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.     

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.     

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.     

Lack of Mate-guarding in a Territorial Passerine Bird with a Low Intensity of Sperm Competition,the Pied Flycatcher; (Ficedula hypoleuca)

We examined a Norwegian population of pied flycatchers (Ficedula hypoleuca) for behaviour associated with the paternity-protection tactic of mate-guarding and found that this tactic was absent. The absence of mate-guarding and the fact that pied flycatchers do not have a high rate of copulation make this population unusual to the extent that the current literature implies that, in birds, one or other paternity guard should be present. Comparison of our population with a Swedish population that does exhibit mate-guarding lends some support to the notion that differences in nesting density may drive the relative risk of extra-pair copulation, leading to the need for paternity guards such as mate-guarding. However, we conclude that, whilst the results of both our study and the Swedish study are consistent with the nesting-density hypothesis, there is at least one other plausible hypothesis that fits the available data. Specifically, we direct attention to the role of the female in determining overall patterns of pair behaviour and, potentially, the rate of extra-pair paternity, challenging the primacy of male—male competition as the driving force behind the sperm-competition dynamics of this species.     

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.     

Variation in Song Rate during the Breeding Cycle of the Chaffinch,Fringilla coelebs

The variation in song rate during the breeding season was studied in two individually marked chaffinch Fringilla coelebs populations. We gathered data to investigate especially the recently presented mate-guarding hypothesis. The active singing has been supposed to function as a form of mate guarding during the female's fertile period by announcing the high status of the male and preventing extra-pair copulations by neighbouring males. There was no clear dawn chorus in the chaffinch, i.e. a peak in the song rate before sunrise. Male chaffinches continued to sing after mating, but the song rate dropped significantly. In contrast to the mate-guarding hypothesis the song rate was lower during the fertile period of the female than during pre-mating and incubation. Thus, the males do not announce the fertility status of their mates or their own quality and status by active singing. The song does not function as a form of mate guarding in the chaffinch. One function of the song of the chaffinch is mate attraction: singing activity was highest before pair formation in early spring and decreased after mating but increased again if the male lost his mate later in the breeding season.     

Do male paternity guards ensure female fidelity in a duetting fairy-wren?

Most socially monogamous bird species engage in extra-pair mating,and consequently males may adopt various behavioral strategiesto guard paternity. However, the relationship between mate guardingand extra-pair paternity is unclear: low levels of extra-pairpaternity can be associated either with no mate guarding orwith intense mate guarding. We investigate paternity guardsin the purple-crowned fairy-wren (Malurus coronatus), a duettingspecies where extra-pair paternity is rare. This species isunusual in a genus known for extremely high levels of extra-pairmating. We examine the behavioral interactions between the sexesunderlying these low rates of extra-pair paternity and showthat male purple-crowned fairy-wrens do not use frequent copulationor courtship feeding to assure paternity or guard females acousticallyby duetting. Males maintain close proximity to females bothwhen they are fertile and when they are not breeding and donot invest in courtship displays to extra-pair females. Consistentwith predictions of theoretical models, low extra-pair paternityin this species may be related to female fidelity rather thanmale paternity assurance strategies, but short-term removalof males would be necessary to test this experimentally.     

No evidence of genetic benefits from extra-pair fertilisations in female sand martins (Riparia riparia)

Genetic parentage studies of socially monogamous birds reveal a widespread prevalence of extra-pair paternity. Variation in extra-pair paternity among individuals may depend on how different individuals benefit from extra-pair fertilisations and on the opportunity to pursue extra-pair copulations. A long-term study of sand martins (Riparia riparia) in Hungary allowed us to examine patterns of extra-pair fertilisations in a large colony of over 3,000 breeding pairs with many known age individuals. We used multi-locus DNA fingerprinting to determine whether extra-pair fertilisations occur when females are paired to (1) presumably low quality mates, or (2) genetically similar or dissimilar mates, and whether extra-pair fertilisations result in offspring of higher quality. Extra-paternal young were found in 38% of 47 broods and comprised 19% of 190 offspring. Males that lost paternity did not differ significantly from others in age or body condition. Social mates of broods containing extra-pair offspring did not differ in genetic similarity from pairs without extra-pair offspring. Furthermore, there was no significant difference in body condition between extra-pair young and their maternal half-siblings. We were unable to assign paternity and therefore cannot exclude the possibility that extra-pair males differed from the within-pair males they cuckolded, in age, body condition or genetic similarity with the female. We found a positive relationship between paternity losses and breeding density, suggesting that low breeding density may constrain opportunities for seeking extra-pair copulations.     

Extra-pair paternity in relation to regional and local climate in an Arctic-breeding passerine

Reproductive processes are affected by local and regional climate variation. Birds breeding in the Arctic may experience strong energetic constraints, which will affect their reproductive output. Recent research has emphasized the importance of extra-pair copulation as a means of improving reproductive output. In this paper, we explore ecological and climatic determinants that may explain variation in extra-pair paternity (EPP) in an arctic-breeding passerine, the snow bunting Plectrophenax nivalis. EPP occurred in 10.8 % of the young and 20.9 % of the broods sampled from 1999 to 2003. We found that the proportion of extra-pair young in a nest was positively related to the body size and age of the social male and weakly negatively related to the local average minimum temperature prior to the onset of egg laying. These results suggest that older and larger males lost a larger share of paternity than smaller and younger males, and that the relative loss of paternity decreased with cold weather during the female’s fertile period. Large and old males spend less time mate guarding compared to small and young males and may allocate more time towards extra-pair forays, and thus lose more paternity in their own nest. Climatic conditions most likely constrain the total energy budget with less energy available for extra-pair activity in cold weather.     

Population density and the intensity of paternity assurance behaviour in a monogamous wader: the Curlew Numenius arquata

We compared paternity assurance behaviour and related displays in high (1.6 pairs perkm²) and low (6.7 pairs per km²) density populations of the Curlew Numenius arquata breeding on arable farmland in western Finland. There was little evidence of individuals pursuing extra-pair copulations or males exhibiting paternity assurance behaviour. Furthermore, there was no variation in the frequency of intrusions or in the intensity of paternity assurance behaviour relative to lay date. However, intrusions and approaches to the pair female by extra-pair males were more frequent at high breeding density, and pair males remained closer to their female, followed her more and exhibited a higher frequency of copulatory behaviours in the high-density population. Therefore, high breeding density appeared to increase opportunities for individuals to copulate outside the pair-bond and resulted in more intense male paternity guards. Male song flight displays were also more frequent in the high-density population. Territorial absences by males were infrequent in both areas. The increased frequency of intrusions and interactions between non-pair individuals (male-male and male-female) at high density were probably the major factors in explaining area differences in the intensity of paternity assurance and territorial behaviour.     

Fitness consequences of hybridization between house sparrows (Passer domesticus) and tree sparrows (P. montanus)

Gene transfer may occur following hybridization between closely related species if hybrids are viable and able to breed with individuals of one or both of the parental species. House (Passer domesticus) and tree sparrows (P. montanus) occasionally hybridize and produce viable offspring. Previously, we concluded that male tree × house sparrow hybrids are most probably fertile based on the observation of a male F1 hybrid feeding the nestlings with a female house sparrow in two consecutive clutches. However, recent DNA analyses based on blood samples revealed that all nestlings (4) in the first clutch were sired by a neighbouring house sparrow male, whereas nestlings in the second clutch (2) were not blood sampled and most probably died before fledging. This indicates that extensive extra-pair fertilization confounded our previous conclusion, and indicates that social partnership and attending behaviour can be imprecise measures of paternity.     

The mask of seniority? A neglected age indicator in house sparrows Passer domesticus

In many species, females prefer older males as social and genetic mates, and male secondary sexual traits often act as age indictor mechanisms. It has been reported that almost all the extra-pair paternity in one population and recently in another population of house sparrows Passer domesticus , was achieved by males more than one year old. We aimed to determine whether there is a morphological trait that distinguishes yearlings from older males in house sparrows. Here, we report that such a trait – the extent of black around a male's eye, which we term the 'mask' or 'mask of seniority', is a reasonable indicator of male age, being adequate to assign yearlings and older males correctly 81% of the time. It is well known that a male's black throat patch, often called the 'badge' or 'badge of status', signals fighting ability. We speculate that badge size signals dominance, and is therefore often used in male–male competition, whereas mask size may play a key role as an age indicator mechanism, potentially used in female choice. It is surprising that this important trait evaded researchers' attention during 20 years of house sparrows being a model organism for sexual selection.     

Intensity of nest defence is not related to degree of paternity in the willow tit Parus montanus

We asked whether willow tit Parus montanus males adjust their parental care according to their paternity in current brood. The origin of the nestlings was determined by using molecular technique, and the studied broods were assigned into extra-pair paternity (EPP) broods, if at least one nestling was fathered by another male, and truly monogamous broods. Over 3  years, 14 of 40  broods (35%) included EP-offspring, and 29 of 273  nestlings (11%) were EP-young. Intensity of parental care was measured with risk-taking against a potential predator, mounted stoat Mustela erminea . The results showed that risk-taking by EPP males did not differ from that by monogamous males. Neither was the sexual difference in risk-taking different at EPP and monogamous broods. Our results are consistent with the hypothesis that males do not adjust their level of care to paternity, perhaps because they have no reliable cues for assessing their paternity. This may be related to the success of mate-guarding in their breeding environment, closed forests. Guarding is seemingly successful as the EPP levels are rather low, but it is not totally sure making the potential costs, rejection of own young, too high. We also discuss other population characteristics which may further prevent the evolution of paternity assessment in northern willow tits.     

Breeding synchrony and extrapair paternity in a species with alternative reproductive strategies

Breeding synchrony may affect the tradeoff between pursuing multiple mates and avoiding paternity loss, translating into differences in the rate of extrapair paternity (EPP). However, diverse empirical relationships between breeding synchrony and EPP remain challenging to explain. We examined whether the relationship between breeding synchrony and EPP varied with male morph, age, body size, or breeding density in the white‐throated sparrow Zonotrichia albicollis. In this species, males of two genetically determined morphs pursue alternative mating strategies. Breeding synchrony positively correlated with EPP within polygamous white morph males, which have high rates of EPP and cuckoldry, but was unrelated to EPP within tan morph males, which prioritize mate guarding and paternal care. As previously reported, males that gained EPP were primarily white males. Males gained EPP more often than expected by chance during their mate's fertile period and on neighboring territories. Since extrapair copulation appears primarily male‐driven in this species, these results indicate that white males focus extra‐pair mating effort during periods of high synchrony and during their mates’ fertile periods, even at the expense of paternity loss within their own nests. Breeding density, male age, and male size did not modify the relationship between breeding synchrony and EPP. However, older white males had higher cuckoldry rates, perhaps reflecting declines in performance associated with senescence. Results suggest that, even within species, mating strategy may modify how breeding synchrony affects rates of EPP, with positive relationships manifest only within subsets of individuals that pursue a strategy of polygyny at the expense of paternity loss.     

Spatial and Temporal Distribution of Song in the Yellowhammer Emberiza citrinella

The temporal and spatial distribution of song was studied in a population of yellowhammers Emberiza citrinella. Song was most frequent during the breeding season, and within the breeding season during the fertile period of both first, second, and replacement clutches. Song activity peaked at sunrise and sunset. During the fertile period most singing took place in the central parts of the territory. Song post heights peaked during the fertile period, and more song posts lacked foliage at that time. Intrusions by male conspecifics peaked in the fertile period and in territories where males sang relatively little. Song activity and mate guarding were strongly positively correlated. Song volume was loud and song was thus apparently used in long-distance communication. These observations are in accordance with a male deterrence hypothesis, suggesting that males sing to deter neighbouring males from trespassing during the fertile period of their mate. A female attraction hypothesis, suggesting that males sing to attract neighbouring females and thereby obtain extra-pair copulations, and a female reproduction hypothesis, suggesting that males sing to start the female reproductive cycle, were partly supported by observations.     

Undirected Song Encourages the Breeding Female Zebra Finch to Remain in the Nest

Wild zebra finches sing frequently during the breeding season, but the vast majority of song is of the undirected song type that is not directed at any individual, and the function of which is obscure — it appears to be ignored by all potential recipients. It is sung close to the nest-site, has a peak in production during the egg-laying period, and diminishes thereafter. The incidence of undirected song is positively correlated with extra-pair courtship, a finding consistent with the hypothesis that it is a means of advertising availability for extra-pair matings. Typically, undirected song occurred outside the nest when the female was inside, and a positive relationship was found between the amount of singing given by the male during the 5-min interval immediately after the female entered the nest and the time she subsequently spent inside the nest. Keeping the partner inside the nest during her fertile period is an advantage to the male: it serves as a form of paternity protection against other males and it allows him opportunities to pursue his own extra-pair matings. Occupancy of the nest during laying is also a means of guarding against intraspecific brood parasitism, which was high at this colony.     

Territoriality as a paternity guard in the European robin, Erithacus rubecula

To investigate the relative importance of paternity defences in the European robin we used behavioural observations, simulated intrusions and temporary male removal experiments. Given that paired males did not increase their mate attendance, copulation rate or territory size during the female's fertile period, the most frequently quoted paternity assurance strategies in birds were absent. However, males with fertile females sang and patrolled their territories more regularly, suggesting that territorial motivation and vigilance were elevated when the risk of cuckoldry was greatest. In addition, there was a significant effect of breeding period on response to simulated intrusions: residents approached and attacked freeze-dried mounts more readily in the fertile period. During 90-min removals of the pair male in the fertile period, neighbours trespassed more frequently relative to prefertile and fertile period controls and appeared to seek copulations with unattended females. When replaced on their territories, males immediately increased both song rate and patrolling rate in comparison with controls. We propose that male robins sing to signal their presence, and increase their territorial vigilance and aggression in the fertile period to protect paternity. Copyright 2000 The Association for the Study of Animal Behaviour.     

Evidence from hatching success and DNA fingerprinting for the fertility of hybrid Pied × Collared Flycatchers Ficedula hypoleuca × albicollis

The Pied and Collared Flycatchers Ficedula hypoleuca and F. albicollis hybridize on the Baltic islands of Öland and Gotland. Field studies of hatching success in clutches from 36 breeding hybrid males indicate that male hybrids reproduce successfully. In comparison, 25 hybrid females had normal clutch sizes but failed to hatch nestlings, suggesting female hybrid sterility. The paternity of seven hybrid males was investigated by DNA fingerprinting using two hypervariable minisatellite probes. Of these hybrid males, six were assessed as fertile. Three of the hybrid male families (43%) contained nestlings with extra-pair paternity and the frequency of extra-pair fertilization among 37 nestlings was 22%. One nestling originated from intraspeciflc female nest parasitism. The sterility pattern in hybrids between these two flycatchers with sterile female and fertile male hybrids is in agreement with Haldane's rule.     

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.     

Multiple ornamentation, female breeding synchrony, and extra-pair mating success of golden whistlers (Pachycephala pectoralis)

Considerable variation exists in rates of extra-pair paternity between species, and across and within populations of the same species. Explanations for this variation include ecological (e.g. breeding synchrony), morphological (e.g. ornamentation), and genetic (e.g. relatedness) factors, but it is rare for studies to simultaneously explore these factors within a single population. This is especially true for highly ornamented species, where mate choice based on ornamentation may be more complex than in less-adorned species. We conducted such a study in a migratory population of the highly ornamented golden whistler (Pachycephala pectoralis). We quantified male genetic reproductive success and related it to a range of factors putatively involved in determining extra-pair mating success. We found no effects of genetic factors (male heterozygosity and relatedness) on extra-pair success, nor of territory size, male age, or incubation effort. Instead, males possessing yellower breast plumage and large song repertoires enjoyed higher reproductive success. Additionally, we found a negative relationship between local breeding synchrony and male extra-pair mating success. This may be a consequence of mate guarding during the female fertile period and an inability of males to simultaneously mate-guard and pursue extra-pair fertilisations. In this species, the opportunity for extra-pair matings appears to vary temporally with an ecological variable (local breeding synchrony), while fine-scale, inter-male differences in mating success may be influenced by individual attributes (male ornamentation). The migratory nature of the study population and its lack of natal philopatry may mean that relatedness and inbreeding avoidance are less important considerations in mate choice.