Unusually high levels of extrapair paternity in a duetting songbird with long-term pair bonds

Previous studies suggest that extrapair young are very rare or absent in socially monogamous avian species that produce vocal duets. These results are generally consistent with functional hypotheses suggesting that duets may signal commitment between partners, or aid males as a paternity guard to ensure genetic as well as social monogamy. Additionally, species that exhibit social monogamy with the same partner across multiple breeding seasons tend to exhibit low levels of extrapair paternity, so duetting species that mate for life may be particularly likely to exhibit genetic monogamy. This study examined the social and genetic mating systems of California towhees (Pipilo crissalis), a duetting species thought to have life-long pair bonds. Observation of a color-banded population confirmed that California towhees exhibit long-term social monogamy. Known social families were genotyped at four microsatellite loci with high allelic diversity. Unexpectedly, paternity exclusion indicated that at least 13 of 31 (42%) nests contained extrapair young. All chicks exhibited maternal alleles, but 21 of 81 (26%) young were not the offspring of social fathers. Thus, in contrast to previous work, this study documents high frequencies of extrapair young among socially monogamous duetting birds with long-term pair bonds.     

Land or lover? Territorial defence and mutual mate guarding in the crimson-breasted shrike

Crimson-breasted shrikes produce duets which are used in interactions with neighbours and intruders. We examined two major hypotheses explaining duetting, the territorial defence and mate guarding hypotheses, using playback experiments. The responses of 12 pairs towards solo male, solo female and stereo duet playback were analysed using principal component analysis and ANOVA. The measures of response intensity revealed in most cases highly coordinated responses of the pair partners. Although these joint responses could suggest cooperative territorial defence or mutual mate defence, responses to the treatments differed between males and females in terms of three variables. Females increased their answer rates significantly in response to unpaired female intruders, compared to unpaired male intruders. During duet playback, females directed their responses equally at both intruding pair members. In contrast, males were equally responsive towards unpaired male intruders and intruding pairs, but in the latter case directed their responses at the male pair member. In the presence of unpaired female intruders, males increased their solo song rates, but in the presence of intruding pairs, they increased overlapping rates and duetted with their mates. These divergent responses suggest that females use duets for mate guarding against unpaired females, whereas males use solo songs for mate guarding and both solos and duets in territorial defence.     

No evidence for acoustic mate-guarding in duetting buff-breasted wrens (Thryothorus leucotis)

There are few empirical tests of the acoustic mate-guarding hypothesis for the function of duetting in birds. This hypothesis states that when females are fertile, males initiate many songs or answer most of their mates solo songs to form duets and repel rival males seeking extra-pair copulations. We tested the hypothesis by comparing song initiation and answer rates of males and females in socially monogamous buff-breasted wrens (Throthorus leucotis) during pre-fertile and fertile periods. During pre-fertile periods, males often sang for short periods before being answered by their mates, yet first duets were formed earlier relative to dawn and more duets were given during the dawn chorus on pre-fertile than fertile mornings. Males initiated more songs during pre-fertile than fertile periods, whereas there was no difference between stages in female song initiation rates. The proportion of songs answered by individuals of both sexes did not differ between breeding stages. Other mate-guarding behaviours, such as frequent copulation and maintaining close proximity to mates when fertile, did not appear to be important in this species, as no copulations were observed and there was no difference in the time pairs spent in close proximity when females were fertile or not. Parentage analysis revealed that only 3% of 31 broods had young that were likely the result of extra-pair paternity. These findings do not support the acoustic mate-guarding hypothesis, and suggest that the low rate of extra-pair paternity in buff-breasted wrens was maintained without the use of acoustic or traditional paternity guards.Communicated by R. Gibson     

Mate guarding and copulation behaviour in monogamous and polygynous blue tits: do males follow a best-of-a-bad-job strategy?

This study investigates the importance of mate guarding for males and females in the facultatively polygynous blue tit Parus caeruleus. We present observational data in combination with a paternity analysis using DNA fingerprinting to show that (1) male blue tits guard their mate, since they stay closer to their mate, initiate fewer flights and follow their mate more often during the female's presumed fertile period; (2) polygynous males do not suffer more from lost paternity despite lower mate guarding; (3) in monogamous pairs there is either no relation or a positive relation (depending upon the variable measured) between measures of mate guarding intensity and the proportion of extra-pair young in the nest; and (4) monogamous males that are more often followed by their fertile female suffered less from lost paternity. We conclude that, despite mate guarding, paternity seems to be largely under female control and unattractive males guarding their mate are making the best of a bad situation. Experimental evidence is provided showing that when males were temporarily removed from their territory, their mate suffered from increased harassment from neighbouring males that intruded in the territory and tried to copulate with the female. Almost all of these copulation attempts were unsuccessful because females refused to copulate. We conclude that mate guarding may be beneficial for females because harassment by neigbouring males is prevented.     

Duetting and mate-guarding in Australian magpie-larks (Grallina cyanoleuca)

A recently favored hypothesis is that duetting in birds has a mate-guarding function: a male responds vocally to his partner’s song, thereby forming a duet that repels males who are attracted to her song. Previous studies have not provided unambiguous tests of the mate-guarding hypothesis because: (1) the probability of a male answering his partner’s song has not been shown to increase specifically when the female is fertile, and (2) the probability of a male answering his partner’s song has not been assessed separately from simply a higher song initiation rate. We investigated extra-pair paternity, mate-guarding, and duetting in the socially monogamous Australian magpie-lark (Grallina cyanoleuca). DNA fingerprinting revealed that 3% of young were the result of extra-pair paternity, and we found that males guarded fertile females by staying close to them. However, males did not initiate songs at a higher rate when females were fertile and actually reduced their probability of replying to female song during this period. We conclude that although male magpie-larks did guard fertile females in an attempt to prevent extra-pair copulations, they did not use duetting for this purpose. Received: 10 May 1999 / Received in revised form: 27 September 1999 / Accepted: 2 October 1999     

The behavioral regulation of monogamy in gibbons (Hylobates muelleri)

Summary Responses of mated individuals to playbacks of the songs of solitary females and males permit evaluating the behavioral mechanisms maintaining monogamy in gibbons. When female songs are played back from the centers of their ranges, mated female gibbons typically initiate duets and group approaches toward playback sites. Female songs played back from range boundary locations elicit duetting responses. Responses to solitary female songs do not differ from responses to song duets used by established mated pairs to mediate patterns of intergroup spacing. Mated males lead silent group approaches toward the sites of male song playbacks. These results suggest that range defense by female gibbons forces males into accepting monogamous mating relationships and that monogamy in gibbons is regulated by intersexually-supported, intrasexual aggression.     

Extra-pair paternity and tail ornamentation in the barn swallow Hirundo rustica

Females of socially monogamous species may copulate with attractive non-mates to obtain access to the genes of such males, and a preference for attractive copulation partners may result in sexual selection. Extra-pair copulations are common in the socially monogamous barn swallow Hirundorustica, and a 2-year study of paternity using multi-locus DNA fingerprinting demonstrated that 33% of 63 broods and 28% of 261 offspring were sired by extra-pair males. The frequency of extra-pair offspring within broods was highly skewed with the majority of all broods having either no extra-pair offspring or only extra-pair offspring. Individual pairs were consistent in their frequency of extra-pair paternity among broods, and the repeatability of extra-pair paternity of multiple broods of the same female was statistically significant. The proportion of extra-pair offspring was negatively related to the tail length of the male attending the nest. Behavioural observations showed that extra-pair fertilizations were more likely in broods raised by females that had been observed to engage in extra-pair copulations. The frequency of extra-pair offspring was unrelated to the intensity of two male paternity guards, mate guarding and the rate of intra-pair copulations. In an analysis of extra-pair paternity and male parental care in different broods of the same male, male barn swallows fed their offspring relatively less frequently if the brood contained more extra-pair offspring. Therefore, female barn swallows pursue extra-pair copulations with attractive males, which may result in sexual selection, even though extra-pair paternity is costly for females due to the reduction of paternal care by their social mates. Received: 24 January 1997 / Accepted after revision: 2 August 1997     

Territory defence in tropical birds: are females as aggressive as males?

Much of our knowledge concerning the functions of territorial behaviour and how territories are defended by individuals comes from research on birds. The vast majority of this work has focused on temperate zone breeding territoriality in which territories are defended most obviously by males. Our understanding of the female role in territory defence is limited because they are less conspicuous and much harder to observe. We studied sex roles in territory maintenance and defence in a duetting, resident neotropical passerine, the white-bellied antbird (Myrmeciza longipes). This species maintains territories and pair bonds year round and both sexes sing and actively participate in territory defence. We performed a series of playback experiments throughout the dry (non-breeding) and wet (breeding) seasons. We exposed territorial pairs to three types of stimuli including: (1) single sex, male only songs, (2) single sex, female only songs, and (3) both sex songs/duets. Contrary to findings for most other tropical species, individuals defended their territories with equal levels of aggression regardless of stimuli. Furthermore, sex roles were very different, with males responding more aggressively than females to all stimuli throughout both seasons. Both males and females consistently responded more aggressively to territorial intrusions during the dry season than during the wet season, likely because food abundance is low in the dry season and territory value is high. Our analysis of duetting behaviour suggests that duets do not serve a significant role in mate guarding, or territory defence.     

Inter-sexual conflicts over copulations in the European starling: evidence for the female mate-guarding hypothesis

Recent studies have suggested that conflicts of interests between the sexes may lead to variation in copulation behavior among pairs. We examined differences in the rate and timing of copulation solicitations and copulations among females of different mating status in the facultatively polygynous starling in an attempt to explain why females copulate repeatedly with their mate. All within-pair copulations were female-solicited indicating that females control copulations in the starling. Before egg laying, females solicited copulations at a high rate (usually more than 2 per hour). In contrast to most other species studied so far, females continued to solicit copulations throughout the egg laying period, and also solicited after egg laying (the latest solicitation occurred when the nestlings were 4 days old). Primary females solicited more copulations than monogamous females both during and after the fertile period. Many copulation solicitations of primary females occurred at the nestbox where their male was singing to obtain an extra female. Both primary and secondary females solicited more copulations after the egg-laying period than monogamous females. A large proportion of female copulation solicitations was refused by the male partner: female solicitation resulted in more male refusals in primary females than in monogamous females. Primary females were more likely to be chased aggressively when they solicited a copulation than monogamous females; most aggressive chases occurred when primary females flew towards their male to solicit copulation when he was singing at another nestbox. Overall, our results demonstrate that there is a conflict over copulation between males and females in polygynous pairs. The conflict presumably relates to the cost of sharing male parental investment: females use copulation solicitation behavior to interrupt their singing males apparently in an attempt to prevent them from becoming polygynous. We present the first empirical evidence that female songbirds use copulation solicitation behavior as a form of mate guarding, often in a non-reproductive context. We did not find a positive relationship between copulation rate during the fertile period and the amount of male parental care as is predicted by the paternity confidence hypothesis.     

Breeding synchrony and paternity in the barn swallow (Hirundo rustica)

The barn swallow (Hirundo rustica) is a socially monogamous passerine which usually breeds in colonies where extra-pair copulations are frequent. Males intensively guard their mates during the female fertile period. Since males are more likely to be available for extra-pair copulations when their mate is not fertile, synchrony in timing of breeding may affect paternity of individual males. In this study, we analysed the change in mate-guarding rate by males in relation to the fertility condition of the female, and the relationships between breeding synchrony and density with paternity in first broods of 52 male barn swallows. Paternity (proportion of nestlings fathered in own brood) was assessed by typing of three highly polymorphic microsatellite loci. Mate guarding by males peaked during the fertile period of their mates. Paternity increased as breeding synchrony in the colony increased. Paternity of barn swallows is positively associated with the degree of exaggeration of male tail ornaments. The relationship between male ornamentation and paternity was partly mediated by an effect of ornament size on breeding synchrony. We suggest that females might delay breeding with low-quality males to enhance their opportunities for being fertilised by high-quality extra-pair males. Received: 16 January 1998 / Accepted after revision: 25 October 1998     

Seasonal variation in the duetting behaviour of rufous-and-white wrens (<Emphasis Type="Italic">Thryothorus rufalbus</Emphasis>)

Seasonal variation in animal signalling behaviour has been well documented and has contributed much to our understanding of male signals. In contrast, we know little about seasonal variation in female signals or signals produced jointly by males and females, such as the vocal duets of birds. Here, we examine how singing behaviour changes in relation to time of year and breeding stage in rufous-and-white wrens (Thryothorus rufalbus), neotropical songbirds where both males and females sing and where breeding partners coordinate songs to produce vocal duets. We recorded a colour-marked population of birds over an extended time period encompassing multiple breeding stages. Across all time frames and breeding stages, males sang at higher rates than females and male solos were more common than duets or female solos. Males and females showed divergent seasonal patterns of singing. Females sang more often early in the year, during the pre-breeding season, and female song tapered off as the breeding season progressed. Duetting followed a parallel pattern, which resulted from females showing less duet responsiveness to their partner’s songs later in the year. Male independent song rate peaked at the onset of the rainy season – a time when females become fertile – and males showed the highest level of duet responsiveness during this period. Our results suggest that early in the year, duets appear to be cooperative displays, functioning in joint territory defence and/or the coordination of breeding activities. When females are fertile, however, increased duet responsiveness by males is consistent with mate or paternity guarding.     

Condition-dependent control of paternity by female purple martins: implications for coloniality

Proposed causal links between extra-pair copulation (EPC) and colony formation in socially monogamous birds hinge on the question of which sex controls fertilizations. We examined in colonial purple martins Progne subis (1) whether EPCs were forced or accepted by females, and (2) the degree to which apparently receptive females were able to obtain EPCs against their mates’ paternity defenses. Paternity analyses of multilocus DNA fingerprinting confirmed previous findings of a marked relationship between age class and extra-pair fertilizations (EPFs), with young males losing paternity of 43% (n = 53) of their putative offspring compared to 4% (n = 85) by old males. All assignable extra-pair offspring were sired by old males, with one male obtaining most EPFs each year. Contrary to the hypothesis that EPCs are forced, EPF frequency within age class did not increase with seasonal increases in the number of males per fertile female. Whereas the male control hypothesis predicted that the male age class that mate-guarded more would be cuckolded less, the reverse was true: young males guarded significantly more intensely. The male age class difference in cuckoldry could not be explained by the possibility that young and inexperienced females (which are usually paired to young males) were more vulnerable to forced copulation because EPFs were unrelated to female age. These findings suggest that females (1) pair with old males and avoid EPCs, or (2) pursue a mixed mating strategy of pairing with young males and accepting EPCs from old males. The receptivity to EPCs by females paired to young males put them in conflict with their mates. Two factors determined the paternity achieved by young males: (1) the relative size of the male to the female, with young males achieving much higher paternity when they were larger than their mates, and (2) the intensity of mate-guarding. Both variables together explained 77% of the variance in paternity and are each aspects of male-female conflict. Given female receptivity to EPCs, mate-guarding can be viewed as male interference with female mating strategies. We conclude that EPCs are rarely or never forced, but the opportunity for females paired to young males to obtain EPCs is relative to the ability of their mates to prevent them from encountering other males. Evidence of mixed mating strategies by females, combined with other features of the martin mating system, is consistent with the female-driven “hidden lek hypothesis” of colony formation which predicts that males are drawn to colonies when females seek extra-pair copulations. Received: 23 March 1995/Accepted after revision: 14 January 1996     

Dominance rank,female reproductive synchrony,and male reproductive skew in wild Assamese macaques

In groups with multiple males, direct mate competition may select for the evolution of dominance hierarchies that sort males into a queue for access to fertile females. The priority-of-access (PoA) model proposed by Altmann in 1962 makes explicit predictions about the resulting paternity distribution based on an interaction between male dominance rank and the overlap of female receptive phases. Here, we investigated whether the logic of the PoA model predicted the distribution of paternity across ranks in a seasonal breeder with high reproductive synchrony over six consecutive mating seasons. We studied 18 males that resided in a group of wild Assamese macaques (Macaca assamensis) in their natural habitat at Phu Khieo Wildlife Sanctuary, Thailand, between 2006 and 2011 with 5 to 13 conceptions per season. We assessed whether mate guarding increased paternity success, described “short-term” deviations from predicted paternity distribution, and examined how these are related to the number of competitors and fertile females. We determined genetic paternity of 43 (93 %) offspring born into the study group and found reproductive skew to be relatively low with 29 % alpha male paternity in accordance with the high degree of female reproductive synchrony observed. Short-term deviations from expected paternity distribution over ranks were not explained by the number of resident males or the number of conceiving females or their interaction. Within the limits of this study, these results suggest that even if males cannot discern female fertile phases, if reproduction is seasonal, and if reproductive synchrony is high, males may also compete directly over access to females.     

Duetting in the subdesert mesite Monias benschi: evidence for acoustic mate defence?

Despite numerous hypotheses proposed for the function of duets, there is currently no consensus as to why males and females should coordinate their songs in such a precise way. There is evidence indicating that duets sometimes serve in territory defence, but additional functions are rarely considered. The mate-defence hypothesis proposes that birds sing in response to their partner's song and the resulting duet repels rivals and may prevent desertion of a partner. We investigated this idea in the subdesert mesite Monias benschi using playback experiments in which we broadcast recordings of solos and duets to single birds and groups. Two predictions of the hypothesis were met: (1) the solo songs of both sexes incited aggressive responses from paired birds of the same sex; and (2) compared to solo songs, pair duets elicited weaker responses from groups and duetting pairs. However, groups responded to male duets with a vigour equal to that with which they responded to male solos. This indicated that the weaker responses of groups to pair duets compared to male solos was a function of the sex rather than number of vocalising birds. Groups responded more strongly to male solos than to either female solos or pair duets, and females' responses were generally weaker than those of males. This may reflect stronger competition among males for mates, due to a male-biased sex ratio in the population. We conclude that song serves similar functions in each sex and that duets may arise through mutual mate defence.     

Do male plumage and song characteristics influence female off-territory forays and paternity in the hooded warbler?

Extra-pair fertilizations are common in many socially monogamous species, and paternity studies have indicated that females may use male vocal performance and plumage ornaments as cues to assess male quality. Female off-territory forays may represent a key component of female choice and male extra-pair mating success, and female foray behaviour is expected to be strongly influenced by indictors of male quality. In this study, we examined how male song and ornamentation affect how often females left their territories, which males they visited and extra-pair paternity in a socially monogamous passerine, the hooded warbler (Wilsonia citrina). We radiotracked 17 females during the fertile period and quantified male vocal performance (song output and rate) and plumage characteristics (size of the black melanin hood and colour of the black hood, yellow cheeks and breast areas). We obtained blood samples and determined paternity at 35 nests including those of 14 females that we radiotracked. Eleven (65%) of the 17 females forayed off-territory, whilst fertile and female foray rate was positively correlated with the number of extra-pair young in the nest. Females that left their territories more frequently were paired with males that sang at a low rate. In addition, extra-pair mates had higher song rates than the social mates they cuckolded (5.3 songs/min vs. 4.4 songs/min). Female off-territory forays or extra-pair paternity were not significantly related to male plumage characteristics. Our results indicate that a high song rate influences both the foray behaviour of a male’s social mate and the likelihood that he will sire extra-pair offspring with neighbouring females.     

Manipulating the perceived opportunity to cheat: an experimental test of the active roles of male and female zebra finches in mate guarding behavior

Birds are commonly sexually promiscuous, which can lead to conflict between the sexes and the evolution of paternity assurance strategies, such as mate guarding. Adaptive explanations for mate guarding have tended to focus on fitness consequences for males, but mate guarding and participation in being guarded is also likely adaptive for females in certain contexts. To better understand the adaptive explanations for mate guarding as well as the observed variation in paternity patterns, it is necessary to explore the relative costs and benefits of guarding (and being guarded) from both the male and female perspective. To investigate these costs and benefits, we conducted an experiment with the Australian zebra finch (Teniopygia guttata) in which we independently varied the perceived opportunity for each member of a captive breeding pair to engage in extra-pair copulation (EPC) solicitation behavior; as an individual’s EPC opportunity increased, the partner’s EPC opportunity remained constant. Our results indicate that, for males, mate guarding intensity increases when their female’s EPC opportunity increases but decreases when their own (i.e., male) EPC opportunity increases. We did not find evidence of flexible female guarding behavior, but we found that females do not evade their partners more as female EPC opportunity increases.     

Sex allocation and paternity in a cooperatively breeding passerine: evidence for the male attractiveness hypothesis?

Sex allocation theory predicts that female birds with high-quality mates will benefit from producing more sons, since sons will inherit their father’s superior traits and enjoy a great reproductive success, whereas females with low-quality mates will benefit from producing more daughters, since the variance in reproductive success among daughters is typically lower. The male attractiveness hypothesis may apply to extra-pair paternity (EPP) because socially monogamous females routinely mate with higher quality males outside the pair bond. We test these predictions using the Tibetan ground tit (Pseudopodoces humilis), a sexually monomorphic, socially monogamous, facultatively cooperative breeder. There was greater variation in actual reproductive success among males than females due to EPP. An excess of sons was detected for bi-parental (i.e., non-cooperative) broods wherein EPP was mainly sired by bi-parental males. The pattern was attributed to male-biased sex ratios produced for both EPP and within-pair offspring within the same broods. The reason for the latter case might be a random allocation of more offspring to sons by the potentially EPP-exposed females that have an inability to control fertilization by specific males. In cooperative broods where EPP mostly resulted from within-group helpers of presumed low-quality, as indicated by their failure in acquiring a social mate, there was a non-significant tendency for EPP offspring to be daughters and for within-pair offspring in the same broods to be unbiased. These results support the EPP-related male attractiveness hypothesis especially in terms of the overproduction of sons. Offspring produced through quasi-parasitism was unbiased towards either sex, suggesting a weak female choiceness with respect to the quality of host males.     

Multiple sexual pigments,assortative social pairing,and genetic paternity in the yellow warbler (Setophaga petechia)

In socially monogamous species, extra-pair paternity may increase the reproductive success of highly ornamented males, mediating the evolution of sexual ornaments. However, ornaments may also attract social mates, and a tradeoff between extra-pair paternity (EPP) and within-pair paternity (WPP) may complicate mating strategies. Further, in many socially monogamous species, females are also ornamented, and the relationship between female ornamentation and patterns of EPP has been neglected. We investigated the patterns of genetic paternity with respect to carotenoid- and melanin-based pigmentation in yellow warblers (Setophaga petechia) of both sexes. We asked whether males face tradeoffs between EPP and WPP, how paternity patterns relate to carotenoid- versus melanin-based pigmentation, and whether less EPP occurs in broods when males and females are assortatively paired. Males faced a tradeoff between EPP and WPP. Moreover, non-additive relationships existed between paternity patterns and the two pigment types in both sexes. Males with high melanin coverage but dull carotenoid pigmentation achieved EPP but lost WPP, whereas males with high levels of both pigment types had high WPP but gained little EPP. A parallel pattern occurred in females. Warblers paired assortatively by pigmentation and EPP was less common in broods when the sexes were assortatively paired by carotenoid pigmentation. Results suggest that the most colorful birds obtain high quality social mates and advance reproductive success through WPP, show that correlations can arise between female ornamentation and patterns of EPP, and also uniquely suggest that social pairing patterns may influence extra-pair mating strategies.     

Mate guarding in the swallowHirundo rustica

Summary The importance of mate guarding by males in the monogamous swallowHirundo rustica was studied by temporarily detaining the males. Mate guarding reduced the frequency of extra-pair copulations and of sexual chases involving female mates. Males participated in sexual chases more frequently if they had a non-fertile female. Neighbouring males of ‘widowed’ females increased their own mate guarding presumably in response to the experimentally increased rate of sexual chases. Neighbouring males with a fertile female increased their mate guarding more than did males with a non-fertile female. Addition of eggs to swallow nests in the post-fledging period of the first brood induced mate guarding by male nest owners. These males also copulated more frequently with their mates than did control males. Neighbouring male swallows responded to the increased mate guarding by showing sexual interest in the guarded females. removal of eggs from swallow nests during the laying period, leaving only one egg in the nest, resulted in reduced nest attendance by females. Male mates responded by increasing their mate guarding intensity as compared to controls, and neighbouring males showed an increased sexual interest in these females.     

Positive association between social and extra-pair mating in a polygynous songbird, the dickcissel (Spiza americana)

In polygynous species, males appear to gain additional offspring by pairing with multiple females simultaneously. However, this may not be true if some females copulate outside of the social pair bond. Polygynous males could experience lower paternity because of trade-offs among gaining multiple social mates, guarding fertility with these mates, and pursuing extra-pair matings. Alternatively, polygynous males could simultaneously gain extra social mates and have high paternity, either because of female preferences or because of male competitive attributes. We tested four predictions stemming from these hypotheses in a facultatively polygynous songbird, the dickcissel (Spiza americana). Unlike most previous studies, we found that males with higher social mating success (harem size) also tended to have higher within-pair paternity and that the number of extra-pair young a male sired increased significantly with his social mating success. Females that paired with mated males were not more likely to produce extra-pair young. In contrast, extra-pair paternity was significantly lower in the nests of females whose nesting activity overlapped that of another female on the same territory. This pattern of mating was robust to differences in breeding density. Indeed, breeding density had no effect on either extra-pair mating or on the association between polygyny and paternity. Finally, nest survival increased with harem size. This result, combined with the positive association between polygyny and paternity, contributed to significantly higher realized reproductive success by polygynous male dickcissels.