2%). Socially monogamous Cooper's Hawks (Accipiter cooperii) exhibit one of the highest copulation rates among birds, yet there are no published accounts of extra‐pair copulations (or paternity). We studied a population of Cooper's Hawks in Milwaukee, Wisconsin, during three breeding seasons (2003, 2004, and 2007), examining the possible effects of age (1 yr old vs. ≥ 2 yr old), adult mass, and brood size on the frequency of extra‐pair paternity (EPP). We found that 19.3% of nestlings (N = 27/140) were extra‐pair young (EPY), and 34% of all broods (N = 15/44) had at least one EPY. The sires of the EPY in our study were identified for only two broods, suggesting that floater males may have engaged in extra‐pair copulations with territorial females. We found that brood size was a good predictor of the occurrence of EPP (EPP) in nests, but adult mass and female age were not. To our knowledge, these possible correlates of the occurrence of EPP in raptors had not previously been investigated. Male Cooper's Hawks provide food for females during the pre‐nesting period, and delivery of food is, in contrast to other raptor species, typically followed by copulation. Thus, one possible explanation of the relatively high rates of EPP in our study is that females might accept or even solicit extra‐pair copulations from males other than their mates as a means of maximizing energy intake for egg production. Such behavior might be particularly likely in our study area, i.e., a food‐rich urban setting with a high breeding density of Cooper's Hawks.     

Female Cape sugarbirds (Promerops cafer) modify egg investment both for extra‐pair mates and for male tail length

The differential allocation hypothesis predicts that females should invest more in reproduction when paired with attractive males. We measured egg volume in Cape sugarbirds (Promerops cafer), a sexually dimorphic passerine, in relation to paternity of the offspring and in response to an experimental tail length treatment. We manipulated tail length, after pair formation, but before egg laying: males had their tails either shortened or left unmanipulated. Our manipulation was designed to affect female allocation in a particular breeding attempt rather than long‐term mate choice: males with shortened tails would appear to be signalling at a lower level than they should given their quality. We found that egg volume was smaller in the nests of males with experimentally shortened tails but larger when the offspring were the result of extra‐pair matings. Both these findings are consistent with the differential allocation hypothesis. We suggest that tail length may be used by females as a cue for mate quality, eliciting reduced female investment when breeding with social mates; and with males with shortened tails.     

Occurrence of extra‐pair paternity is connected to social male's MHC‐variability in the scarlet rosefinch Carpodacus erythrinus

Genes of the Major Histocompatibility Complex (MHC) represent an essential component of the vertebrate acquired immune system. In the last decades, the role of MHC genes in mate choice has been subject of particular scientific interest. However, results of studies dealing with this topic in different species are equivocal and mechanisms conducting MHC‐based mate choice are still puzzling. We investigated the impact of MHC class I variability on within‐pair and extra‐pair fertilisation success in a wild population of a socially monogamous passerine bird with considerable rates of extra‐pair paternity, the scarlet rosefinch Carpodacus erythrinus. We found some support for the ‘good‐genes‐as‐heterozygosity model’, as social males of high MHC‐heterozygosity were cheated by their females less frequently than less MHC‐heterozygous males. However, cuckolding males were not more MHC‐heterozygous than the cheated social males, nor were extra‐pair young more MHC‐heterozygous than within‐pair young. We did not find any evidence for mating preferences according to the complementarity model.     

High fidelity: extra‐pair fertilisations in eight Charadrius plover species are not associated with parental relatedness or social mating system

Extra‐pair paternity is a common reproductive strategy in many bird species. However, it remains unclear why extra‐pair paternity occurs and why it varies among species and populations. Plovers (Charadrius spp.) exhibit considerable variation in reproductive behaviour and ecology, making them excellent models to investigate the evolution of social and genetic mating systems. We investigated inter‐ and intra‐specific patterns of extra‐pair parentage and evaluated three major hypotheses explaining extra‐pair paternity using a comparative approach based on the microsatellite genotypes of 2049 individuals from 510 plover families sampled from twelve populations that constituted eight species. Extra‐pair paternity rates were very low (0 to 4.1% of chicks per population). No evidence was found in support of the sexual conflict or genetic compatibility hypotheses, and there was no seasonal pattern of extra‐pair paternity (EPP). The low prevalence of EPP is consistent with a number of alternative hypotheses, including the parental investment hypothesis, which suggests that high contribution to care by males restricts female plovers from engaging in extra‐pair copulations. Further studies are needed to critically test the importance of this hypothesis for mate choice in plovers.     

Correlates of complete brood failure in blue tits: could extra‐pair mating provide unexplored benefits to females?

Behavioural ecologists have for decades investigated the adaptive value of extra‐pair copulation (EPC) for females of socially monogamous species. Despite extensive effort testing for genetic benefits, there now seems to be a consensus that the so‐called ‘good genes’ effects are at most weak. In parallel the search for direct benefits has mostly focused on the period surrounding egg laying, thus neglecting potential correlates of EPC that might be expressed at later stages in the breeding cycle. Here we used Bayesian methods to analyse data collected over four years in a population of blue tits Cyanistes caeruleus, where no support was previously found for ‘good genes’ effects. We found that broods with mixed paternity experienced less brood failure at the nestling stage than broods with single paternity, and that females having experienced complete brood failure in their previous breeding attempt had higher rates of mixed paternity than either yearling or previously successful females. To better understand these observations we also explored relationships between extra‐pair mating, male and female phenotype, and local breeding density. We found that in almost all cases the sires of extra‐pair offspring were close neighbours, and that within those close neighbourhoods extra‐pair sires were older than other males not siring extra‐pair offspring. Also, females did not display consistent EPC status across years. Taken together our results suggest that multiple mating might be a flexible female behaviour influenced by previous breeding experience, and motivate further experimental tests of causal links between extra‐pair copulation and predation.     

Spatial patterns of extra‐pair paternity for spotted towhees Pipilo maculatus in urban parks

The extra‐pair (EP) mating system of birds may be influenced by food resources, such that nutritionally stressed females are unable to pursue EP fertilizations (constrained female hypothesis; CFH), or that females on poor territories acquire EP fertilizations during extra‐territorial forays in search of food (mating opportunity hypothesis; MOH). Edges of urban habitat fragments are sites of apparent high food abundance for spotted towhees Pipilo maculatus, and we used distance to habitat edge in four urban parks in Portland, OR, USA (2004–2006), to test the CFH and MOH. EP paternity was independent of park identity and year; 44% of nests contained EP young and 26% of all young were EP. As predicted by the CFH, EP paternity was more common in nests of long‐tailed (presumably) high quality females. However, independently of tail length, younger females had more EP young than older females, a finding consistent with the MOH. Contrary to predictions of both hypotheses, the probability that a nest contained EP young was highest both at the habitat edge and habitat interior while the proportion of young in nests of EP origin (for nests with EP young) was highest at intermediate distances from habitat edge. We propose that high frequency of EP paternity among females in the interior occurred because, as predicted by the MOH, they ranged more widely in search of food and often encountered EP males. High probability of EP paternity near edges was likely unrelated to female quality. Instead, anthropogenic food sources may have attracted individuals to edges and increased encounters between potential EP mates. Simple opportunity seems likely to account for patterns of EP paternity in spotted towhees, suggesting that human altered environments have the potential to substantially affect EP mating behavior.     

Experimentally altering pre‐breeding sex steroids reduces extra‐pair paternity in female tree swallows

Extra‐pair paternity commonly occurs in many socially monogamous animal species, yet the reasons why females mate with males outside the social pair bond remain poorly understood. Because sex steroids mediate aggressive and sexual behaviors that peak prior to egg laying in female birds, we tested whether they also influence the rate of extra‐pair paternity in nests of female tree swallows (Tachycineta bicolor). In one treatment, we experimentally elevated testosterone (T) using implants containing exogenous T, and in another treatment, we blocked the estrogenic and androgenic actions of T using implants containing 1,4,6‐androstatrien‐3,17‐dione in combination with flutamide (ATD+F). Females with empty implants served as controls. Nests of females treated with T and those with ATD+F were less likely to contain extra‐pair offspring and had a lower proportion of extra‐pair offspring, compared to control females. Treating females with T also delayed clutch initiation dates and disrupted incubation behavior, as found in previous studies, but clutch sizes of T females did not differ from controls. Females treated with ATD+F tended to lay larger clutches than control and T‐treated females, which may be due to their clutch sizes not declining with later initiation dates as found in the T and control treatments; however, after controlling for brood size, ATD+F females produced nestlings that were lighter at day 16 than control females. Although the effect of T on extra‐pair paternity that we observed in tree swallows is consistent with previous studies in female birds, our results demonstrate that blocking the estrogenic and/or androgenic actions of T during pre‐breeding also lowers extra‐pair paternity. Overall, our study suggests that extra‐pair paternity in tree swallows is mediated by sex steroids of females.     

Extra‐Pair Paternity Declines with Female Age and Wing Length in the Pied Flycatcher

Despite many studies of how male characteristics affect paternity in predominantly monogamous birds, relatively little attention has been given to the traits of females that may influence extra‐pair paternity (EPP). However, the occurrence of EPP may be the result of behavioural interactions in which both male and female traits are important for determining the outcome. If EPP is driven mainly by female choice of extra‐pair sires, older, more experienced or larger females would be better able to evade mate guarding tactics and more capable of selecting extra‐pair mates and resisting unwanted suitors. This would be especially noticeable in females paired with unattractive mates. On the other hand, if EPP is driven mainly by male pursuit, we should expect that young, inexperienced or small females would be more exposed to coercive male approaches independently of social mate traits. In a study of an Iberian population of the pied flycatcher Ficedula hypoleuca, we found that EPP affected 38% of the broods and 17% of the nestlings. These values are relatively high, allowing a relatively large number of affected within‐pair mates to be included. We found that EPP is related to both female and male traits although not to any interaction between male and female traits. EPP was higher at nests tended by both younger and short‐winged females and by browner males. Older females may be more experienced and dominant while long‐winged females may be faster fliers, these traits enabling them to avoid extra‐pair copulations, while brown males are less aggressive towards male intruders. In our study population, EPP appears to be caused by male pursuit, which in some cases may overwhelm female attempts to avoid extra‐pair copulations and their social partner's ability to prevent them.