Mate choice in the brown thornbill (<Emphasis Type="Italic">Acanthiza pusilla</Emphasis>): are settlement decisions,divorce and extrapair mating complementary strategies?

In socially monogamous birds, females may express mate preferences when they first select a breeding partner, through divorce and subsequent breeding dispersal to a new partner and through extrapair mating. We examined settlement patterns, divorce and breeding dispersal in a sedentary Australian passerine, the brown thornbill (Acanthiza pusilla), in relation to two traits known to influence extrapair paternity (male age and male size). Settlement decisions, divorce and territory switching behaviour were all female strategies that reduced their likelihood of breeding with 1-year-old males. Females preferred to settle in territories with 2+ -year-old males, were more likely to divorce 1-year-old males, and only switched territories if they had an opportunity to form a new pair bond with an old male. In contrast, female settlement and divorce decisions were not influenced by male size. Female thornbills obtain a direct benefit from preferring older males as social mates because breeding success improves with male age in brown thornbills. Nevertheless, divorce rates in this species were low (14% of pair bonds were terminated by divorce), and individuals rarely switched territories following the death of a mate. Both of these mating strategies appeared to be primarily constrained by the distance adults moved to initiate a new pair bond (1–2 territories) and by the limited availability of unpaired older males in the immediate neighbourhood.Communicated by M. Webster     

The pursuit of extra-pair copulations by monogamous female razorbills: how do females benefit?

Summary Monogamous female razorbills Alca torda actively sought extra-pair copulations (EPCs) in mating arenas outside their nesting colony. Females showed marked variation in promiscuity, defined as the number of EPCs they accepted (0–7), and in receptivity, defined as the percentage of EPC opportunities accepted (0%–100%). The opportunity of females to encounter males for EPCs was measured by (a) the time spent in the mating arena, and (b) the guarding effectiveness of their mates. Females appeared to encounter males and accept EPCs independently of opportunity, which suggests that variation in promiscuity and receptivity is caused by differences in the degree to which individual females might benefit from EPCs. I tested predictions of four hypotheses which propose benefits which females could obtain from EPCs: good genes, genetic diversity of offspring, insurance against infertility of mate, and acquisition of a new mate. No evidence was found to support two predictions made exclusively by the good genes hypothesis: (a) paired males did not achieve greater EPC success than unpaired males, and (b) males who were cuckolded did not obtain fewer EPCs than males whose mates avoided EPCs, suggesting that a male's attractiveness to other females does not ensure his own mate's fidelity. A prediction of both the insurance and good genes hypotheses was supported: females (who in this species retain their mates between years) showed similar receptivity to EPCs between years. This finding contradicts the genetic diversity hypothesis which predicts that in species that lay one egg per year, females who refuse EPCs in one year will accept them in the next. The good genes and genetic diversity hypotheses both predict that females who accept EPCs will behave as if to maximize their chances of being fertilized by extra-pair males. Results contradicted this prediction: females who accepted EPCs were more, rather than less receptive to their mates' copulation attempts than were females who did not accept EPCs. This finding is compatible with the insurance hypothesis which only requires females to store the sperm of extra-pair males, without necessarily being fertilized by it. Insurance against male infertility was the only hypothesis whose predictions were not contradicted by any of the results.     

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.     

Female tree swallows (<Emphasis Type="Italic">Tachycineta bicolor</Emphasis>) increase offspring heterozygosity through extrapair mating

Recent attention has focused on genetic compatibility as an adaptive function for why females engage in extrapair mating. We tested the genetic compatibility hypothesis in tree swallows (Tachycineta bicolor) over five breeding seasons using data from ten microsatellite loci. Tree swallows are socially monogamous passerines exhibiting high levels of extrapair paternity. Overall, we found that 47% of offspring were the result of extrapair fertilizations, and 83% of females produced at least one extrapair offspring. Consistently for all years, extrapair offspring were more heterozygous than their maternal half-siblings, which is in accordance with the genetic compatibility hypothesis. The difference was largely caused by the high heterozygosity of extrapair offspring sired by unknown males, suggesting that females are engaging in extrapair copulations with geographically distant males to increase the likelihood of being inseminated by a more compatible mate. Our findings support the idea that postcopulatory mechanisms are important for females when assessing potential sires for their offspring.     

Female choice contributes to offspring fitness in the field cricket,Gryllus bimaculatus (De Geer)

Summary Females of the field cricket, Gryllus bimaculatus, are known to mate non-randomly with respect to male size. The reproductive output of females allowed to choose their mates was compared with that of females allocated mates. Females allowed to choose their mates laid a greater proportion of their available eggs, thereby investing more heavily in reproduction. Female choice did not appear to influence hatching success, suggesting that no short term benefits are derived from non-random mating. However, the offspring of females allowed to choose their mates developed more rapidly and began their own reproductive output before those of females who had been allocated mates. Furthermore, the faster developing offspring of females who chose their mates tended to have a consistantly higher survival rate as well as a lower variance in survival (i.e. less risk of mortality) at adult eclosion. Female choice may therefore contribute to offspring fitness and thus to long term reproductive success. Females allocated large males as mates did not equal those of females allowed to choose their mates, in terms of reproductive output and offspring fitness. This suggests that females may choose their mates with regard to a mixture of characters of which male size is only one.     

Selected polyandry: female choice and inter-sexual conflict in a small nocturnal solitary primate (<Emphasis Type="Italic">Microcebus murinus</Emphasis>)

Sex-specific interests over the maximization of reproductive success lead to an inter-sexual conflict over the optimal mating system in a species. Traditionally, the outcome of this inter-sexual conflict has been studied from the male perspective but it also depends on female mating strategies, such as manipulating the temporal distribution of sexual activity, advertisement, and mate choice. We used a small nocturnal primate, the gray mouse lemur (Microcebus murinus) to determine the relative importance of female mating strategies on the outcome of this conflict in a species where females are solitary during their activity period. We studied their mating behavior over three consecutive annual mating seasons and determined the genetic relationships among more than 300 study animals to quantify individual reproductive success. We found that most females were receptive asynchronously. Females did not exhibit any obvious direct mate choice, probably due to a highly male-biased operational sex ratio and the corresponding costs of choosiness. However, females exercised indirect choice for multiple matings. They mated with 1–7 males up to 11 times during their single night of receptivity. As a result, mixed paternity was common but heavier males sired more offspring, meaning that indirect female choice for superior males cannot be excluded. Females exhibited a mixed mating strategy, avoiding costly direct mate choice but still counteracting male efforts to monopolize mating, successfully increasing genetic variability among offspring. Thus, females had a major influence on the outcome of the inter-sexual conflict despite male monopolization attempts.Communicated by J. Setchell     

Divorce in common murres (Uria aalge): relationship to parental quality

Behavioral precursors of 12 divorces were examined in 30 color-banded pairs of common murres (Uria aalge) over six breeding seasons. Common murres are long-lived seabirds that typically return each year to the same mate and nest site in dense colonies. At least one parent is present continuously from egg lay to chick fledging. Murres, therefore, have considerable opportunities to compare their mates parental behavior with that of several familiar neighbors. Previous reproductive success was lower for divorcing birds than for reuniting pairs. As predicted by the better option hypothesis, there were clear choosers (seven females and five males) that initiated divorce by moving to a new birds site or by courting a new partner at their current site. Choosers improved their reproductive success after the divorce, whereas their previous partners, the victims did not. Yearly divorce rates (average 8.2% per year) were significantly correlated with yearly mortality rates. Divorces appear to be opportunistic: pairs divorced after varying numbers of reproductive failures with the immediate precursor usually being the disappearance (death) of a murre from a successful neighboring site. In contrast to the delays experienced by victims, choosers formed new pairs quickly and laid their eggs no later than reuniting pairs. Prior to the divorce, victims fed their chicks less often than choosers, and some engaged in other behaviors that compromised egg or chick survival. These observations suggest that deficiencies in parental behavior were precursors to the divorce. This report is one of the first cases where reproductive failure of divorcing pairs has been linked to deficits in the parental behavior of the subsequent divorce victim.Communicated by C. Brown     

Site fidelity and patterns of short- and long-term movement in the brilliant-thighed poison frog <Emphasis Type="Italic">Allobates femoralis</Emphasis> (Aromobatidae)

We studied movement and site fidelity of males and females of the territorial frog Allobates femoralis (Aromobatidae) in a population in the Nature Reserve “Les Nouragues” in French Guiana, South America. Observations during 3 months in 2006 ascertained intra-seasonal site fidelity for males and females. Males actively defend large multi-purpose territories whereas females retreat to small resting sites from where they commute to neighbouring males for courtship and mating. Female short-term movement corroborates the previous assumption of a polygynous or promiscuous resource-defence mating system. Year-to-year recaptures from 2005 until 2008 revealed distinct patterns of inter-annual movement for males and regional site fidelity for females. Males abandon their territories and have to re-negotiate them when reproduction starts again at the end of the dry season. Females are not subject to intra- or inter-sexual territorial competition and as a result move significantly less between reproductive seasons than males. Male long-term movement reflects spatial structure and prevailing social interactions and is a reliable indicator for tadpole deposition sites. The combined effects of intra- and inter-seasonal movement promote the diversity of mates for both sexes.     

Do female zebrafish withhold reproductive resources for future mating opportunities?

Because polyandry often confers substantial direct and indirect benefits, females might be advantaged if they limit their reproductive investment in a single male when additional partners are available. We tested whether females of the externally fertilizing zebrafish Danio rerio would withhold more of their clutch when immediate further matings were likely. We tested females in three treatments: overnight visual and olfactory exposure to either a single male, two males, or three males. Females were then allowed to mate with one of the males; in the two-male and three-male treatments, the additional males remained in visual and olfactory contact to simulate a high likelihood of additional mating. Available clutch was measured by leaving females to spawn with two novel males for an additional 60?min. In contrast to our expectations, females did not release a greater proportion of their clutch when only a single male was present. Instead, females in the single male treatment released significantly fewer eggs per spawning event and significantly fewer eggs over the full 70?min of the trial. The hypothesis that females adjust current reproductive investment support in relation to the likely availability of mating partners is not supported. Instead, females appear to lay fewer eggs when only one male is available, most likely as a result of physiological stimulation of oocyte maturation, or in response to the likely fertilization capacity of a single individual.     

Rank-related partner choice in the fission–fusion society of the spotted hyena (<Emphasis Type="Italic">Crocuta crocuta</Emphasis>)

When social partners vary in their relative value, individuals should theoretically initiate partnerships with conspecifics of the highest value. Here, we tested this prediction in a wild population of spotted hyenas (Crocuta crocuta). Crocuta live in complex, fission–fusion societies structured by dominance hierarchies in which individuals vary greatly in their value as social companions. Because patterns of association among Crocuta reflect social preferences, we calculated association indices (AIs) to examine how social rank influences intrasexual partner choice among unrelated adults of both sexes. The highest-ranking individuals were generally most gregarious in both sexes. Females associated most often with dominant and adjacent-ranking females. Females joined subgroups based on the presence of particular conspecifics such that subordinates joined focal females at higher rates than did dominants. Dominants benefit from associations with subordinates by enjoying priority of access to resources obtained and defended by multiple group members, but the benefits of these associations to subordinates are unknown. To investigate this, we tested three hypotheses suggesting how subordinates might benefit from rank-related partner choice among unrelated females. We found that subordinates who initiated group formation benefited by gaining social and feeding tolerance from dominants. However, rates at which dominants provided coalitionary support to subordinates did not vary with AIs. Overall, our data resemble those documenting patterns of association among cercopithecine primates. We consider our results in light of optimal reproductive skew theory, Seyfarth’s rank attractiveness model, and biological market theory. Our data are more consistent with the predictions of Seyfarth’s model and of biological market theory than with those of skew theory.     

Males in the shade: habitat use and sexual segregation in the Galápagos sea lion (Zalophus californianus wollebaeki)

In many sexually dimorphic species adult sexes tend to segregate socially, spatially, or in habitat use. Several hypotheses have been formulated regarding underlying mechanisms. We investigated terrestrial habitat use and sexual segregation in a tropical otariid, the Galápagos sea lion (Zalophus californianus wollebaeki), where most of the hypotheses can be ruled out a priori. Factors relating to thermoregulation and costs of locomotion were of prime importance for habitat use. Habitats directly adjacent to the sea, with simple structured flat surfaces, shade, and tide pools were most frequented, but sexes and age classes differed in their usage patterns. Sexual segregation, both spatial and by habitat was pronounced in the reproductive period (RP), but remained high during the nonreproductive period (NRP). A GLM model of habitat use showed that in both seasons adult males frequented habitat types that adult females and other age classes used much less. Males were most abundant in suboptimal inland habitats, which offered only shade for cooling. Females with newborns differed in habitat use from females with older offspring and lone females. Spatial and habitat segregation are explained most parsimoniously as by-products of social processes, primarily intrasexual competition and female avoidance of male harassment, linked to the polygynous mating system.Electronic Supplementary Material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Philopatry,reproductive success of females,and maternal investment in the red-necked wallaby

Summary Female red-necked wallabies settle within their mothers' home ranges, apparently for life, while males disperse at about two years of age. However, sons spend much more time with their mothers before dispersing than do daughters of similar ages. Females who associate regularly with their subadult offspring are less likely to reproduce successfully at their next breeding attempt than are females who spend little time with their subadults, and sons therefore impose greater short-term reproductive costs on their mothers than do daughters. Females who are generally gregarious also suffer reduced reproductive success, even though reproductive success is independent of local density. It is suggested that the reproductive costs to females of associating with their subadult offspring, and other relatives, are incurred through tolerance of ecological competition from those kin, and therefore reflect a form of prolonged maternal investment, which is initially heaviest in sons but is sustained for longer periods in daughters. Females produce equal numbers of male and female offspring, and spend equal amounts of time suckling them in infancy.     

Fallow deer polyandry is related to fertilization insurance

Polyandry is widespread, but its adaptive significance is not fully understood. The hypotheses used to explain its persistence have rarely been tested in the wild and particularly for large, long-lived mammals. We investigated polyandry in fallow deer, using female mating and reproduction data gathered over 10 years. Females of this species produce a single offspring (monotocous) and can live to 23 years old. Overall, polyandry was evident in 12 % of females and the long-term, consistent proportion of polyandrous females observed, suggests that monandry and polyandry represent alternative mating strategies. Females were more likely to be polyandrous when their first mate had previously achieved high numbers of matings during the rut or was relatively old. However, polyandry was not related to the following factors: female age, the stage of the rut, the dominance ranks of mates, or the number of daily matings achieved by males. Polyandrous and monandrous multiple-mating females were not more likely than single-mating females to be observed with an offspring during the following year, and there were no significant differences in offspring size between these females. These results provide support for a fertility insurance hypothesis, with females remating if fertilization from the first mating was uncertain due to possible sperm depletion. The potential for different female mating strategies among large, polygynous mammals has generally been overlooked. Our findings highlight the complexity of female reproductive strategies and the possible trade-offs between fertilization success, preferences for high-quality males, and potential costs of polyandry, particularly for monotocous species.     

Testosterone and the allocation of reproductive effort in male house finches (Carpodacus mexicanus)

Testosterone has been proposed to serve as the mediator that controls the relative effort that an individual male bird will devote to mating effort versus parental effort. Here, we demonstrate a testosterone-influenced trade-off between parental and mating efforts in male house finches. Male house finches with experimentally elevated testosterone fed nestlings at a significantly lower rate, but sang at a higher rate than males without manipulated testosterone levels. Females mated to testosterone-implanted males fed nestlings at a significantly higher rate than females mated to males without testosterone implants, resulting in similar feeding rates for both treated and untreated pairs. The effects of testosterone on male house finches, however, were not as dramatic as the effects of testosterone observed in some other socially monogamous species of birds. Because extra-pair copulations are uncommon in house finches and males provide substantial amounts of parental care, these more modest effects may be due to differences in how the allocation of reproductive effort affects the costs and benefits of different reproductive behaviors. Received: 6 June 2000 / Accepted: 17 July 2000     

Strategic use of allopreening in family-living wrens

A prominent interaction in the lives of social mammals is allogrooming. Individuals allogroom strategically and preferentially, grooming high-quality individuals that control access to resources. This results in distinct patterns of allogrooming within social groups, such that some individuals are groomed more than the others, some dyads express symmetry in allogrooming, and others exchange allogrooming for other benefits. Allopreening, the avian equivalent of allogrooming, occurs commonly in group-living birds, providing the opportunity to test whether social birds also use allopreening strategically in their social relationships. I examined this hypothesis in family-living buff-breasted wrens (Cantorchilus leucotis) by examining allopreening initiation, reciprocation and rate during interactions involving breeding adults and offspring. Buff-breasted wrens exhibit a nuclear family structure in which pairs display long-term partnerships, and juveniles delay dispersing from natal territories for about 10 months. Allopreening was symmetrical between breeding partners: males and females who initiated and reciprocated allopreening of partners with similar frequency, and within reciprocated bouts, allopreening was time-matched. Pairs in which allopreening was not observed were more likely to divorce, but allopreening patterns did not change in successive years of partnerships. Parent–offspring allopreening, by contrast, was asymmetrical in pattern; parents initiated allopreening more than their offspring, and reciprocation never occurred. The different patterns of allopreening observed within buff-breasted wren families suggest the strategic use of allopreening, possibly for the maintenance of long-term partnerships and in exchange for social benefits from offspring.     

Polyandry, multiple mating, and female fitness in a water strider Aquarius paludum

Contrary to Bateman’s principle, polyandry appears to be a common female mating strategy. Several hypotheses have been proposed to explain the evolution of polyandry. It is assumed that females gain either material or genetic benefits from multiple matings, or that they are coerced into mating by males. In water striders, mating is generally assumed to be costly to females, and they are thought to mate for reasons of convenience, adjusting their resistance to mating according to male harassment. Here, we tested the effect of number of matings (with the same male) and number of partners on female fitness in a water strider Aquarius paludum. In the first experiment, we regulated the time females spent with a male and found that females’ egg production increased with multiple matings up to a point. The result supports the existence of an optimal female mating frequency. In the second experiment, we tested how polyandry affects the number of eggs laid and egg hatching success. We conducted three different trials: females mated four times with either a single male, two different males, or with four different males. Females that mated with four different males laid the lowest number of eggs and had the lowest egg hatching success, suggesting that polyandry reduces females’ egg production and egg hatching success in A. paludum. We conclude that A. paludum females probably gain material benefits from mating but no genetic benefits were found in this study.     

Loss of mating opportunities influences refuge use in the Iberian rock lizard,<Emphasis Type="Italic"> Lacerta monticola</Emphasis>

Because time spent in refuge may be costly if prey lose opportunities to forage, fight, or mate, prey allow predators to approach closer before beginning to flee when opportunity costs are high. Because the same opportunity costs may apply to refuge use as to escape, prey should make similar trade-offs between risk of emerging and cost of remaining in refuge. In the Iberian rock lizard, Lacerta monticola, we studied the effects of sex, reproductive season, speed of predator approach, and potential loss of mating opportunities on time spent in refuge following simulated predatory attacks. Lizards of both sexes adjusted refuge use to the level of risk by spending more time in refuge when approached rapidly than slowly. Females remained in refuge for equal times in the mating and postreproductive seasons, but males emerged sooner during the mating season, suggesting adjustment to a cost of lost opportunity to search for mates during the mating season. When a tethered female was nearby, males emerged from refuge earlier than if no female was present, indicating a trade-off between risk and mating opportunity. Approach speed affected emergence time when females were absent, but not when a female was present. Approach speed did not affect the probability that, after emerging, a male would return to court the female. For males that courted females intensely (bit them) before entering refuge, approach speed did not affect latency to emerge, but males that courted less intensely emerged sooner if approached slowly than rapidly. These findings show that males adjust the length of time spent in refuge to both risk of predation and reproductive cost of refuge use.Communicated by A. Mathis     

Evolution of extreme-mating behaviour: patterns of extrapair paternity in a species with forced extrapair copulation

Sexual conflict can result in the evolution of extreme mating strategies, including forced copulation. Forced extrapair copulation (FEPC) is generally rare among birds, but is common in re-introduced populations of the hihi (Notiomystis cincta), a socially monogamous, New Zealand endemic, endangered passerine. The aim of this study was to understand the patterns of extrapair paternity in a population where the majority of EPC is forced and to examine the factors, in particular female-specific, influencing the proportion of offspring fathered by extrapair males (EPP—extrapair paternity) and the number of males siring extrapair offspring within a brood (EPM) in this species. Using 8 years of comprehensive paternity, life-history and demographic information for 485 breeding attempts, we show that the frequency of EPP is dependent on (1) social male and female age, (2) the month the female fledged, (3) breeding density and (4) whether it was their first or second reproductive event of the season. In addition, we show that both EPP and EPM are negatively associated with breeding synchrony and clutch size is the most important predictor of EPM. Understanding the drivers of EPP and EPM in species with FECP is important because these are strong determinants of variance in reproductive success and the maintenance of extreme mating behaviour.     

High rates of extra-pair young in the pair-living fat-tailed dwarf lemur, Cheirogaleus medius

Cheirogaleids are one of the most primitive extant primate taxa in the world. Their lifestyle and mating system, therefore, have been considered to be representative for social systems in primate ancestors. Accepted models of social evolution in primates state that pair-bonding has evolved secondarily from diurnal group-living taxa and should therefore be constrained primarily to diurnal species. In contrast to these assumptions, the nocturnal fat-tailed dwarf lemur (Cheirogaleus medius) lives in permanent pairs, with obligate paternal care probably representing the evolutionary basis of pair-living. In this sociobiological field study, we analyzed the reproduction strategy of C. medius in the tropical forest of western Madagascar. In the rainy seasons from 1995 to 1999, 173 individuals of C. medius were captured and individually marked and 131 were genetically characterized through seven microsatellite loci. Additionally, 36 of these individuals were radio-tracked and observed. For 53 genotyped individuals, including 16 offspring, information about pair-bonding and family structure was known from field observations. Genetic analyses revealed that yearlings and infants living with an adult pair were in all cases sibs of the social mother. However, C. medius does not restrain from extra-pair copulations (EPCs) and a high rate of extra-pair paternity (44%) was detected. Males sired offspring with their female partners as well as with extra-pair females within the same year, indicating that males may increase their reproductive success by EPCs without necessarily running the risk of cuckoldry. Females on the other hand do not seem to run the risk of reduced paternal care, either because males cannot detect relatedness of young, or because they might even increase their inclusive fitness by raising offspring of closely related males. Since females reproduce preferentially with territory holders and no paternity could be assigned to floating males, superior genetic quality of the males might be crucial for female choice. Received: 12 January 2000 / Revised: 15 August 2000 / Accepted: 26 August 2000     

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.