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Cooperative breeding behavior in birds ranges from inducible to obligate strategies and has evolved across diverse taxa, in species that display a wide range of social and reproductive behavior. It is often thought to evolve when independent breeding is constrained, and cooperation increases fitness. Yet many systems show variable, even maladaptive, fitness effects. This observation, together with the wide range in the form and frequency of cooperative breeding, raises the question of how the recurrent appearance of cooperative breeding and its extensive variation across species—from inducible to obligate—can be explained. Here, we take a proximate perspective on the evolution of cooperative breeding to argue that cooperative strategies are delineated by the history of prior adaptations and emerge through the rearrangement of preexisting neuroendocrine mechanisms underlying social, dispersal, and parental behaviors. Natural selection sorts among the resultant variants to alter regulation of cooperation, producing stabilization through either greater developmental entrenchment or greater reliance on environmental cues. Thus, species showing inducible cooperative behavior may be at a transitory stage in this process. To assess this possibility, we first evaluate evidence that the components of cooperative breeding are common across taxa. Then, we review the neuroendocrine mechanisms that regulate the pathways underlying cooperative strategies. Finally, we assess the evidence for neuroendocrine linkages during development that may channel coexpression of some components of cooperative breeding and facilitate its evolution. We conclude that understanding the mechanistic bases of the behaviors comprising cooperative breeding strategies may provide novel insight into the recurrent emergence of this strategy across disparate environments and avian taxa. [ABSTRACT FROM AUTHOR]

Joint nesting by females and cooperative polyandry—cooperatively breeding groups with a male-biased breeder sex ratio—are little-understood, rare breeding systems. We tested alternative hypotheses of factors potentially driving these phenomena in a population of joint-nesting acorn woodpeckers (Melanerpes formicivorus). During periods of high population density and thus low independent breeding opportunities, acorn woodpecker females formed joint-nesting coalitions with close kin. Coalitions were typically associated with groups with a male bias. We found strong evidence for both inter- and intrasexual conflict, as joint nesting conferred a fitness benefit to some males, a significant fitness cost to females, and no gain in per capita reproductive output for either sex. Such conflict, particularly the cost to females, may be an important reason why joint nesting is rare among cooperatively breeding taxa. [ABSTRACT FROM AUTHOR]

The article offers information on the radio tracking of mountain bluebirds visiting neighbors' nests. Topics include, North American bluebirds are secondary cavity nesters that readily accept nest boxes; documenting of cooperative breeding, prospecting for the future requires marked breeding pairs; and monitoring of mountain bluebirds by using RFID technology (Radio frequency identification systems).

Extra‐pair paternity (EPP) has been suggested to improve the genetic quality of offspring, but evidence has been equivocal. Benefits of EPP may be only available to specific individuals or under certain conditions. Red‐winged fairy‐wrens have extremely high levels of EPP, suggesting fitness benefits might be large and available to most individuals. Furthermore, extreme philopatry commonly leads to incestuous social pairings, so inbreeding avoidance may be an important selection pressure. Here, we quantified the fitness benefits of EPP under varying conditions and across life‐stages. Extra‐pair offspring (EPO) did not appear to have higher fitness than within‐pair offspring (WPO), neither in poor years nor in the absence of helpers‐at‐the‐nest. However, EPP was beneficial for closely related social pairs, because inbred WPO suffered an overall 75% reduction in fitness. Inbreeding depression was nonlinear and reduced nestling body condition, first year survival and reproductive success. Our comprehensive study indicates that EPP should be favored for the 17% of females paired incestuously, but cannot explain the widespread infidelity in this species. Furthermore, our finding that fitness benefits of EPP only become apparent for a small part of the population could potentially explain the apparent absence of fitness differences in population wide comparisons of EPO and WPO. [ABSTRACT FROM AUTHOR]

Natal dispersal is a demographic trait with profound evolutionary, ecological, and behavioral consequences. However, our understanding of the adaptive value of dispersal patterns is severely hampered by the difficulty of measuring the relative fitness consequences of alternative dispersal strategies in natural populations. This is especially true in social species, in which natal philopatry allows kin selection to operate, so direct and indirect components of inclusive fitness have to be considered when evaluating selection on dispersal. Here, we use lifetime reproductive success data from a long-term study of a cooperative breeder, the long-tailed tit Aegithalos caudatus, to quantify the direct and indirect components of inclusive fitness. We show that dispersal has a negative effect on the accrual of indirect fitness, and hence inclusive fitness, by males. In contrast, the inclusive, predominantly direct, fitness of females increases with dispersal distance. We conclude that the conflicting fitness consequences of dispersal in this species result in sexually antagonistic selection on this key demographic parameter. [ABSTRACT FROM AUTHOR]

Social interactions shape relationships between individuals in complex societies. Affiliative interactions are associated with benefits and strengthen social bonds, while aggressive interactions are costly and negatively affect social bonds. Individuals may attempt to reduce aggressive encounters through submissive displays directed at higher-ranking individuals. Thus, fine-scale patterns of affiliative, aggressive, and submissive interactions may reflect costly and beneficial social relationships within groups, providing insight into the benefits of group living and the mechanisms of conflict resolution. So far, however, most studies have looked at social interactions and benefits of group living in isolation. We investigated how the strength of social bonds (affiliative vs. aggressive interactions) and submissive displays varied with kin-selected and potential mating benefits, and with reproductive conflict in the cooperatively breeding purple-crowned fairy-wren, Malurus coronatus. Our results revealed that subordinates formed equally strong social bonds with kin and potential mates (unrelated opposite-sex individuals) while they formed antagonistic relationships with reproductive competitors that offered no kin-selected or mating benefits (unrelated same-sex individuals). Submissive displays were directed exclusively at same-sex breeders, regardless of relatedness. Affiliation and submission were associated with reduced foraging time when food was limited, indicating a cost to maintaining positive relationships. Together, our results suggest that the strength of social bonds is determined by (potential) benefits obtained from group members, while submission likely serves to reduce conflict. Our findings highlight the importance of time-costly social interactions for maintaining relationships with group members, providing insight into how social groups of individuals with (partly) divergent interests can remain stable. [ABSTRACT FROM AUTHOR]

Abstract: Dispersal is a key ecological process that influences the dynamics of spatially and socially structured populations and consists of three stages—emigration, transience, and settlement—and each stage is influenced by different social, individual, and environmental factors. Despite our appreciation of the complexity of the process, we lack a firm empirical understanding of the mechanisms underlying the different stages. Here, using data from 65 GPS‐collared dispersing female coalitions of the cooperatively breeding meerkat (Suricata suricatta), we present a comprehensive analysis of the effects of population density, mate availability, dispersing coalition size, and individual factors on each of the three stages of dispersal in a wild population. We expected a positive effect of density on dispersal due to increased kin competition at high densities. We further anticipated positive effects of mate availability, coalition size, and body condition on dispersal success. We observed increasing daily emigration and settlement probabilities at high population densities. In addition, we found that emigration and settlement probabilities also increased at low densities and were lowest at medium densities. Daily emigration and settlement probabilities increased with increasing female coalition size and in the presence of unrelated males. Furthermore, the time individuals spent in the transient stage increased with population density, whereas coalition size and presence of unrelated males decreased dispersal distance. The observed nonlinear relationship between dispersal and population density is likely due to limited benefits of cooperation at low population densities and increased kin competition at high densities. Our study provides empirical validation for the theoretical predictions that population density is an important factor driving the evolution of delayed dispersal and philopatry in cooperative breeders. [ABSTRACT FROM AUTHOR]

Nest predation has driven the evolution of specialized behaviors that decrease the probability that a predator encounters a nest. We collected descriptions from the literature of a behavior wherein male and female adults fly to their nest as a pair, with one bird flying onward or veering off while the other enters the nest. We suggest that the most likely function of this behavior is to decrease the risk of nest predation from visual nest predators. In this hypothesis, visual nest predators are distracted by the flying bird and thus fail to observe the bird arriving to the nest entrance (and the nest itself), although the putative adaptive value of this behavior remains to be confirmed. While this behavior has been sporadically noted in the natural history literature, few ornithologists are aware it is found across multiple taxa, especially in the Neotropics. We show that this behavior occurs in at least 28 species across 5 distinct families (and 11 genera) of passerines. We propose a classification scheme for this and similar behaviors and discuss factors hypothesized to promote the evolution of this behavior (e.g., mate guarding, building enclosed nests). We call this behavior "coordinated misdirection" (or "desvío coordinado" in Spanish) because it depends on the cooperation of at least 2 birds, and its presumed function is a visual misdirection—a ruse to draw the observers' attention away from the nest. Finally, we encourage future research so that the evolutionary history of the behavior can be explored and the behavior can be analyzed under a life history framework. [ABSTRACT FROM AUTHOR]

The genus Lanio is distributed from southern Mexico to northern Brazil. Until now, nesting information has been limited and scattered among Lanio species. Nests descriptions are available for 3 of the 4 species, and only L. versicolor has nestling descriptions. No information is available on incubation and feeding behavior or incubation and nestling periods for any Lanio species. We present detailed nesting biology information for L. versicolor, such as incubation and nestling behavior, eggs and nest thermal dynamics, and nestling feeding behavior, and also present the first evidence of cooperative breeding for the genus Lanio based on 11 nests monitored in the buffer zone of Manu National Park, Cusco, Peru. Nests were cup-shaped, and all had a leaf located above the nest. The clutch size was 2 eggs, white with maroon or wine-colored spots covering the shell surface. Incubation and nestling periods were 15 and 11 d, respectively, and daytime nest attentiveness was 78%. Nest architecture, clutch size, and nestling period were consistent with previous reports for the genus Lanio. We found similarities in the nesting biology of Lanio spp. with other species of the Tachyphoninae subfamily. Our study significantly increases the information available for the genus Lanio and provides novel and important information of cooperative breeding for a Neotropical mixed-species flock "leader" species. Yet, more studies are needed to fill the large information gap on nesting of tropical birds such as the species in the genus Lanio. [ABSTRACT FROM AUTHOR]

Research on cooperatively breeding birds usually focuses on social dynamics within the breeding group, but conflict between groups can also affect individual fitness and the evolution of sociality. Here we investigate the causes and consequences of competition between groups of communally breeding greater anis, Crotophaga major , over a 10-year field study. Social groups were spatially clustered into loose aggregations that showed a moderate degree of reproductive synchrony. However, competition between neighbouring groups for nesting sites was intense, occasionally leading to wholesale destruction of a group's nesting attempt and abandonment of the site. We documented 18 cases in which a group's entire clutch of eggs was ejected from the nest during the laying or incubation period, often accompanied by behavioural observations of conflict with a neighbouring group. Clutch destruction typically occurred when two groups attempted to nest in close proximity on high-quality sites: nearest-neighbour distance and nest site type were the strongest predictors of clutch destruction. Surprisingly, group size did not predict whether or not a group's clutch would be destroyed, and small groups sometimes ousted larger groups. By contrast, ‘home field advantage’ did have a significant effect: groups that had previously nested on the site were more likely to destroy the clutches of newly established groups, and this effect increased with the number of years that the group had nested there. Together, these results support previous evidence that competition between groups for high-quality nesting sites is an important driver of communal breeding, and they highlight the importance of location and past history in determining the outcome of intergroup contests in social species. Highlights • Cooperative groups of greater anis compete for nesting areas. • Groups may destroy entire clutches laid by neighbouring groups. • Length of tenure on the nest site, not group size, predicts competitive success. • Group stability and tenure affect competitive ability and individual fitness. [ABSTRACT FROM AUTHOR]

The evolution of helping behaviour in species that breed cooperatively in family groups is typically attributed to kin selection alone. However, in many species, helpers go on to inherit breeding positions in their natal groups, but the extent to which this contributes to selection for helping is unclear as the future reproductive success of helpers is often unknown. To quantify the role of future reproduction in the evolution of helping, we compared the helping effort of female and male retained offspring across cooperative birds. The kin selected benefits of helping are equivalent between female and male helpers--they are equally related to the younger siblings they help raise--but the future reproductive benefits of helping differ because of sex differences in the likelihood of breeding in the natal group. We found that the sex which is more likely to breed in its natal group invests more in helping, suggesting that in addition to kin selection, helping in family groups is shaped by future reproduction. [ABSTRACT FROM AUTHOR]

The eggshells of communally breeding greater anis Crotophaga major consist of a blue‐green pigmented calcite matrix overlaid by a chalky white layer of vaterite, both of which are polymorphs of calcium carbonate. The white vaterite layer is intact in freshly laid eggs and may function in protecting the eggs from mechanical damage, but it also abrades during incubation to reveal the blue calcite shell underneath. Previous research has shown that this color change serves a visual signaling function: nesting greater anis can discriminate between eggs that are freshly laid and those that have already been incubated, which allows them to reject asynchronous eggs laid by extra‐group parasites. Here we use avian visual modeling and pigment extraction to assess the perceptual and chemical bases of such egg recognition. We found that there was no overlap between the avian perceptual space occupied by ani eggshells with and without vaterite, and that vaterite lacked both of the pigments found in the eggshell's calcite matrix, bililverdin and protoporphyrin. The visual contrast between the unpigmented vaterite and the blue‐pigmented calcite appears to pre‐date the evolution of the signaling function, since the related guira cuckoo Guira guira, also a communal breeder, lays similarly structured and pigmented eggs but does not use the visual contrast as a signal to detect parasitism. [ABSTRACT FROM AUTHOR]

In many cooperatively breeding species, young ("helpers") from one year help other adults raise offspring the following year. In contrast to helper effects during the nestling or postfledging stages of the avian breeding cycle, potential benefits from helpers during incubation are poorly studied. We analyzed 39 clutches and recorded 6,027 offbouts to document incubation behavior in the White-breasted Thrasher (Ramphocinclus brachyurus), an endangered Neotropical facultative cooperative breeder. Our goal was to test the prediction that cooperation confers benefits during incubation in terms of increased nest attendance and hatching success. We found that 65% of active hours (0500-2100) are spent on the nest, values somewhat lower than average for a tropical passerine with uniparental incubation. Highest incubation constancy was observed at a rare 4-egg clutch, which was attended by putative jointnesters. Excluding this clutch, differences in incubation behavior between pair and cooperative groups were subtle and context dependent. We found temporal variation in incubation behavior, whereby off-bout frequency declined as the breeding season progressed, but more quickly for cooperative groups. Maximum ambient temperature was also an influential abiotic predictor. Across both social group types, incubation constancy declined as temperature increased to ~30°C, above which constancy remained high. As expected, we found that the behavior of birds with failed and successful clutches differed. Specifically, failed clutches experienced high early-season constancy, despite temperature data suggesting insufficient warming during that time, and successful cooperative clutches had higher late-season constancy than pairs. Other factors important in avian systems were not predictive of incubation behavior here, and in general, high individual variation for all incubation behaviors swamped most other sources of variation. Results from this work highlight the individuality in incubation behavior and suggest that breeding females in cooperative groups have more flexibility in shifting between incubation demands and maintenance behaviors than do lone pairs. [ABSTRACT FROM AUTHOR]

The Silvery-throated Jay ( Cyanolyca argentigula) is a poorly known Neotropical corvid endemic to the Cordillera de Talamanca of Costa Rica and western Panama. In April 2016, we found an active Silvery-throated Jay nest in Chirripó National Park, Costa Rica. Here we provide the first description of the breeding biology of this species, including nest architecture, estimates of incubation and nestling periods, and observations of adults attending the nest. The large cup nest, placement in the crown of a small tree, and breeding phenology are similar to other Cyanolyca species. We observed up to 5 adults associated with this nest, including at least 3 different adults that fed chicks. These observations suggest cooperative breeding at this nest but are also consistent with the possibility of communal breeding. Future studies with color-banded individuals and genetic sampling will be necessary to better understand what seems to be cooperative breeding in the Silvery-throated Jay. [ABSTRACT FROM AUTHOR]

Cooperative breeding, in which auxiliary group members help rear related, but nondescendent young, is often explained by kin selection. Reproductive monogamy is predicted in cooperatively breeding systems, as monogamy increases intragroup relatedness and maximizes auxiliary inclusive fitness. While monogamy is observed across many systems, including eusocial insects and cooperatively breeding mammals, some cooperatively breeding birds exhibit high rates of extrapair paternity. Here we quantify paternity and examine the role of auxiliaries on extrapair paternity in the highly cooperative variegated fairy-wren, Malurus lamberti , a species with both male and female auxiliaries. Extrapair paternity occurred in 55.4% of nests, and 39.8% of offspring were the result of extrapair matings. The presence of both male and female auxiliaries had a positive relationship with the percentage of within-pair young sired by dominant males, however, the presence of male auxiliaries had a stronger impact than the presence of females. The number of extrapair young sired by dominant males decreased as the number of male auxiliaries increased. The total number of young sired by dominant males, however, was not predicted by group size or relatedness to their social partner, nor did group composition or relatedness to the breeding pair predict the reproductive success of subordinate males. We hypothesize that breeders use alternative reproductive strategies in the presence or absence of auxiliaries. Males and females may seek extrapair reproductive opportunities when no help is available in their group and nest survival is expected to be low. When help is available, breeders may reduce extrapair paternity, either to increase intragroup relatedness or because confidence in nest survival is high. Our data suggest that group composition is important in understanding extrapair paternity rates in cooperatively breeding birds and that variation in extrapair paternity rates may be the result of flexible breeding strategies when auxiliary presence and identity varies. [ABSTRACT FROM AUTHOR]

How can altruism evolve or be maintained in a selfish world? Hamilton's rule shows that the former process will occur when rb > c--the benefits to the recipients of an altruistic act b, weighted by the relatedness between the social partners r, exceed the costs to the altruists c--drives altruistic genotypes spreading against nonaltruistic ones. From this rule, we infer that altruistic genotypes will persist in a population by forming a stable heritable polymorphism with nonaltruistic genotypes if rb = c makes inclusive fitness of the two morphs equal. We test this prediction using the data of 12 years of study on a cooperatively breeding bird, the Tibetan ground tit Pseudopodoces humilis, where helping is performed by males only and kin-directed. Individual variation in ever acting as a helper was heritable (h2 = 0.47), and the resultant altruism polymorphism remained stable as indicated by low-level annual fluctuation of the percentage of helpers among all adult males (24-28%). Helper's indirect fitness gains from increased lifetime reproductive success of related breeders statistically fully compensated for their lifetime direct fitness losses, suggesting that rb = c holds. While our work provides a fundamental support for Hamilton's idea, it highlights the equivalent inclusive fitness returns to altruists and nonaltruists mediated by rb = c as a theoretically and realistically important mechanism to maintain social polymorphism. [ABSTRACT FROM AUTHOR]

Competition between offspring can greatly influence offspring fitness and parental investment decisions, especially in communal breeders where unrelated competitors have less incentive to concede resources. Given the potential for escalated conflict, it remains unclear what mechanisms facilitate the evolution of communal breeding among unrelated females. Resolving this question requires simultaneous consideration of offspring in noncommunal and communal nurseries, but such comparisons are missing. In the Seychelles warbler Acrocephalus sechellensis, we compare nestling pairs from communal nests (2 mothers) and noncommunal nests (1 mother) with singleton nestlings. Our results indicate that increased provisioning rate can act as a mechanism to mitigate the costs of offspring rivalry among nonkin. Increased provisioning in communal broods, as a consequence of having 2 female parents, mitigates any elevated costs of offspring rivalry among nonkin: per-capita provisioning and survival was equal in communal broods and singletons, but lower in noncommunal broods. Individual offspring costs were also more divergent in noncommunal broods, likely because resource limitation exacerbates differences in competitive ability between nestlings. It is typically assumed that offspring rivalry among nonkin will be more costly because offspring are not driven by kin selection to concede resources to their competitors. Our findings are correlational and require further corroboration, but may help explain the evolutionary maintenance of communal breeding by providing a mechanism by which communal breeders can avoid these costs. [ABSTRACT FROM AUTHOR]

Although communicative complexity is often predicted to correlate with social complexity in animal societies, few studies have employed large-scale comparative analyses to test whether socially complex species have more complex systems of communication. I tested this social complexity hypothesis in birds (Class: Aves) using the large amount of natural history information that describes both vocal repertoire and social system in these species. To do so, I marshalled data from primary and secondary records of avian vocal repertoires (n = 253), and for each of the species in the dataset I recorded the reported repertoire size and associated species information. Using phylogenetic comparative methods, I found that cooperative breeding was a strong and repeatable predictor of vocal repertoire size, while other social variables, e.g. group size and group stability, had little or no influence on repertoire size. Importantly, repertoire sizes expanded concurrently with the evolution of cooperative breeding, suggesting a direct link between these two traits. Cooperatively breeding species devoted significantly more of their repertoire to contact calls and alarm calls. Overall, these results therefore lend support to the hypothesis that social complexity via behavioural coordination leads to increases in vocal complexity. [ABSTRACT FROM AUTHOR]

Waterfowl (Anatidae) are a group of birds in which parental care is performed by both parents (a pair) or, less often, by females only. Alternative social systems in this group have been recorded only occasionally. This paper describes three unusual cases of prolonged association between a pair and an additional male (the offspring or sibling of the primary pair) in breeding Whooper Swans (Cygnus cygnus). In all instances the three birds displayed no antagonistic behaviour towards family members, participated in territorial defence, and bred successfully. These cases are unusual in light of what is currently known about the social system of the highly territorial Whooper Swan in particular and of Anatidae in general, and are typical of cooperative breeding. This shows that swans may occasionally form an alternative social system. [ABSTRACT FROM AUTHOR]

Both mean group size ( MGS) and mean group density ( MGD) are critical indices to characterize a population of cooperatively breeding birds. When a population reaches its carrying capacity, both long-term MGS and long-term MGD will remain relatively stable. However, there has been little study of how these two variables relate. The Masked laughingthrush Garrulax perspicillatus is a cooperatively breeding bird living in fragmented habitats. During 2010 and 2012-2016, we used song playback to observe and confirm the group sizes and territory ranges of the birds and the data of bird presence to determine habitat suitability. By grouping the nearest territories according to their geographical coordinates, we divided the whole study area into 12 subareas and the whole population into 12 subpopulations. Then, we calculated both MGS and MGD for different time durations for each subpopulation. Finally, using MGD as independent variable and MGS as the dependent variable, we explored the correlations between MGS and MGD by fitting quadratic functions and modeling quadratic regression. Both MGS and MGD were averaged for different time durations and were cross-related. Our results show that the MGS for more than 2 years significantly correlated with MGD for more than 3 years in a reverse parabolic shape, differing from that of short-term effects. Our findings suggest that long-term MGD is a better predictor of long-term habitat quality and that long-term MGS is determined by long-term habitat quality in Masked Laughingthrushes. Based on above findings, we can infer that: (1) Long-term habitat quality determines the long-term MGS, but it sets no prerequisite for the status and source of group members; (2) Long-term MGS in certain populations is adapted to the corresponding level of long-term habitat quality, it facilitates us to predict the helper effects on current or future survival or reproduction in different situations. These findings and inferences are both helpful for us to understand the evolution of cooperative breeding. [ABSTRACT FROM AUTHOR]

The repayment hypothesis predicts that reproductive females in cooperative breeding systems overproduce the helping sex. Thanks to well-documented examples of this predicted sex ratio bias, repayment has been considered an important driver of variation in sex allocation patterns. Here we test this hypothesis using data on population brood sex ratios and facultative sex allocation from 28 cooperatively breeding bird species. We find that biased sex ratios of helpers do not correlate with production biases in brood sex ratios, contrary to predictions. We also test whether females facultatively produce the helping sex in response to a deficiency of help (i.e., when they have fewer or no helpers). Although this is observed in a few species, it is not a significant trend overall, with a mean effect size close to zero. We conclude that, surprisingly, repayment does not appear to be a widespread influence on sex ratios in cooperatively breeding birds. We discuss possible explanations for our results and encourage further examination of the repayment model. [ABSTRACT FROM AUTHOR]

In most bird species, dispersal distance from the natal territory to a breeding territory is greater for females than for males. Two main hypotheses have been proposed to explain sex-biased dispersal: 1) it serves as an inbreeding-avoidance mechanism or 2) it is linked to a sex difference in resource-holding potential and territory establishment. Additionally, in species where individuals delay dispersal and become subordinates in a natal territory, differences in benefits of philopatry (e.g. territory inheritance, own reproduction) may also affect sex-biased dispersal. We show that in the group-living Seychelles warbler, Acrocephalus sechellensis, females disperse further to obtain a breeding position than males do. However, we found no evidence that female-biased dispersal distance can be explained by the above-mentioned hypotheses: further dispersal does not lead to less-related partners, both sexes defend and can inherit a territory, and subordinate females are more likely to obtain some reproduction than subordinate males. Instead, we provide evidence for a little-explored hypothesis based on sex differences in dispersal costs: namely that extra-territorial forays, pursued to search for limited vacancies, are more costly for males in terms of increased mortality, although the exact mechanism for this is unclear. In line with differential dispersal costs, males foray less far than females and often wait for local dispersal opportunities, ultimately resulting in a shorter average dispersal distance. Our results may help future studies in explaining sex-biased dispersal in social and perhaps also non-social species, and we suggest some mechanisms that may explain why sex-biased dispersal differs between species. [ABSTRACT FROM AUTHOR]

Cooperative breeding is an extreme form of cooperation that evolved in a range of lineages, including arthropods, fish, birds, and mammals. Although cooperative breeding in birds is widespread and well-studied, the conditions that favored its evolution are still unclear. Based on phylogenetic comparative analyses on 3,005 bird species, we demonstrate here that family living acted as an essential stepping stone in the evolution of cooperative breeding in the vast majority of species. First, families formed by prolonging parent–offspring associations beyond nutritional independency, and second, retained offspring began helping at the nest. These findings suggest that assessment of the conditions that favor the evolution of cooperative breeding can be confounded if this process is not considered to include 2 steps. Specifically, phylogenetic linear mixed models show that the formation of families was associated with more productive and seasonal environments, where prolonged parent–offspring associations are likely to be less costly. However, our data show that the subsequent evolution of cooperative breeding was instead linked to environments with variable productivity, where helpers at the nest can buffer reproductive failure in harsh years. The proposed 2-step framework helps resolve current disagreements about the role of environmental forces in the evolution of cooperative breeding and better explains the geographic distribution of this trait. Many geographic hotspots of cooperative breeding have experienced a historical decline in productivity, suggesting that a higher proportion of family-living species could have been able to avoid extinction under harshening conditions through the evolution of cooperative breeding. These findings underscore the importance of considering the potentially different factors that drive different steps in the evolution of complex adaptations. [ABSTRACT FROM AUTHOR]

Loss and fragmentation of habitat can disrupt genetic exchange between populations, which is reflected in changes to the genetic structure of populations. The Grey-crowned Babbler (Pomatostomus temporalis) is a cooperatively breeding woodland bird, once common and widespread in south-eastern Australia. The species has suffered population declines of >90% across its southern distribution as a result of loss and fragmentation of habitat. We investigated patterns of genetic diversity and population structure of Grey-crowned Babblers in fragmented habitats at the southernmost extent of its range. We sampled blood from 135 individual Babblers from 39 groups stratified into six subpopulations in three regions. Genotypic data were used to estimate genetic diversity, population substructure, local relatedness and dispersal patterns. Individuals showed high heterozygosity within regions, and varying numbers of private alleles among regions suggested differences in levels of connectivity between regions. Four genetic clusters revealed population substructure consistent with treeless landscapes acting as strong barriers to gene flow. In contrast to previous studies, we identified a male-biased dispersal pattern and significant isolation-by-distance patterns for females at fine spatial scales. We recommend that conservation plans for this species incorporate opportunities to increase and enhance corridor areas to facilitate genetic exchange among subpopulations. [ABSTRACT FROM PUBLISHER]

The family of corvids differs from most other passerines by the significant number of species (at least 33) in which the feeding of nestlings and fledglings involves not only parents, but also individuals from their already grown broods (one-year-old and older). A review of the currently known data on cooperative breeding (or helping behavior) in corvids is given. This paper discusses factors that can contribute to the manifestation of delayed dispersion of young birds and the appearance of their helping behavior. It emphasizes the importance of long-term social bonds between parent birds and their offspring in delayed dispersion. At the heart of such social relationships is the tolerance of adult birds to their offspring and prolonged care for the young birds. The appearance of irregular helpers near the nests may be a prerequisite for the emergence of the helping behavior in certain family groups and populations. [ABSTRACT FROM AUTHOR]

Natural populations might exhibit resilience to changing climatic conditions if they already show adaptive flexibility in their reproductive strategies. In cooperative breeders, theory predicts that mothers with helpers should provide less care when environmental conditions are favourable, but maintain high investment when conditions are challenging. Here, we test for evidence of climate-mediated flexibility in maternal investment in the cooperatively breeding superb fairy-wren Malurus cyaneus. We focus on egg size because in this species egg size influences offspring size, and females reduce egg investment when there are helpers at the nest. We report that females lay larger eggs during dry, hot conditions. However, the effect of temperature is modulated by the presence of helpers: the average egg size of females with helpers is reduced during cooler conditions but increased during hot conditions relative to females without helpers. This appears to reflect plasticity in egg investment rather than among female differences. Analysis of maternal survival suggests that helped females are better able to withstand the costs of breeding in hot conditions than females without helpers. Our study suggests that females can use multiple, independent cues to modulate egg investment flexibly in a variable environment. [ABSTRACT FROM AUTHOR]

Why sexually mature individuals stay in groups as nonreproductive subordinates is central to the evolution of sociality and cooperative breeding. To understand such delayed dispersal, its costs and benefits need to be compared with those of permanently leaving to float through the population. However, comprehensive comparisons, especially regarding differences in future breeding opportunities, are rare. Moreover, extraterritorial prospecting by philopatric individuals has generally been ignored, even though the factors underlying this route to independent breeding may differ from those of strict philopatry or floating. We use a comprehensive predictive framework to explore how various costs, benefits and intrinsic, environmental and social factors explain philopatry, prospecting, and floating in Seychelles warblers ( Acrocephalus sechellensis). Not only floaters more likely obtained an independent breeding position before the next season than strictly philopatric individuals, but also suffered higher mortality. Prospecting yielded similar benefits to floating but lower mortality costs, suggesting that it is overall more beneficial than floating and strict philopatry. While prospecting is probably individual-driven, although limited by resource availability, floating likely results from eviction by unrelated breeders. Such differences in proximate and ultimate factors underlying each route to independent breeding highlight the need for simultaneous consideration when studying the evolution of delayed dispersal. [ABSTRACT FROM AUTHOR]

Divorce can be an important behavioral strategy to improve fitness. This is particularly relevant for species that are territorial year-round with continuous partnerships, where individuals face constraints on partner choice due to limited vacancies and dispersal opportunities. We tested several hypotheses for divorce in such a species, the cooperatively breeding bird Malurus coronatus. Based on 9 years of detailed information on dispersal and survival of 317 breeding pairs, we tested whether divorce is driven by inbreeding avoidance, by a better partner or territory, or by social variables (number of subordinates and fidelity of partners). We found that divorce is important to escape incest: incestuous pairs were substantially more likely to divorce (64%) than non-incestuous pairs (14%). However, incestuous pair bonds lasted up to a year, highlighting constraints on breeder dispersal. Non-incestuous pairs also divorced, but here the only predictor for divorce was the presence of extrapair offspring in a previous brood. Although reproductive failure did not trigger divorce, and reproductive success did not improve in the year following divorce, females that dispersed after divorce obtained higher quality territories, unlike females that dispersed after their partner died. Thus, divorce may be a strategy to improve long-term benefits associated with better territories. Some divorces appeared to be forced evictions by older females, although direct evidence for this is limited. Taken together, our findings demonstrate the complexity of factors that affect the occurrence of divorce when partner choice is constrained. [ABSTRACT FROM AUTHOR]

For many endotherms, communal roosting saves energy in cold conditions, but how this might affect social dynamics or breeding phenology is not well understood. Using chestnut-crowned babblers (Pomatostomus ruficeps), we studied the effects of nest use and group size on roosting energy costs. These 50 g cooperatively breeding passerine birds of outback Australia breed from late winter to early summer and roost in huddles of up to 20 in single-chambered nests. We measured babbler metabolism at three ecologically relevant temperatures: 5°C (similar to minimum nighttime temperatures during early breeding), 15°C (similar to nighttime temperatures during late breeding) and 28°C (thermal neutrality). Nest use alone had modest effects: even for solitary babblers at 5°C, it reduced nighttime energy expenditures by <15%. However, groupsize effects were substantial, with savings of up to 60% in large groups at low temperatures. Babblers roosting in groups of seven or more at 5°C, and five or more at 15°C, did not need to elevate metabolic rates above basal levels. Furthermore, even at 28°C (thermoneutral for solitary babblers), individuals in groups of four or more had 15% lower basal metabolic rate than single birds, hinting that roosting in small groups is stressful. We suggest that the substantial energy savings of communal roosting at low temperatures help explain why early breeding is initiated in large groups and why breeding females, which roost alone and consequently expend 120% more energy overnight than other group members, suffer relatively higher mortality than communally roosting group mates. [ABSTRACT FROM AUTHOR]

Individuals within animal groups may differ in personality and degree of familiarity raising the question of how this influences their social interactions. In Iberian magpies Cyanopica cooki , a portion of first-year males engage in cooperative behaviours and dispersal, allowing addressing this question. In this study, we first investigate the relationship between colony familiarity (native versus foreign) and reproductive status (breeding versus helping) of males during 21 years. Secondly, we measure the exploratory behaviour and monitor reproductive status of a sample of individuals with different colony familiarity during 2 years. Long-term monitoring revealed that foreign individuals were more likely breeders. The analysis on the subset of individuals in which exploratory behaviour was measured revealed a mediatory effect of exploratory behaviour in the association between colony familiarity and helping behaviour. Specifically, among foreign individuals, higher explorative males were more frequently involved in helping behaviour than lower explorative ones. Conversely, among native males, breeders were more explorative than helpers. Our results suggest that aspects of personality may mediate the value of familiarity in reproductive tasks in social species. [ABSTRACT FROM AUTHOR]

The evolution of cooperative breeding (CB) in birds has aroused intensive interest for decades, largely due to the paradox that some adults forgo independent breeding to help others. While much effort has been directed at understanding the adaptive significance of CB behavior, much less effort has been spent on understanding its origin. Ligon and Burt argued that the evolution of altriciality played a key role in the origin of CB since CB occurs more frequently in altricial lineages than expected if developmental mode and CB evolved independently and that both traits arose early in the avian tree of life. We mapped presence or absence of CB, and precocial or altricial development on a recent phylogeny of all birds to re-evaluate their conclusions. Our results suggest altriciality may be more recently derived than previously thought, and that CB species clustered in a derived land bird clade (especially within Passeriformes) where we reconstructed many gains and losses. We did find a link between cooperative breeding and altriciality. However, since CB also occurs in precocial species, has not evolved in many altricial clades, and may have evolved prior to altriciality (based on some classifications of which species have CB), it is not clear whether altriciality is linked to other factors, such as benefits to group living, that are necessary for the acquisition of CB behavior, or whether altriciality may have been a driving force in the evolution of CB itself. The relative importance of these other factors versus altriciality for the origin of CB needs to be considered. [ABSTRACT FROM AUTHOR]

Acorn woodpeckers, Melanerpes formicivorus , are cooperative breeders in which social groups consist of both nonbreeding helpers at the nest (offspring from prior reproductive attempts) and cobreeders of one or both sexes (usually siblings or a parent and his/her offspring). Regardless of composition, groups generally have one nest at a time at which all individuals participate in provisioning offspring. We tested the hypothesis that provisioning behaviour serves a signalling function used to gain social advantages within groups by enhancing dominance or social prestige, or by reducing the likelihood of being expelled from the group (‘pay-to-stay’). We found that birds adjusted their provisioning behaviour based on the activities of other group members by clumping their visits and by alternating their visits with other group members, thus synchronizing and coordinating provisioning within groups. Despite this evidence that acorn woodpeckers respond to the provisioning behaviour of other group members, analyses of feeding rates and patterns of overlap revealed no support for the hypothesis that provisioning functions as a signal to other group members in any of three ways: breeder males signalling to breeder females to increase their probability of mating; helpers signalling to other helpers to enhance their dominance or social prestige; or helpers signalling to breeders to reduce the probability that they will be considered ‘lazy’ and be evicted from the group. Our results add to previous studies that have thus far failed to support a signalling function for provisioning behaviour in avian cooperative breeders. [ABSTRACT FROM AUTHOR]

Experiments designed to quantify the effects of increasing numbers of carers on levels of offspring care are rare in cooperative breeding systems, where offspring are reared by individuals additional to the breeding pair. This paucity might stem from disagreement over the most appropriate manipulations necessary to elucidate these effects. Here, we perform both carer removal and brood enhancement experiments to test the effects of numbers of carers and carer:offspring ratios on provisioning rates in the cooperatively breeding chestnut-crowned babbler (Pomatostomus ruficeps). Removing carers caused linear reductions in overall brood provisioning rates. Further analyses failed to provide evidence that this effect was influenced by territory quality or disruption of group dynamics stemming from the removals. Likewise, adding nestlings to broods caused linear increases in brood provisioning rates, suggesting carers are responsive to increasing offspring demand. However, the 2 experiments did not generate quantitatively equivalent results: Each nestling received more food following brood size manipulation than carer removal, despite comparable carer:offspring ratios in each. Following an at-hatching split-design cross-fostering manipulation to break any links between prehatching maternal effects and posthatching begging patterns, we found that begging intensity increased in larger broods after controlling for metrics of hunger. These findings suggest that manipulation of brood size can, in itself, influence nestling provisioning rates when begging intensity is affected by scramble competition. We highlight that carer number and brood size manipulations are complimentary but not equivalent; adopting both can yield greater overall insight into carer effects in cooperative breeding systems. [ABSTRACT FROM AUTHOR]

When animals live near family members, this creates potential for incest and inbreeding depression, especially with unfamiliar kin. We examined incest avoidance when birds paired in kin groups and after dispersal in western bluebirds, Sialia mexicana, a cooperative breeder with a persistent, but low frequency of adult males helping at the nest. During their first winter, sons usually live in family groups comprised of parents, brothers, immigrant females, and more rarely, immigrant males and philopatric sisters. Sons usually pair with females that have joined their winter group, although some pair with females they encounter after dispersal. Incestuous pairing among relatives with relatedness =0.25 rarely occurred in either context, even considering extrapair fertilizations and other sources of unfamiliar kin. Sons pairing in their winter groups preferentially mated with immigrant females and actively avoided pairing with relatives. After dispersal into kin neighborhoods in spring, active incest avoidance was still required to explain low levels of incest with females within 600 m (2–3 territories) of where sons first bred, whereas absence of incest over larger distances could be explained by random mating. The probability of encountering a female relative within 600 m of where a male settled declined rapidly with dispersal distance to near zero for males dispersing 2 km from home. Although recognition is required to avoid incest when pairing in winter groups or settling near home, female-biased dispersal reduces likelihood of incest to near zero, even when males disperse relatively short distances (e.g., 2 km) from where they were born. [ABSTRACT FROM AUTHOR]

Changes in life history traits can reveal adaptations to changing environments. Red-cockaded Woodpeckers (Picoides borealis) are cooperative breeders that have specific reproductive habitat needs. We examined three separate sites in the southeastern United States to see how life history traits differed among isolated populations of Red-cockaded Woodpeckers from 1980 to 2013. We examined the life history traits group size, partial brood loss, number of fledglings, lay date, clutch size, and lifespan. Traits differed among sites, suggesting that populations were adapted to local conditions and different life history trade-offs were important under different environmental conditions at each site. At the two coastal sites in Florida and North Carolina, the family group sizes, lifespans, and partial brood loss were higher when compared to the inland site in North Carolina. Clutch size and number fledged were higher at the two northernmost sites when compared to the southern site. Identifying the differences in life history traits can allow more specific and effective management practices. [ABSTRACT FROM AUTHOR]

Understanding how sexual conflict influences male and female parental decisions is a long-standing problem in behavioral ecology. Until now, most research on sexual conflict over parental care has focused on behavioral mechanisms mediating the resolution of this conflict through negotiation between parents. Here, we review evidence suggesting that maternal effects that alter offspring phenotypes may provide females with a mechanism for manipulating male care. We show that empirical studies on the role of maternal androgens in birds with biparental care provide no support for female manipulation of male care. However, we argue that it would be premature to conclude that maternal androgens play no role in female manipulation of male care given methodological problems in previous work. We then identify a number of additional mechanisms by which females may manipulate male care, including egg components other than androgens, egg size, and egg coloration. We show that there is good evidence that egg coloration affects male care, suggesting that this mechanism warrants further research. We also highlight that current evidence is derived from studies using experimental design that target specific candidate mechanisms, such as maternal androgens. Given the multitude of candidate mechanisms, we discuss an alternative approach based on targeting ecologically relevant prenatal conditions, such as food availability, and monitoring subsequent effects on candidate mechanisms, offspring phenotypes, and male and female care. Finally, we argue that it is timely to extend this work beyond birds with biparental care to include other taxa and species with uniparental male care and cooperative breeding. [ABSTRACT FROM AUTHOR]

In cooperatively breeding species, in which non-breeding helpers assist in rearing the offspring of breeding individuals, conflicts of interest commonly occur between breeders and helpers over their respective contributions to offspring care. During such conflicts, breeders might use aggressive behavior to enforce contributions of helpers to offspring care, especially if helpers are not related to the breeders and their offspring and thus do not stand to gain indirect fitness benefits by helping. Using a combination of behavioral and genetic data, we investigated in the cooperatively breeding El Oro parakeet Pyrrhura orcesi (i) whether breeders are commonly dominant over helpers, (ii) whether they use aggressive behavior toward helpers to enforce offspring provisioning, and (iii) whether the relatedness of helpers to the nestlings affects the frequency of --or the reaction of helpers to--such aggressions. Even though breeders were generally dominant over helpers, we found no evidence for the enforcement of alloparental care. This finding was independent of the relatedness between helpers and nestlings, even though distantly related helpers overall contributed little to offspring care. We suggest that the inability of breeders to properly assess the work rates of their helpers at least partly explains the absence of enforcement. More generally, our results add to a body of evidence suggesting that enforcement might be an exceptional rather than a general mechanism underlying the expression of alloparental care in cooperatively breeding species. [ABSTRACT FROM AUTHOR]

Learning and innovation abilities have been studied extensively in flocking birds, but their importance and relevance in cooperatively breeding birds have been relatively unexplored. We studied the acquisition of novel foraging skills in 14 groups of wild, cooperatively breeding Arabian babblers (Turdoides squamiceps). While in a previous study we found that subordinate individuals were usually the first to learn to remove black rubber lids from a foraging grid, here we show that dominant individuals were the first to succeed in shifting from these black rubber lids to newly introduced white rubber lids. We also found that in all groups where one forager learned to shift to the white lids, the rest of the foragers also learned to do so, suggesting that this behaviour may be transmitted among group members. Although dominant individuals were almost always the first to remove white lids, once starting to remove white lids, dominants and subordinates learned equally well to prefer white over black lids based on differential reinforcement (food was provided only under white lids). Together with our previous study, our results suggest that differences in learning between dominants and subordinates may be task-specific, which may represent different cognitive strategies: subordinates may explore a more diverse range of foraging opportunities, while dominants may be better at generalizing from familiar tasks to similar ones. [ABSTRACT FROM AUTHOR]

Although theory developed to understand carer response rules in cooperative breeders typically predicts partial compensation, where additional investment by one carer is optimally met by incomplete reductions by the other, fully additive care is a viable alternative under particular conditions. Primary among these conditions is an opportunity for both existing and additional carers to gain comparable fitness from contributing to rearing offspring. That, in a number of cooperative birds, at least one parent often maintains its level of contribution to offspring rearing independent of carer numbers is supportive, but experimental evidence is lacking. Here, in naturally occurring groups of the cooperatively breeding chestnut-crowned babbler, Pomatostomus ruficeps , we found that provisioning rates of male carers were insensitive to the number of other males present; this resulted in an increase in total brood and per capita nestling provisioning rates across the range of total carer numbers tested (i.e. two – seven). Further, remaining male carers failed to change their provisioning rates following the temporary removal of one to three other males for up to 36 h, leading to significant decreases in total brood and per capita nestling provisioning. We found no obvious evidence to suggest that carer removals were otherwise disruptive and confounded the opportunity for remaining carers to respond. Our results confirm the existence of strongly additive care in cooperative breeders, and corroborate recent theory predicting that such response rules will arise when all carers in a group have the potential to contribute similarly to offspring success. [ABSTRACT FROM AUTHOR]

Cooperative breeding is a widespread and intense form of cooperation, in which individuals help raise offspring that are not their own. This behaviour is particularly well studied in birds, using both long-term and comparative studies that have provided insights into the evolution of reproductive altruism. In most cooperatively breeding species, helpers are offspring that remain with their parents beyond independency and help in the raising of younger siblings. However, many cooperatively breeding species are poorly studied, and in 152 species, this behaviour only has been observed infrequently (i.e., occasional cooperative breeding). Here we argue that the parental care mode of these 152 species needs to be treated with caution, as factors associated with occasional cooperative breeding may differ from those associated with "regular" cooperative breeding. In most cooperatively breeding species, helpers provide alloparental care at the nests of their parents or close relatives; however, only in one occasionally cooperatively breeding species do offspring remain into the next breeding season with their parents. Accordingly, different factors are likely to be associated with regular and occasional cooperative breeding. The latter behaviour resembles interspecific feeding (i.e., individuals feed offspring of another species), which occurs when birds lose their brood and begin feeding at a nearby nest, or when birds mistakenly feed at another nest. Thus, we advise researchers to exclude occasional cooperative breeders in comparative analyses until their status is clarified, or to categorize them separately or according to the typically observed parental care mode. This approach will increase the robustness of comparative analyses and thereby improve our understanding of factors that drive the evolution of cooperative breeding. [ABSTRACT FROM AUTHOR]

Nest predation is the most important source of reproductive failure for many bird species, thus placing nests in 'safe' locations that minimise predation risk is paramount to maximising fitness. After a nest predation event, some species have been shown to manage the risk of nest predation for subsequent re-nesting attempts by moving to a new location, placing re-nests in areas with increased cover, or changing the height above ground at which the re-nest is placed. The extent to which this is an adaptive behaviour for birds in general is not yet clear, as existing studies are almost exclusively restricted to northern hemisphere species and species that do not breed cooperatively. Here, we examined the re-nesting behaviour of Bell Miners (Manorina melanophrys), a species of honeyeater endemic to Australia that is both multi-brooded and also frequently re-nests soon after nesting failure; females can build up to five nests in a breeding season. We tested if these females managed within-season nest predation risk by changing nest site characteristics (height from ground and distance between nests) between successive nesting attempts. We found that female miners did indeed manage predation risk by reducing the height from the ground at which they placed re-nests following predation events, but contrary to our second prediction we found no difference in distances moved to re-nest after females experienced nest predation or successfully rearing young. [ABSTRACT FROM AUTHOR]

Cooperative breeding in birds typically occurs when offspring - usually males - delay dispersal from their natal group, remaining with the family to help rear younger kin. Sex-biased dispersal is thought to have evolved in order to reduce the risk of inbreeding, resulting in low relatedness between mates and the loss of indirect fitness benefits for the dispersing sex. In this review, we discuss several recent studies showing that dispersal patterns are more variable than previously thought, often leading to complex genetic structure within cooperative avian societies. These empirical findings accord with recent theoretical models suggesting that sex- biased dispersal is neither necessary, nor always sufficient, to prevent inbreeding. The ability to recognize relatives, primarily by learning individual or group-specific vocalizations, may play a more important role in incest avoidance than currently appreciated. [ABSTRACT FROM AUTHOR]

Signal reliability is a major focus of animal communication research. Aggressive signals are ideal for measuring signal reliability because the signal referent - attack or no attack - can be measured unambiguously. Signals of aggressive intent occur at elevated rates in aggressive contexts, predict subsequent aggression by the signaler, and elicit appropriate responses from receivers. We tested the 'predictive criterion' in smoothbilled anis, Crotophaga ani, by broadcasting one of two playback types ('ahnee' calls only or 'ahnee + hoot' calls), presenting a taxidermic mount, and observing the animals' behavior. Based on the hypotheses that 'hoot' calls and 'throat-inflation' displays signal aggressive intent, we predicted that they would be associated with attack, and that signaling rate would increase over the time period leading up to an attack. Indeed, both hoots and throat-inflation displays reliably predicted attack. The second prediction, that signaling rate increases in the time leading up to attack, was strongly supported for throat-inflation displays, which increased over the pre-attack period in both treatments. Hoots increased over the pre-attack period in ahnee playbacks but not in ahnee + hoot playbacks. Hierarchical signaling systems are characterized by early, lessreliable predictors of attack, and later, more reliable predictors of attack. During both natural and simulated interactions, the more-reliable throatinflation display tended to precede the less-reliable hoot call, suggesting that this signaling system is not hierarchical. In a comparison of 11 putative signals of aggressive intent in birds, the throat-inflation display had the second highest mutual information (reduction in uncertainty) among visual signals and non-passerine signals while hoots had below-average mutual information. Natural observations indicate that both hoots and throat-inflation displays occur in the context of aggressive between-group encounters, and hoots also occur during within-group interactions. Throat-inflation displays appear to be reliable indicators of aggressive intent, but the function of hoot calls is less clear. [ABSTRACT FROM AUTHOR]

Cooperatively breeding birds employ a variety of mating strategies, and we do not fully understand breeding group structure and the range of reproductive strategies used by group members. We examined group structure and parentage in a population of Brown-headed Nuthatches ( Sitta pusilla). We genotyped 346 adults and nestlings banded at 59 nests using nine microsatellite loci to determine parentage and relatedness and compared the results to field observations of marked individuals from 282 nests monitored from 2006-2010. Based on field observations, 23% of nests were cooperative, and only 13% of the cooperative groups had more than one helper. Consistent with field observations, genetic analyses indicated that 83% of helpers were related to at least one parent at the nest, and that most helpers were male. Extra-group paternity appeared to be common at nests of both pairs (45%) and cooperative groups (32%, but did not differ in frequency between the two nest types. Although male helpers unrelated to the breeding female might be expected to sire offspring in cooperative groups, we did not observe this phenomenon. Instead, we found one, and possibly two, cases of incestuous breeding involving related helpers. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses article in the issue on the topic of cooperative breeding in animals, birds, and insects and its evolutionary coexistence.

Cooperatively breeding species are typically long lived and hence, according to theory, are expected to maximize their lifetime reproductive success through maximizing survival. Under these circumstances, the presence of helpers could be used to lighten the effort of current reproduction for parents to achieve higher survival., In addition, individuals of different sexes and ages may follow different strategies, but whether male and female breeders and individuals of different ages benefit differently from the presence of helpers has often been overlooked. Moreover, only one study that investigated the relationship between parental survival and the presence of helpers used capture-mark-recapture analyses ( CMR). These methods are important since they allow us to account for the non-detection of individuals that are alive in the population but not detected, and thus, the effects on survival and recapture probability to be disentangled., Here, we used multi-event CMR methods to investigate whether the number of helpers was associated with an increase in survival probability for male and female breeders of different ages in the sociable weaver Philetairus socius. In this species, both sexes reduce their feeding rate in the presence of helpers. We therefore predicted that the presence of helpers should increase the breeders' survival in both sexes, especially early in life when individuals potentially have more future breeding opportunities. In addition, sociable weaver females reduce their investment in eggs in the presence of helpers, so we predicted a stronger effect of helpers on female than male survival., As expected we found that females had a higher survival probability when breeding with more helpers. Unexpectedly, however, male survival probability decreased with increasing number of helpers. This antagonistic effect diminished as the breeders grew older., These results illustrate the complexity of fitness costs and benefits underlying cooperative behaviours and how these may vary with the individuals' sex and age. They also highlight the need for further studies on the sex-specific effects of helpers on survival. [ABSTRACT FROM AUTHOR]

The way in which breeders respond to helping, in terms of either offspring production or their own survival, may reflect the adaptive aspects of a cooperative breeding system. We explore this issue using a 5-year study of the Ground Tit Pseudopodoces humilis, a facultative cooperative breeder in which 47% of socially monogamous pairs have between one and four close male relatives as helpers. We found that helped nests did not fledge more or heavier nestlings than unhelped nests, and male young from helped and unhelped nests were equally likely to recruit into the local breeding population. However, helped parents of both sexes had a higher probability of survival to the following year than did unhelped parents. These findings suggest that Ground Tit parents with helpers trade current reproduction for personal survival and future reproduction, a strategy favoured by selection to cope with harsh, unpredictable environments such as the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Cooperative breeding typically evolves within discrete, stable groups of individuals, in which group members derive direct and/or indirect fitness benefits from cooperative behaviour. In such systems, strong selection on group discrimination should emerge. Despite this prediction, relatively few studies have investigated the mechanism of group discrimination in cooperative vertebrates, and the results of many may be confounded by ‘expectancy violation’, since test individuals from which stimuli were derived remained in the group during experimentation. Here, we used a novel experimental protocol that eliminates this confounding effect in a test of group discrimination in cooperatively breeding chestnut-crowned babblers, Pomatostomus ruficeps , using long-distance contact calls. Long-distance contact calls were found to be individually specific, but to lack obvious group level signatures. Using dual playbacks of removed group and nongroup members, we found that these calls allow effective discrimination: groups unanimously approached the speaker broadcasting calls of group members and concomitantly increased their contact call rates. Together, our results suggest that group discrimination emerges from individual recognition. Additionally, the affiliative behaviour of group members towards playbacks of removed members contrasts with the aggressive responses towards nongroup members found in all other studies. One explanation for these differences stems from our elimination of expectancy violation, but further studies are required to verify this. [ABSTRACT FROM AUTHOR]

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