Low frequency of extra-pair fertilisations in House Sparrows breeding at high density

The importance that the density of breeders has on the opportunity for extra-pair fertilisations (EPFs) is controversial. Some evidence supports the idea that population density and frequency of extra-pair paternity are positively associated, whereas other work does not. In the present paper we estimate EPF frequency in a dense House Sparrow Passer domesticus colony. We detected extra-pair nestlings in 9.3% of 54 broods studied, and 7% of 171 nestlings were sired by extra-pair fathers. The number of clutches laid per female, the change of male or female between two consecutive breeding attempts and the age of the partners showed no association with the presence or absence of extra-pair fertilisations. Morphometric variables of paired males and females did not discriminate broods with EPFs from those without. We detected a single case of a female laying a "parasitic" egg in the nest of a male that in a previous breeding attempt was the extra-pair genetic father of her entire brood. The frequency of extra-pair fertilisation recorded in this study was low compared with that in other House Sparrow populations breeding at lower densities, or other species that breed in colonies. This result does not support the claim that EPF frequency is associated with population density. We propose, as an explanation for this result, that under high intra-sexual competition for nest sites (1) males may have limited opportunities to search for females for extra-pair copulations and (2) the high quality of male nest-owners may reduce female propensity to search for additional sexual partners.     

Experimental manipulation of timing of breeding suggests laying order instead of breeding synchrony affects extra-pair paternity in house sparrows

The timing of breeding may not only affect breeding patterns such as the overlap of chick rearing period with the peak in food availability but also the opportunity for extra-pair mating. A negative relationship has been predicted between extra-pair paternity and breeding synchrony, assuming that male extra-pair activity is traded against mate guarding and parenting duties. In contrast, if female ability to assess male quality is temporally constrained, sperm competition might be a positive function of breeding synchrony. Here we manipulated the progress of nesting by nest material exchange within nesting aggregations to see whether the timing of breeding affects extra-pair paternity in house sparrows. We found that late broods within nesting clusters contained extra-pair young more often than early broods, but breeding synchrony did not turn out to be a significant predictor of extra-pair paternity. Our study indicates that temporal constraints of male extra-pair activity may account for extra-pair paternity levels, but it is also possible that late-breeding females may accept extra-pair copulations to ensure egg fertilization.     

An alternative route to coloniality in the bearded tit: females pursue extra-pair fertilizations

We combine behavioral studies with DNA-fingerprinting of a populationof bearded tits Panurus biarmicus and test the idea that thepursuit of extra-pair copulations by females acts as selectivepressure that may contribute to the formation of colonies inthis socially monogamous species. We show that the rate of extra-pairpaternity in colonial breeding pairs is very high, whereas noextra-pair chicks were detected in solitary nests. We foundno cases of extra-pair maternity and intraspecific brood parasitismin solitary nests, whereas it did occur in dense breeding situations.We further found no difference in the quality of males betweencolonial and solitary individuals. However, colonial femaleswere of significantly higher quality in terms of body size andcondition. We propose that high-quality females settle in coloniesto increase their opportunities to adjust the choice of theirsocial partner by obtaining extra-pair copulations. We suggestthat colony formation enables high-quality females to incitemale-male competition for extra-pair copulations and consequentlysecure extra-pair fertilizations by high-quality males and thathigh-density nesting is controlled by female bearded tits     

Paternal care declines with increased opportunity for extra-pair matings in fairy martins

Following the discovery that extra-pair fertilizations are common in many birds, it has been predicted that male participation in parental care may be influenced by their opportunity for extra-pair copulations. However, such a trade-off between male contribution to parental care and the availability of fertile females has not been confirmed. Here we use a novel remote monitoring technique to show that participation in incubation by male fairy martins, Hirundo ariel, declines with the increasing availability of fertile females in the breeding colonies. Furthermore, male contribution to incubation is most responsive to change in the availability of fertile females in the early morning, when most copulations occur, and also if their clutches are smaller than average. Both of these patterns support the presence of a trade-off between parental and extra-pair copulation effort. We suggest that this trade-off may be widespread among the 90% of bird species where males contribute to parental care.     

Low incidence of extra-pair paternity in the colonially nesting common swift Apus apus

The frequency of extra-pair paternity in a wild colony of swifts Apus apus was determined by multilocus DNA fingerprinting in two successive breeding seasons. The data were used to examine the expectation that extra-pair paternity is frequent in colonial-nesting species, either for proximal reasons such as the increased opportunity for extra-pair matings, or because extra-pair matings are important in the evolution and maintenance of coloniality. Forty-two broods containing 88 chicks were analysed. The genetic analysis revealed four cases of extra-pair paternity (4.5% of chicks) from four (9.5%) nests. Rapid mate-switching was considered unlikely to be the cause of extra-pair paternity since three of the cases were in the nests of previously established breeding pairs. Extra-pair copulations were not observed, but were assumed to be the cause of extra-pair paternity. The data show that high levels of extra-pair paternity are not an inevitable feature of high-density nesting.     

Male rank, female breeding synchrony, and patterns of paternity in the boat-tailed grackle

Species in which males directly defend groups of breeding femalesoften have extreme skew in observed male mating success. Inonly a few species, however, has a corresponding skew in fertilizationsuccess been confirmed. Furthermore, the ecological and socialfactors contributing to variation in fertilization success needinvestigation. This study examined competition for mates andpaternity in the boat-tailed grackle (Quiscalus major). Observationsat colonies of nesting females revealed that the toprankingor alpha males performed more than 70% of the copulations. DNAfingerprinting indicated that alpha males sired less than 40%of nestlings. Nevertheless, analysis of band-sharing scoresamong nestlings from different nests suggested that alpha malessired more than three times as many offspring as any other individualmale. Because few nestlings were sired by the nonalpha malesthat associated with colonies, females must have mated withother males while on trips away from colonies. Analysis of paternitywithin broods revealed that at least half of all females hadtheir brood fertilized by more than one male. Alpha males' successat fertilizing eggs did not vary with the number of simultaneouslyreceptive females within a colony. Our results suggest that maleand female behavior in female-defense polygyny results fromcomplex coevolution of the sexes.     

Intrusion into neighboring home range by male Madagascar paradise flycatchers, Terpsiphone mutata: a circumstantial evidence for extra-pair copulation

The seasonal change in home range size and distribution of the male Madagascar paradise flycatcher, Terpsiphone mutata, was studied in deciduous dry forest of the Ampijoroa Forest Station, northwestern Madagascar. Male home ranges were spaced out in the prebreeding period but overlapped during the breeding period; this change resulted from male intrusion into neighboring home ranges. Male intrusion was often observed during the prelaying and laying stages of females in invaded home ranges. These stages are assumed to be in a fertile period of females. Intruder males tended to have longer tails as compared to resident males. Intruder males may be seeking extra-pair copulations. Females may prefer long-tailed males to short-tailed males as extra-pair partners, or long-tailed males may be dominant to short-tailed males. Received: February 17, 2000 / Accepted: April 25, 2000     

Can redistribution of breeding colonies on a landscape mitigate changing predation danger?

The reproductive success of colonially breeding species depends in part upon a trade‐off between the benefit of a dilution effect against nestling predation within larger colonies and colony conspicuousness. However, there may be no net survivorship benefit of dilution if smaller colonies are sufficiently inconspicuous. This raises the question about how the size distribution of breeding colonies on a landscape might change as the predation danger for nestlings changes. In southwest British Columbia, Canada, bald eagle Haliaeetus leucocephalus populations have increased exponentially at ～5% per year in recent decades and prey upon nestlings of colonial breeding great blue herons Ardea herodias faninni. Motivated by field data on reproductive success in relation to colony size, modeling is used to ask under which circumstances trading off a dilution benefit against colony conspicuousness can improve population reproductive success. That is, which colonial nesting distribution, dispersed and cryptic versus clumped and conspicuous, best mitigates predation danger on nestlings? When predators are territorial, the modeling predicts a dispersed nesting strategy as attack rate increases, but not as predator numbers increase. When predators are non‐territorial, the modeling predicts a dispersed nesting strategy as predator numbers and/or attack rates increase. When predators are both territorial and non‐territorial, colonial nesting within a predator's territory improves reproductive success when attack rates are low. This suggests nesting in association with territorial predators may offer decreased levels of predation when compared with nesting amongst non‐territorial predators. Thus a change in the colony size distribution of colonially breeding species might be anticipated on a landscape experiencing a change in predation danger.     

Sexual selection in the monogamous barn swallow (Hirundo rustica). II. Mechanisms of sexual selection

Mechanisms of sexual selection in the monogamous, sexually dimorphic barn swallow (Hirundo rustica) were studied during a seven-year period. First, the sex ratio of reproducing adults was male-biased, and mated males had significantly longer tail ornaments than unmated males. Secondly, some of the unmated individuals later committed infanticide and became mated with the mother of the killed brood. Fathers of killed broods had significantly shorter tails than other males, and there was a tendency for infanticidal males to have longer tail ornaments than other unmated males. Thirdly, long-tailed male barn swallows were more successful in acquiring extra-pair copulations than other males, and females involved in extra-pair copulations, as compared to females not involved in such copulations, had mates with shorter tail ornaments. Fourthly, male barn swallows having long tails as compared to short-tailed males acquired mates in better body condition. Females mated to long-tailed males reproduced earlier, laid more eggs and were more likely to have two clutches than were females mated to short-tailed males. Finally, females mated to long-tailed males put more effort into reproduction than did other females, as evidenced by their relatively larger contribution to feeding of offspring. Thus, at least five different components of sexual selection affected male reproductive success. Selection arising from differential success during extra-pair copulations, differential reproductive success and differential male reproductive effort thus accounted for most of the selection on tail ornaments in male barn swallows.     

Sperm Competition and Copulation Intervals of the White Spoonbill (Platalea leucorodia,Aves, Threskiornithidae)

Some aspects of sperm competition were studied in the white spoonbill (Platalea leucorodia) breeding in Doñana National Park (SW Spain). Shorter pair copulation intervals occurred during the prelaying period, when females were subjected to a relatively high frequency of extra-pair copulations. Pair copulation intervals with an intermediate extra-pair copulation by the male mate were longer than those without extra-pair copulation. This result indicates that males need a time of recovery between copulations before they can perform another. Extra-pair copulations by the females did not affect the length of intervals between pair copulations. There were no differences between the lengths of the intervals between an extra-pair copulation by the female and the following pair copulation for cases in which the male mate detected an intruder male attempting copulation with his mate and those in which the intruder remained undetected. However, the correlations obtained between copulatory intervals for detected and undetected cases suggest a copulatory response by their mates, although affected by the required recovery time between copulations by the males. Finally, since extra-pair copulations mainly occurred while male mates were collecting nest material, they engaged in this activity shortly after pair copulations, probably to avoid a last-male advantage under the sperm competition pressure.     

High occurrence of extra-pair partnerships and homosexuality in a captive Cape Vulture Gyps coprotheres colony§

The Cape Vulture Gyps coprotheres is an Endangered colonial cliff-nesting species that is typically cited as monogamous. Observations of wild Cape Vulture colonies note extra-pair breeding activities but homosexual activity has never been confirmed. Observations of breeding behaviours within a captive colony were conducted at VulPro’s breeding facilities in South Africa The captive breeding programme included 10 breeding pairs and a total of 41 non-releasable, individually recognisable, and genetically sexed subadults or adults. Observations were conducted over the 2014 breeding season as part of a study investigating the social and rearing conditions of chicks intended for release in a population supplementation programme. A high percentage of total colony copulation attempts (22%) were extra-pair copulations but only 23 interactions resulted in cloacal contact or possible sperm transfer. Four paired males formed extra-pair relationships, two of which were homosexual.     

The effect of breeding density and male quality on paternity-assurance behaviours in the house sparrow, <Emphasis Type="Italic">Passer domesticus</Emphasis>

Several factors can influence the risk of cuckoldry through extra-pair paternity for male birds. The number of neighbouring males is thought to affect the chance of females engaging in extra-pair copulations, and species which breed both socially (colonially) and solitarily provide an ideal opportunity to test the effect of close proximity on extra-pair behaviour and paternity guards. In this study, the extent to which male house sparrows, Passer domesticus, used two alternative strategies, namely frequent copulation and mate-guarding, to ensure paternity was investigated. We also examined how males vary the two paternity guards according to their breeding sociality. Pairs at the dense colony started to copulate at a higher rate at the beginning of the fertile period than those of the medium-sized colony and solitary breeding pairs. Male house sparrows appear to fine-tune their strategies according to the breeding density. Both strategies are alternatively used in the weak fertile period but are simultaneously used in the peak fertile period. Our results suggest that males modify their strategy according to their individual abilities: mate-guarding intensity was positively correlated with the black breast badge size.     

Corvids congregate to breeding colonies of a burrow‐nesting seabird

Egg predation is a major cause of reproductive failure among birds, and can compromise the viability of affected populations. Some egg predators aggregate near colonially breeding birds to exploit the seasonal increase of prey resources. We investigated spatial and temporal variations in the abundance of an egg predator (little raven Corvus mellori; Corvidae) to identify whether ravens aggregate spatially or temporally to coincide with any of three potential prey species: burrow‐nesting little penguin (Eudyptula minor; Spheniscidae), short‐tailed shearwater (Ardenna tenuirostris; Procellariidae), and surface‐nesting silver gull (Chroicocephalus novaehollandiae; Laridae). We derived spatially explicit density estimates of little ravens using distance sampling along line transects throughout a calendar year, which encompassed little penguin, short‐tailed shearwater and silver gull breeding and non‐breeding seasons. High raven abundance coincided temporally with penguin and gull egg laying periods but not with that of shearwaters. The spatial distribution of raven density corresponded with the little penguin colony but not with shearwater or gull colonies. Thus, the presence of little penguin eggs in burrows correlated strongly with little raven activity, and this implies that little ravens may have learnt to exploit the plentiful subsurface food resource of little penguin eggs. Corvid management may be required to maintain the viability of this socially and economically important penguin colony.     

Reproductive Synchrony and Extra-pair Copulation in Birds

We present a model which explores the idea that females may reduce their risk of suffering a forced extra-pair copulation, by breeding synchronously with other females in the population. Information from three bird species with contrasting ecology and behaviour shows that synchrony does not automatically confer an advantage on females: synchrony is only advantageous to females if certain conditions pertain. We identify three main factors which influence female extra-pair copulation risk, these are: (i) whether or not males can identify fertile females, (ii) male and female ‘availability’ (e.g. in some seabirds copulation and extra-pair copulations occur only at the colony: females may be absent for long periods and hence are unavailable for extra-pair copulations), (iii) the timing of extra-pair copulations by males, relative to when their partners lay.     

Space,density and extra-pair matings have opposing impacts on male and female reproductive success

Many territorial species have a mating system characterized by males establishing home ranges in the breeding grounds prior to females, resulting in males competing for territories and females choosing a mate upon their arrival. It remains unknown, however, how the outcomes of decisions surrounding territory establishment and mate choice are influenced by the spatial configuration of the breeding grounds. We use a spatially explicit, individual-based model to investigate the sex-specific effects of these decisions on reproductive success. In our model, males that arrive earlier obtain higher quality territories and improve their chances for extra-pair copulations. Females can choose their mate to maximize the quality of the male or to attempt to minimize the density of other females near their nesting site to avoid competition. Females therefore face a tradeoff between high-density regions around high-quality males and low-quality males in areas of low competition. Our model predicts a negative correlation between male and female reproductive success under a wide range of conditions when the majority of the territories are on the margins of the breeding area. Most notably, this sexual conflict arises as an edge effect suggesting that fragmentation of breeding habitats could impact the consequences of mate choice in many species with territorial breeding habits.     

The distribution of extra-pair young within and among broods – a technique to calculate deviations from randomness

Molecular paternity tests show that extra-pair fertilizations are common in many socially monogamous bird species. However, the question of why females often seek extra-pair copulations is still controversial. Competing alternative explanations differ in their predictions on how extra-pair young should be distributed within and among broods. Analysing these distributions may therefore help to resolve this controversy. In several species broods without extra-pair young and those with total or nearly total extra-pair paternity have been claimed to be over-represented. Consequently, extra-pair nestlings would be distributed non-randomly among nests. To compute expected frequencies (i.e. the patterns of random distribution) the Poisson distribution has frequently been used. However, the Poisson distribution is not appropriate for two reasons. (1) Impossible configurations can receive positive probabilities. (2) The Poisson distribution approaches randomness only if extra-pair fertilizations are events of low probability, which often is not the case. We show how randomness can be computed appropriately by using the multivariate hypergeometric distribution. Re-analysing published data on distributions of extra-pair young, we show that the result that there are more broods containing either none or many extra-pair young than expected by chance is even more pronounced than previously thought.     

Experimentally reduced male attractiveness increases parental care in the pied flycatcher Ficedula hypoleuca

This study reports effects of experimental manipulations ofreproductive effort and the size of the male's white foreheadpatch (a secondary sexual trait), on provisioning rates, reproductivesuccess, and parental breeding dispersal distance in the piedflycatcher, Ficedula hypoleuca. Parents caring for enlargedbroods resulting from manipulated clutches provisioned nestsat higher rates than parents with reduced broods. Males with a reduced forehead patch fed their nestlings more in relationto males with an unmanipulated forehead patch, and their youngfledging with a longer tarsi. This suggests that males witha reduced attractiveness may perceive their own attractivenessand they devote more time available for parental effort given their poorer prospects in male contest competition and/or femaleattraction for extra-pair copulations. However, their femalesdid not alter their provisioning effort and this runs counterto both the differential allocation and the partner-compensationhypotheses. An artificial decrease in a male secondary sexualtrait led to a wider breeding dispersal distance between successiveyears.     

Male song sparrows Melospiza melodia do not announce their female's fertility

We tested the fertility announcement hypothesis, whereby male song during a female's fertile period functions as both a paternity guard and an advertisement for extra-pair copulations, in an eastern population of song sparrows Melospiza melodia over two broods within a breeding season. Our results did not support one of its main predictions: male song rate was not significantly higher in the female's fertile period than in her post-fertile period. Song rate peaked prior to pairing, when males were establishing territories and trying to attract females. Once paired, song rate dropped by a factor of about ten, and was consistently low through all stages of the nesting cycle. Males who failed to pair continued singing at high rates throughout the breeding season. Our results do not support the fertility announcement hypothesis, therefore song rate is not used primarily as a paternity assurance strategy by song sparrows.     

The influence of rainfall and nest-site quality on the population dynamics of the Manx shearwater Puffinus puffinus on Rhum

The Manx shearwater colony in the mountains of Rhum receives a high average rainfall, around 3000 mm, and nest burrows are subject to flooding. Colony hatching success rates on Rhum and neighbouring Canna are significantly negatively correlated with rainfall amounts during the incubation period. The incidence of heavy rainfall during incubation has a greater influence on hatching success than does total rainfall. Fledging success is unrelated to rainfall. Burrows vary with respect to their susceptibility to flooding during heavy rain. A 'Flooding Likelihood Index'(FLI) was devised which allowed 100 study burrows to be ranked with respect to their risk of flooding in a given rainfall event. Eggs were significantly more likely to be laid and to hatch in burrows less susceptible to flooding. In 1984 and 1985 the overall breeding success rate in burrows with an FLI lower than the median was more than twice that in those with higher than median FLIs. Male shearwaters showed a significantly greater tendency to move to different burrows following breeding failure in the previous season. This may be an adaptive response to the consistent differences in the quality of individual burrows. The shearwater population on Rhum may be limited by the availability of good quality nesting burrows.     

Does competition for nests affect genetic monogamy in Cory's shearwater Calonectris diomedea?

Most bird species are socially monogamous. However, extra‐pair copulations (EPCs), resulting in extra‐pair paternity (EPP), commonly occur. EPCs should allow females to adjust social mate choice and allow males that fail to obtain a nest a chance to avoid missing a breeding season, especially when poor nest supply constrains social mate choice. Procellariiformes (albatrosses and petrels) are socially monogamous seabirds which seldom divorce, even when nest availability constrains social mate choice. In Cory's shearwater Calonectris diomedea, a burrow‐nesting petrel, two studies conducted in the Mediterranean, where competition for nests is weak, detected no EPP. EPP remains to be investigated at localities where competition for nests is much stronger, such as Vila islet, Azores archipelago, Atlantic Ocean. We conducted a genetic (microsatellites) study over two successive years on Vila, involving the breeding pairs of the same 65 nests each year and their single chick. EPPs occurred each year, the overall rate being 11.6%. Coupling genetic analyses to a 7‐year demographic survey provided additional data on pair bonds and competition for nests. Overall, cuckoldry was unrelated to divorce, nest density and inbreeding avoidance, but was more frequent when the social male was small. Nest changes were more costly for males than for females, and some apparently unpaired males attempted to dislodge social males during within‐pair copulations. These results are compatible with the existence of a link between poor nest availability and EPP and confirm that even species considered strongly monogamous can adopt flexible mating strategies.