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.     

Copulatory behaviour in the colonial Eurasian Griffon vulture Gyps fulvus

We examined copulation patterns and associated sexual behaviour in the colonial Eurasian Griffon vulture Gyps fulvus during the pre-laying period. Eurasian Griffon vulture pairs conducted an average of 71.7 copulation attempts per clutch, with an average copulation frequency of 1.2 copulation attempts per day. Low copulation frequencies compared to other raptors and absence of mate-guarding suggest that this species does not possess adaptive behaviour aimed at increasing paternity assurance. However, the gradual increase in copulations during the fertile period is consistent with the sperm competition hypothesis.     

Paternity Loss in Relation to Male Age, Territorial Behaviour and Stress in the Pied Flycatcher

For sexual selection to operate in monogamous species, males of poor quality in some factor like age, ornamentation, condition or aggressiveness, should lose paternity compared with higher quality males. We tested this idea in an Iberian population of pied flycatchers ( Ficedula hypoleuca ). Microsatellite analysis of 67 broods revealed moderate levels of extra-pair paternity (22.4% of broods, 7.5% of young). In a sample of 58 broods for which the caring male was identified, a higher paternity loss was associated with younger males, males that were less aggressive during territorial intrusion tests performed before the commencement of laying, and with males that showed higher levels of corticosterone metabolites in faecal samples collected at the end of the nestling period. Plumage darkness, forehead patch size and condition were not related to paternity loss. Paternity loss is more related to behavioural or physiological traits than to morphological ones in this population.     

Factors influencing mate guarding and territory defence in the stitchbird (hihi)

Socially monogamous male birds are predicted to maximise their reproductive success by pursuing extra-pair copulations (EPCs) while engaging in anti-cuckoldry behaviour such as mate guarding. In the stitchbird, Notiomystis cincta, high levels of forced EPCs and a high proportion of nestlings resulting from extra- pair fertilisations lead to the prediction that males of this species should exhibit intense paternity guarding behaviours. While studying an isolated stitchbird population on Tiritiri Matangi Island New Zealand (3636'S, 17453'E), I collected daily behavioural data throughout the breeding season from 15 males in 2000/01 and 27 males in 2001/02. In this study, male stitchbirds demonstrated clear paternity guarding by exhibiting: (1) an increased likelihood of being close to their mate during her fertile period, (2) an increased initiation of mate contact during her fertile period, (3) switching from site-specific territorial defence during the pre-fertile period to defending an area centring on the their female partners location during her fertile period, and (4) an increased following of the female to communal feeding sites outside the territory during her fertile period. For polygynous males, mate guarding and territorial defence were conditional on which of their females was fertile. Additional evidence supporting the hypothesis that mate guarding in this species is a form of paternity assurance, rather than protection from harassment, is that males protected their partner from harassment by other stitchbird males but did not intervene when females were harassed by male bellbirds, Anthornis melanura. While mate-guarding intensity in many species is conditional on the stage of female fertility, male stitchbirds also modified their behaviour depending on the location of the female and the rate of intrusions by extra-pair males. Resident males adopted a best-of-a-bad-job tactic when they were unable to locate their female by defending an area around her last known location. Furthermore, when the rate of intrusions by extra-pair males increased they traded-off the area they could defend within their territory against their ability to guard the female. Territory takeovers were uncommon, but when they did occur older males displaced younger males and healthy birds displaced sick ones. Contrary to the prevailing view that mate guarding is a male response to female infidelity, male stitchbirds appear to use mate guarding primarily to prevent paternity losses from forced EPCs. Future assessments of mate guarding function should consider the possibility that mate guarding involves a combination of conflict and co-operation between the sexes.     

Females discriminate against heterospecific sperm in a natural hybrid zone

When hybridization is maladaptive, species‐specific mate preferences are selectively favored, but low mate availability may constrain species‐assortative pairing. Females paired to heterospecifics may then benefit by copulating with multiple males and subsequently favoring sperm of conspecifics. Whether such mechanisms for biasing paternity toward conspecifics act as important reproductive barriers in socially monogamous vertebrate species remains to be determined. We use a combination of long‐term breeding records from a natural hybrid zone between collared and pied flycatchers (Ficedula albicollis and F. hypoleuca), and an in vitro experiment comparing conspecific and heterospecific sperm performance in female reproductive tract fluid, to evaluate the potential significance of female cryptic choice. We show that the females most at risk of hybridizing (pied flycatchers) frequently copulate with multiple males and are able to inhibit heterospecific sperm performance. The negative effect on heterospecific sperm performance was strongest in pied flycatcher females that were most likely to have been previously exposed to collared flycatcher sperm. We thus demonstrate that a reproductive barrier acts after copulation but before fertilization in a socially monogamous vertebrate. While the evolutionary history of this barrier is unknown, our results imply that there is opportunity for it to be accentuated via a reinforcement‐like process.     

Reproductive character displacement of female,but not male song discrimination in an avian hybrid zone

Divergence of male sexual signals and female preferences for those signals often maintains reproductive boundaries between closely related, co‐occurring species. However, contrasting sources of selection, such as interspecific competition, can lead to weak divergence or even convergence of sexual signals in sympatry. When signals converge, assortative mating can be maintained if the mating preferences of females diverge in sympatry (reproductive character displacement; RCD), but there are few explicit examples. Pied flycatchers (Ficedula hypoleuca) are sympatric with collared flycatchers (F. albicollis) on the Baltic island of Öland, where males from both species compete over nestboxes, their songs converge, and the two species occasionally hybridize. We compare song discrimination of male and female pied flycatchers on Öland and in an allopatric population on the Swedish mainland. Using field choice trials, we show that male pied flycatchers respond similarly to the songs of both species in sympatry and allopatry, while female pied flycatchers express stronger discrimination against heterospecific songs in sympatry than in allopatry. These results are consistent with RCD of song discrimination of female pied flycatchers where they co‐occur with collared flycatchers, which should maintain species assortative mating despite convergence of male sexual signals.     

Do Male Pied Flycatchers (Ficedula hypoleuca) Adjust Their Feeding Effort According to Egg Colour?

The colour of blue‐green bird eggs has been hypothesized to signal female quality to attending males, who may adjust their level of investment in the brood accordingly. The hypothesis has gained support in studies of Spanish pied flycatchers Ficedula hypoleuca. We performed a cross‐fostering experiment in a Norwegian population of pied flycatchers to provide an independent test of the sexually selected egg colour hypothesis in this species. Egg colour was not significantly correlated with estimates of female quality (clutch size, average egg volume, first egg laying date and feeding rate). There was a significant decrease in chroma and increase in brightness and egg volume during the laying sequence, with some marked differences between six‐egg and seven‐egg clutches that might reflect differences in female quality. However, we found no significant influence of egg colour (foster or original clutch) on male feeding rate or offspring viability (hatching success, average mass and fledging success) and no significant difference in feeding rate for males with six‐egg and seven‐egg foster or original clutches. We conclude that Norwegian male pied flycatchers do not use egg colour as a cue to female quality, thus questioning the generality of previous support for the sexually selected egg colour hypothesis from this species.     

Mate guarding in the Seychelles warbler is energetically costly and adjusted to paternity risk

Males may increase their fitness through extra-pair copulations (copulations outside the pair bond) that result in extra-pair fertilizations, but also risk lost paternity when they leave their own mate unguarded. The fitness costs of cuckoldry for Seychelles warblers (Acrocephalus sechellensis) are considerable because warblers have a single-egg clutch and, given the short breeding season, no time for a successful replacement clutch. Neighbouring males are the primary threat to a male's genetic paternity. Males minimize their loss of paternity by guarding their mates to prevent them from having extra-pair copulations during their fertile period. Here, I provide experimental evidence that mate-guarding behaviour is energetically costly and that the expression of this trade-off is adjusted to paternity risk (local male density). Free-living males that were induced to reduce mate guarding spent significantly more time foraging and gained significantly better body condition than control males. The larger the reduction in mate guarding, the more pronounced was the increase in foraging and body condition (accounting for food availability). An experimental increase in paternity risk resulted in an increase in mate-guarding intensity and a decrease in foraging and body condition, and vice versa. This is examined using both cross-sectional and longitudinal data. This study on the Seychelles warbler offers experimental evidence that mate guarding is energetically costly and adjusted to paternity risk.     

POPULATION DIVERGENCE IN SEXUAL ORNAMENTS: THE WHITE FOREHEAD PATCH OF NORWEGIAN PIED FLYCATCHERS IS SMALL AND UNSEXY

Models of sexual selection suggest that populations may easily diverge in male secondary sexual characters. Studies of a Spanish population of the pied flycatcher, Ficedula hypoleuca, and a Swedish population of the closely related collared flycatcher, F. albicollis, have indicated that the white forehead patch of males is a sexually selected trait. We studied the white forehead patch of male pied flycatchers (n = 487) in a Norwegian population over seven years. Males with large forehead patches were in general more brightly colored, but patch height was not correlated to body mass, body size, or parasite loads. Conditions during the nestling period did not seem to influence patch height as an adult. Patch height increased slightly from the first to the second year as adults, but then remained relatively constant at higher ages. Patch height was not related to survival. Year-to-year changes showed that males who increased in patch height also increased in body mass, suggesting that expression of the forehead patch may be partly condition dependent. However, changes in body mass explained only a small proportion of the variance in patch height between males. Thus, patch height would not be a good indicator of male quality. Furthermore, patch size was also not related to male ability to feed nestlings, indicating that females would not obtain direct benefits by choosing males with large patches. However, patch height could be a Fisher trait, but this requires heritability and there was no significant father-son resemblance in patch height. Comparisons of the males visited by each female during the mate sampling period indicated that chosen males did not have larger forehead patches than rejected males. Experimental manipulation of patch height did not affect male mating success. These results indicate that females do not use patch size as a mate choice cue. Finally, patch height did not predict the outcome of male contests for nestboxes, suggesting that the forehead patch is not an intrasexually selected cue of status. Norwegian pied flycatchers have smaller forehead patches than both Spanish pied flycatchers and Swedish collared flycatchers. We suggest that this pattern may be explained by the lack of sexual selection on the forehead patch in the Norwegian population as compared to the other populations, where the patch is apparently sexually selected. We discuss possible reasons for these population divergences, such as female choice on an alternative secondary sexual character (general plumage color) and speciation among Ficedula flycatchers.     

Extra-pair paternity in the shag, Phalacrocorax aristotelis as determined by DNA fingerprinting

The frequency of chicks resulting from extra-pair copulation in the shag, Phalacrocorax aristotelis , was measured by DNA fingerprinting. DNA fingerprints were taken from both sexes of 15 pairs and their chicks (28) in a subcolony on the Isle of May, UK. It was found that 18% of the chicks had extra-pair paternity, and one chick (3.5%) was not the offspring of either member of the pair, implying either a polygynous male whose second female was fertilized by another male or adoption. Although no observations of courtship and copulation were made in the same season, observations in a previous year on the same colony of shags showed that 14.1% of the copulations by males were not with the female with whom that male reared young. The similarities and differences are discussed between these results on the level of extra-pair copulations and of extra-pair paternity and those of other studies where both observations of extra-pair copulations and various measures of the degree of extra-pair paternity have been made.     

Malaria infections reinforce competitive asymmetry between two Ficedula flycatchers in a recent contact zone

Parasites may influence the outcome of interspecific competition between closely related host species through lower parasite virulence in the host with which they share the longer evolutionary history. We tested this idea by comparing the prevalence of avian malaria (Haemosporidia) lineages and their association with survival in pied and collared flycatchers (Ficedula hypoleuca and F. albicollis) breeding in a recent contact zone on the Swedish island of Öland. A nested PCR protocol amplifying haemosporidian fragments of mtDNA was used to screen the presence of malaria lineages in 1048 blood samples collected during 6 years. Competitively inferior pied flycatchers had a higher prevalence of blood parasites, including the lineages that were shared between the two flycatcher species. Multistate mark–recapture models revealed a lower survival of infected versus uninfected female pied flycatchers, while no such effects were detected in male pied flycatchers or in collared flycatchers of either sex. Our results show that a comparatively new host, the collared flycatcher, appears to be less susceptible to a local northern European malarial lineage where the collared flycatchers have recently expanded their distribution. Pied flycatchers experience strong reproductive interference from collared flycatchers, and the additional impact of species‐specific blood parasite effects adds to this competitive exclusion. These results support the idea that parasites can strongly influence the outcome of interspecific competition between closely related host species, but that the invading species need not necessarily be more susceptible to local parasites.     

The role of genetic constraints and social environment in explaining female extra-pair mating

Why do females of socially monogamous species engage in extra-pair copulations? This long-standing question remains a puzzle, because the benefits of female promiscuous behavior often do not seem to outweigh the costs. Genetic constraint models offer an answer by proposing that female promiscuity emerges through selection favoring alleles that are either beneficial for male reproductive success (intersexual pleiotropy hypothesis) or beneficial for female fecundity (intrasexual pleiotropy hypothesis). A previous quantitative genetic study on captive zebra finches, Taeniopygia guttata, reported support for the first, but not for the second hypothesis. Here, we re-examine both hypotheses based on data from lines selected for high and low male courtship rate. In contrast to previous conclusions, our new analyses clearly reject the hypothesis that male and female promiscuity are genetically homologous traits. We find some support for a positive genetic correlation between female promiscuity and fecundity. This study also shows that the behavioral outcome of extra-pair courtships primarily depends on individual-specific female preferences and not on the “attractiveness” of the social mate. In contrast, patterns of paternity are strongly influenced by the social partner and the pair bond, presumably reflecting variation in copulation behavior, fertility, or sperm competitiveness.     

Experimentally Simulating Paternity Uncertainty: Immediate and Long-Term Responses of Male and Female Reed Warblers Acrocephalus scirpaceus

In many socially monogamous species, both sexes seek copulation outside the pair bond in order to increase their reproductive success. In response, males adopt counter-strategies to combat the risk of losing paternity. However, no study so far has tried to experimentally prove the function of behaviour for paternity assurance. Introducing a potential extra-pair partner during the female fertile period provides a standardised method to examine how pair members respond immediately (e.g. increase mate guarding or copulation frequency) or long term (e.g. later parental investment and paternity uncertainty). In this study on a socially monogamous passerine species, we experimentally confronted pairs of reed warblers with a conspecific male (caged male simulating an intruder) during egg-laying. Our results revealed that occurrence of an intruder during that period triggered aggression against the intruder, depending on the presence of the female. The male territory owner also attacked the female partner to drive her away from the intruder. Thus territory defence in reed warblers also serves to protect paternity. The increase in paternity uncertainty did not affect later paternal investment. Paternal investment was also independent of the actual paternity losses. In females, the experiment elicited both, immediate and long-term responses. E.g. female copulation solicitations during the intruder experiment were only observed for females which later turned out to have extra-pair chicks in their nest. In relation to long term response females faced with an intruder invested later less in offspring feeding, and had less extra-pair chicks in their nests. Extra-pair paternity also seems to be affected by female quality (body size). In conclusion female reed warblers seem to seek extra-pair fertilizations but we could demonstrate that males adopt paternity assurance tactics which seems to efficiently help them to reduce paternity uncertainty.     

Female lesser kestrel ( falco naumanni ) also accepts extra-pair copulation

The lesser kestrel (Falco naumanni) is considered a socially monogamous species in which extra-pair copulation occurs at a low rate. A wide study of extra-pair mating behaviour carried out on this species found that mated females do not solicit extra-pair copulation and reject all copulation attempts elicited by extra-pair males. In fact, the infrequent instances of extra-pair fertilization found were attributed either to re-mating after divorce, or polygyny. Here I describe an observation indicating that females also promote and accept promiscuous mating, attaining and consummating extra-pair copulation. I suggest the possibility that promiscuous behaviour could vary among different populations in this species, as it has not yet been reported, in spite of the extensive work performed in this respect.     

Sequential mating patterns suggest extra-pair mating is not part of a mixed reproductive strategy by female red-winged blackbirds

Studies aimed at determining why female birds often produce offspring sired by males other than their social mates generally compare traits of social and genetic mates. Here I examine paternity patterns in nests of the same female red-winged blackbirds (Agelaius phoeniceus) in successive breeding seasons. Returning females preferentially selected their former social mates as their new social mates when those males were present. However, paternity patterns were much less consistent. A female''s behaviour (faithful versus unfaithful) in one year did not predict her behaviour the following year. Females unfaithful in successive years did not prefer the same extra-pair males. Females unfaithful in one year that switched social mates the next year did not preferentially choose their former extra-pair mates as their new social mates. By switching genetic mates, females did not generally improve the quality of their mates. These results, together with previous analyses, suggest that female blackbirds in this population have little control over extra-pair mating. Although females may benefit from extra-pair mating because extra-pair males are generally longer lived, paternity patterns in this population are not consistent with extra-pair mating being part of a finely tuned female reproductive strategy.     

Yearling male great tits, Parus major, suffer more strongly from cuckoldry than older males

In the majority of socially monogamous bird species, females have offspring sired by males other than their social mate as the result of extra-pair copulations. While it is widely recognised that there is considerable variation in the frequency of extra-pair paternity between species, between populations of a species and between individuals of a population, determinants of this variation are surprisingly difficult to establish. With respect to individual variation within a population, it is an important step to test for male and female correlates of cuckoldry to better understand the patterns as well as the adaptive significance of extra-pair mating behaviour. Here, we analysed patterns of extra-pair paternity in relation to male age, female age and their interaction in the great tit Parus major, a socially monogamous passerine with a moderate frequency of extra-pair paternity. Based on a large sample of 316 genotyped first broods from five successive years, we failed to demonstrate interaction effects of male and female age on both the proportion of extra-pair offspring and the likelihood that at least one extra-pair offspring is present within a brood. However, both the proportion of extra-pair offspring and the likelihood of paternity loss were higher for yearling as compared to older males, while this was not the case for yearling vs. older females. Furthermore, the proportion of extra-pair offspring within a brood decreased with increasing age of the attending male in within-individual analyses. We found a comparable effect also for attending females in within-individual analyses, but only when excluding two individuals with 100% extra-pair paternity. A female (extra-pair) mating preference for older males and/or a limited ability of yearling males to prevent cuckoldry in their broods could explain these age-related patterns of paternity loss. Effect sizes, however, were not particularly large and substantial residual variation within age categories suggests the importance of further yet unidentified determinants of variation in paternity loss in the study population.     

Song similarity predicts hybridization in flycatchers

Given that population divergence in sexual signals is an important prerequisite for reproductive isolation, a key prediction is that cases of signal convergence should lead to hybridization. However, empirical studies that quantitatively demonstrate links between phenotypic characters of individuals and their likelihood to hybridize are rare. Here we show that song convergence between sympatric pied (Ficedula hypoleuca) and collared flycatchers (F. albicollis) influence social and sexual interactions between the two species. In sympatry, the majority of male pied flycatchers (65%) include various parts of collared flycatcher song in their song repertoire (but not vice versa). Playback experiments on male interactions demonstrate that male collared flycatchers respond similarly to this 'mixed' song as to conspecific song. Long-term data on pairing patterns show that males singing a converged song attract females of the other species: female collared flycatchers only pair with male pied flycatchers if the males sing the mixed song type. From the perspective of a male pied flycatcher, singing a mixed song type is associated with 30% likelihood of hybridization. This result, combined with our estimates of the frequency of mixed singers, accurately predicts the observed occurrence of hybridization among male pied flycatchers in our study populations (20.45% of 484 pairs; predicted 19.5%). Our results support the suggestion that song functions as the most important prezygotic isolation mechanism in many birds.     

Copulation behaviour and paternity in shy albatrosses (Thalassarche cauta)

We investigated the mating system of shy albatrosses Thalassarche cauta by combining behavioural observations during the pre-laying period with genetic paternity analysis. Genetic data on the mating systems of several procellariiform seabirds have recently become available, but data on the reproductive behaviour of these species are rarely obtained. Our main aims were to describe the copulatory behaviour of this species and identify how males achieve within-pair and extra-pair paternity (EPP). Most copulations occurred on the nest, were unforced and were within-pair. Females controlled the success of copulations and were observed soliciting extra-pair matings. Within-pair and extra-pair copulations were behaviourally similar. A low frequency (7–10%, n =29 chicks) of EPP was detected despite male use of frequent copulation as a paternity guard. The pre-laying foraging exodus of female shy albatrosses differed from that in other albatrosses: it was relatively short in length, lasting c . 2 days, and within-pair copulations occurred after the female's return 2 days before laying. This may reflect the close proximity of feeding grounds to the breeding colony.     

Sex‐Specific Associations Between Nest Defence,Exploration and Breathing Rate in Breeding Pied Flycatchers

Correlations between behavioural traits constrain animals to a limited range of behavioural choices and set a limit to the available variation in behavioural phenotype of a population. These constraints are especially important during stressful situations, potentially limiting the ability to cope with stress appropriately. As yet, very little consideration has been given to a possible role for sexual selection in maintaining differences in behavioural stability within individuals: sex‐specific differences in behavioural correlations have been seldom studied, especially in the wild. In this field study, we investigated associations between neophobia (latency to enter nest in the presence of a novel object), nest defence (response to a model predator) and breathing rate in response to handling in breeding pied flycatchers (Ficedula hypoleuca). We did not find any significant difference in antipredator responses between males and females, which indicates low sexual conflict over parental care in the pied flycatcher. However, females were more neophobic than males, while males and females did not differ in their breathing rates. Further, our study demonstrated a strong positive correlation between nest defence behaviour and neophobia in male, but not in female pied flycatchers. Males that defended their nest more had lower breathing rate and higher latency to resume nestling feeding after encountering a predator decoy than males that mobbed less intensely. We found only weak evidence that nest partners might affect each other's behaviour in these contexts.     

The effects of male mating behaviour and food provisioning on breeding success in snow buntings <Emphasis Type="Italic">Plectrophenax nivalis</Emphasis> in the high Arctic

For passerine birds breeding in the Arctic, paternal effort in parental care is necessary for successful breeding. Behavioural strategies, such as mate guarding, to ensure paternity should therefore also be common in this environment. In order to investigate the relation between such behaviour and breeding success, when controlling for the effect of environmental factors, we recorded male mate-guarding behaviour, parental effort and breeding success amongst snow buntings, Plectrophenax nivalis, in the high Arctic environment of Spitsbergen, Svalbard. Mate-guarding intensity tended to positively affect male feeding frequency per nestling in one of the study years, negatively in 1 year and without effect in the 3rd year. The negative effect in 1999 was strong, but variation in estimates of the 2 other years was high and the effect of mate guarding may be negligible in these 2 years. We assume that this pattern might be related to yearly variation in the prevalence of extra-pair young. Male food provisioning was not positively related to breeding success, but late breeders had higher breeding success than early breeders. Thus, the effect of male mate guarding is highly variable and mainly affects food provisioning rates, but the benefit for total breeding success seems to be marginal, at best.