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Abstract

1. Helpers that invest energy in provisioning the offspring of related individuals stand to gain indirect fitness benefits from doing so. First, if the helper’s effort is additional to that of the parents (additive) the productivity of the current breeding attempt can be increased. Secondly, if the parents reduce their workload (compensation) this can result in future indirect fitness gains to the helper via increased breeder survival; termed ‘load-lightening’. 2. Long-tailed tits (Aegithalos caudatus) have a cooperative breeding system in which helpers assist kin and parents exhibit both additive and compensatory reactions in the presence of helpers. Offspring from helped nests are heavier and more likely to recruit into the breeding population, thus helpers gain indirect fitness benefits from increasing the productivity of the current breeding attempt. Despite breeders’ reduction of feeding effort in the presence of helpers, previous investigations found no subsequent increase in breeder survival. 3. The aim of this study was to test the hypothesis that load-lightening resulted in indirect fitness benefits for helpers. We used data from a 14-year study to investigate the provisioning rate, survival and future fecundity of male and female long-tailed tits that did and did not receive help at the nest. 4. We found an asymmetrical response to the presence of helpers at large brood sizes. Males reduced their feeding rate more than females, and this differential response was reflected in a significant increase in male survival when provisioning large broods assisted by helpers. We found no evidence of any increase in future fecundity for helped breeders. 5. The finding that males reduce their provisioning rate in the presence of helpers (at large brood sizes) to a greater degree than females, and that this is reflected in an increase in survival rate for males only, implies that the survival increase is caused by the reduction in work-rate rather than a non-specific benefit of a larger group size. 6. The marginal benefits of help for breeder survival are likely to be more difficult to identify than the increased productivity at helped nests, but should not be overlooked when investigating the potential indirect fitness gains that supernumeraries can accrue by helping.

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... Cooperative breeding can provide benefits to individual adults, as more individuals sharing the workload can buffer the effects of environmental stressors ('load-lightening', Ridley and Raihani 2007, Meade et al. 2010, Johnstone 2011, Wiley and Ridley 2016. Surprisingly, the presence of a helper (in all cases, male) did not correlate with increased overall parental care in this study. ...
... The addition of a helper male in our study only resulted in decreased provisioning by the breeding male, as the overall proportion of care provided by males altogether was indistinguishable between 2-and 3-adult groups (Fig. 4). Similarly, Meade et al. (2010) examined breeding behaviour for the cooperative breeding long-tailed tit Aegithalos caudatus, and found helper males only decreased the overall provisioning load of breeding males. While we were only able to distinguish between individual males in one territory, the helper (offspring from the previous year) provided 29.5% of provisions and the breeding male provided 24.8% of provisions, while the breeding female provided 45.7% of all provisions. ...
... The breeding male also experienced load-lightening in brooding from the addition of a helper male. To the best of our knowledge, no studies have examined time spent brooding of cooperative breeders for species where both sexes brood (as with rockjumpers), as in long-tailed tits only the females brood (Meade et al. 2010). ...
Article
Demonstrated negative effects of increased temperatures on avian reproductive success suggest a mechanism by which climate change may impact species persistence. High temperatures can result in reduced parental care and reduced nestling condition in passerines with dependent young, resulting in lowered fledging success and population recruitment. We examined provisioning rate and nestling condition in a South African mountain endemic, the Cape rockjumper Chaetops frenatus, whose population declines correlate with warming habitat. Our aim was to determine whether rockjumper reproductive success could be affected by high air temperatures. We set up video cameras on nests at three nestling age classes (≤ 7 days old; 8–12 days old; ≥ 13 days old) for 8 hours on 37 separate days. We successfully collected full‐day footage on 25 of the 37 days (four days with predation, eight with equipment failure). Nestlings were weighed at the beginning and end of each film day, barring the four days with mid‐day predation (n = 65 nestling measures from 33 of the 37 days). Average mass gain across all nestlings per nest was positively correlated with provisioning rate (0.78 g provisions−1 hr−1, CI: 0.26–1.30), and provisioning rate decreased at increasing temperatures (−0.08 provisions hr−1 °C−1, CI: −0.15 to −0.01). Daily change in mass of individual nestlings was negatively correlated with air temperatures above a significant temperature threshold (22.4°C; −0.30 g °C−1, CI: −0.40 to −0.19). This suggests nestling energy requirements were not being met on higher temperature days – perhaps because nestling energy and water demands for thermoregulation are elevated and provisioning rate is not correspondingly maintained or increased. These results suggest that higher temperatures negatively affect nestling mass gain. While in our study this did not directly affect fledging rates, it may affect post‐fledging survival.
... Some of these studies [10,11,14] explore impacts of temperature alongside variation in group size, but only Covas et al. [13] consider offspring survival across more than one development stage. This latter point is important, because specific drivers of survival can differ substantially between development stages [15][16][17]. ...
... Cooperative breeding, where more than two individuals rear a single brood [29], occurs in approximately 9% of bird species [30]. Benefits of cooperation include earlier fledging age and more broods raised per season [31], reduced costs of breeding for females [11,32], enhanced egg investment [33], increased fledgling recruitment [17,34], and the ability to raise overlapping broods [12,35]. Global comparative studies suggest that cooperative breeding evolved in unpredictable environments [36], facilitated the colonization of such environments [37] or prevented extinction under increasingly harsh conditions [38]. ...
... Higher rainfall periods are associated with greater food availability [20,89], which likely enhanced both provisioning rates to fledglings [90] and their ability to find food for themselves [91,92]. In cooperative breeders, survival of young during this stage often improves with increasing group size [34,51]: larger groups may provision more regularly [17] (but see [54]), better detect and repel predators [49], or access higher quality territories or nest sites [16]. We did not find a direct effect of group size on survival to independence at the brood scale. ...
Article
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An improved understanding of life-history responses to current environmental variability is required to predict species-specific responses to anthopogenic climate change. Previous research has suggested that cooperation in social groups may buffer individuals against some of the negative effects of unpredictable climates. We use a 15-year dataset on a cooperative breeding arid zone bird, the southern pied babbler Turdoides bicolor, to test (i) whether environmental conditions and group size correlate with survival of young during three development stages (egg, nestling, fledgling) and (ii) whether group size mitigates the impacts of adverse environmental conditions on survival of young. Exposure to high mean daily maximum temperatures (mean Tmax) during early development was associated with reduced survival probabilities of young in all three development stages. No young survived when mean Tmax > 38°C, across all group sizes. Low survival of young at high temperatures has broad implications for recruitment and population persistence in avian communities given the rapid pace of advancing climate change. Impacts of high temperatures on survival of young were not moderated by group size, suggesting that the availability of more helpers in a group is unlikely to buffer against compromised offspring survival as average and maximum temperatures increase with rapid anthropogenic climate change.
... Although there is likely to be a myriad of traits influencing helping behavior, a few key factors have emerged from existing research. For example, helpers have been observed to decrease their individual contributions as group size increases (Anava et al., 2001;Clutton-Brock et al., 2001;Russell et al., 2008;Meade et al., 2010); a behavior also shown by parents, known as load-lightening (Crick, 1992). Another prominent pattern among helpers is for one sex to contribute more to offspring care than the other (Cockburn, 1998;Ridley and Huyvaert, 2007;Koenig et al., 2011). ...
... When helpers were present, mothers reduced their investment in young, a finding that is in line with previous research demonstrating maternal load-lightening in other cooperatively breeding species (Crick, 1992;Meade et al., 2010;Zöttl et al., 2013b). Studies have demonstrated both theoretically (Johnstone, 2011) and empirically (Blackmore and Heinsohn, 2007;Ridley and Raihani, 2007;Meade et al., 2010) that when helpers reduce parental care load, parents can improve their overall fitness by reallocating resources to their own survival or future reproduction. ...
... When helpers were present, mothers reduced their investment in young, a finding that is in line with previous research demonstrating maternal load-lightening in other cooperatively breeding species (Crick, 1992;Meade et al., 2010;Zöttl et al., 2013b). Studies have demonstrated both theoretically (Johnstone, 2011) and empirically (Blackmore and Heinsohn, 2007;Ridley and Raihani, 2007;Meade et al., 2010) that when helpers reduce parental care load, parents can improve their overall fitness by reallocating resources to their own survival or future reproduction. However, although helpers elicited a compensatory response in mothers, the same was not found for fathers. ...
Article
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In cooperatively breeding species, the level of investment in young can vary substantially. Despite receiving considerable research attention, how and why investment in young varies with cooperatively breeding group members remains unclear. To investigate the causes of variation in care of young, we assessed patterns of both helper and parental behavior in the cooperatively breeding Western Australian magpie (Cracticus tibicen dorsalis). Observations of 19 helpers and 31 parents provisioning 33 broods raised in 11 different groups over two consecutive breeding seasons revealed substantial variation in offspring care behavior. Our results suggest that the level of investment in young by helpers is strongly influenced by group size, chick age, and individual helper traits (including foraging efficiency, age and sex). Helping behavior was facultative, and individuals from smaller groups were more likely to invest in helping behavior. Overall, the number of broods receiving help was lowest during the nestling phase and highest during the fledgling phase. Female helpers provided more care than both male and juvenile helpers. We found that mothers invest more time in offspring care than do fathers, however fathers increase their effort in the presence of helpers while mothers do not. Overall, helper care was additive to parental care and therefore helping behavior may be beneficial to the brood. Our research reveals that variation in offspring care in magpies is influenced by both social and individual traits.
... Conversely, when the dominants compensate for the care provided by helpers by reducing their amount of care, the total amount of care received by the offspring may remain similar. Such "load lightening" by helpers can reduce the costs of reproduction for the dominants (Bruintjes, Heg-Bachar, & Heg, 2013;Dixit, English, & Lukas, 2017;Heinsohn, 2004;Koenig & Walters, 2011;Meade, Nam, Beckerman, & Hatchwell, 2010;Scantlebury, Russell, McIlrath, Speakman, & Clutton-Brock, 2002;Sharp, English, & Clutton-Brock, 2013), which can lead to increased dominant survival (Cockburn et al., 2008;Hatchwell & Russell, 1996b;Heinsohn, 1992;Khan & Walters, 2002;Kingma et al., 2010) and increased future reproductive success (Brown & Brown, 1981;Russell, Brotherton, McIlrath, Sharpe, & Clutton-Brock, 2003;Woxvold & Magrath, 2005;Blackmore & Heinsohn, 2007; but see Meade et al., 2010). ...
... Conversely, when the dominants compensate for the care provided by helpers by reducing their amount of care, the total amount of care received by the offspring may remain similar. Such "load lightening" by helpers can reduce the costs of reproduction for the dominants (Bruintjes, Heg-Bachar, & Heg, 2013;Dixit, English, & Lukas, 2017;Heinsohn, 2004;Koenig & Walters, 2011;Meade, Nam, Beckerman, & Hatchwell, 2010;Scantlebury, Russell, McIlrath, Speakman, & Clutton-Brock, 2002;Sharp, English, & Clutton-Brock, 2013), which can lead to increased dominant survival (Cockburn et al., 2008;Hatchwell & Russell, 1996b;Heinsohn, 1992;Khan & Walters, 2002;Kingma et al., 2010) and increased future reproductive success (Brown & Brown, 1981;Russell, Brotherton, McIlrath, Sharpe, & Clutton-Brock, 2003;Woxvold & Magrath, 2005;Blackmore & Heinsohn, 2007; but see Meade et al., 2010). ...
... The observation that sex-specific investment changed over the course of the breeding event may suggest that other aspects, besides certainty of parentage, affect the symmetry of provisioning between sexes, as has been observed in other species (Cockburn et Meade et al., 2010). For example, females might reduce the costs of investment before the nestling period by decreasing egg size when assisted by helpers Dixit et al., 2017; but see Koenig, Walters, & Haydock, 2009). ...
Article
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In cooperatively breeding species, care provided by helpers may affect the dominant breeders’ investment trade‐offs between current and future reproduction. By negatively compensating for such additional care, breeders can reduce costs of reproduction and improve their own chances of survival. Alternatively, helper care can be additive to that of dominants, increasing the fledging fitness of the current brood. However, the influence helpers have on brood care may be affected by group size and territory quality. Therefore, the impact of helping needs to be disentangled from other factors determining offspring investment before conclusive inferences about the effect of help on additive and compensatory care can be made. We used 20 years of provisioning data to investigate the effect of helping on provisioning rates in the facultative cooperatively breeding Seychelles warbler Acrocephalus sechellensis. Our extensive dataset allowed us to statistically disentangle the effects of helper presence, living in larger groups and different food availability. We show compensatory and additive care (i.e., partial compensation) in response to helper provisioning. Helpers lightened the provisioning load of the dominant male and female and increased total provisioning to nestlings. This was irrespective of group size or territory quality (food availability). Moreover, our results illustrate sex‐specific variation in parental care over the course of the breeding event. We discriminate between temporal variation, group size, and territory quality processes affecting cooperative care and as such, gain further insight into the importance of these factors to the evolutionary maintenance of helping behavior.
... In addition, although helpers sometimes improve the immediate survival or condition of recipient offspring (e.g., Waser et al. 1994;Hodge 2005), the fitness benefits are not always apparent in the short term. Instead, helpers may have downstream effects on recipient fitness that become evident only in the long term, such as increased survivorship to breeding age , increased fecundity of helped offspring (Hodge 2005) or improved breeder survival rates (Meade et al. 2010). Helper effects may also be masked by subtle changes in breeder behavior and investment. ...
... For example, breeders may be the principal beneficiaries via reduced reproductive costs or "load-lightening," resulting in increased survivorship and/or future fecundity (Crick 1992). Such fitness benefit gains by helped breeders have been noted in several cooperative breeders, including long-tailed tits Aegithalos caudatus (Hatchwell and Russell 1996;Meade et al. 2010), white-fronted bee-eaters Merops bullockoides (Emlen and Wrege 1991), and splendid fairy-wrens Malurus splendens (Russell and Rowley 1988). In addition, in some species, breeders only partially reduce their effort so that they receive some benefit from "load-lightening" while offspring also receive additive care from helpers (Hatchwell 1999;Kingma et al. 2010). ...
... We also fitted an interaction between "helped" and "parent sex" because male and female parents may respond differently to provisioning by helpers (Hatchwell 1999). In addition, we fitted interactions between "helped" and brood size, and "helped" and nestling age terms (linear and quadratic) because the parental response to help may depend on the demands of the brood (e.g., Meade et al. 2010). We also included an interaction between "parent sex" and nestling age terms to allow for a difference in provisioning response to older nestlings between male and female breeders. ...
Article
Full-text available
Indirect fitness benefits gained through kin-selected helping are widely invoked to explain the evolution of cooperative breeding behavior in birds. However, the impact of helpers on productivity of helped broods can be difficult to determine if the effects are confounded by territory quality or if the benefit of helpers is apparent only in the long term. In riflemen Acanthisitta chloris, helping and group membership are effectively decoupled as adult helpers are individuals that have dispersed from their natal territory and live independently from breeders in “kin neighborhoods.” Nevertheless, helpers direct their care toward close relatives, suggesting that helping provides indirect fitness benefits. The aim of this study was to examine the benefits of helpers to recipient offspring in the rifleman, investigating both short- and long-term effects. The total amount of food delivered to nestlings in helped broods was greater than that received by broods without helpers. This did not result in any short-term increase in nestling mass or nestling body condition nor was there any reduction in length of the nestling period at helped nests. However, helpers were associated with a significant increase in juvenile recruitment, with twice the proportion of fledglings surviving to the next breeding season from helped broods relative to unhelped broods. Thus, helpers gain indirect fitness by improving the survival of kin, and in contrast to a previous study of riflemen, we conclude that kin selection has played a key role in the evolution of cooperative breeding in this species.
... Sometimes group members even assist in raising each other's offspring (Brown 1987;Koenig and Dickinson 2016), which can increase current reproduction (Emlen and Wrege 1991;Koenig and Walters 2011) or reduce the workload and thereby increase subsequent parental survival (Meade et al. 2010;Paquet et al. 2015). However, group members can also affect fitness negatively as the presence of extra group members can increase intra-specific competition for resources (Newton 1992), which might result in increased stress (Markham et al. 2015), reduced mating opportunities (Heg et al. 2008;Huchard and Cowlishaw 2011) and reduced survival (Brouwer et al. 2006). ...
... The marginal-and for most type of individuals, statistically non-significant-benefit of an extra group member on survival, was one of the most important determinants of RVs in both species. Previous studies have emphasized the expectation that group size effects on survival may be biologically most important, while statistically hardest to detect (Meade et al. 2010), and our study provides a first quantitative confirmation of this prediction. This result gives weight to the idea that the current focus in the literature on reproductive success, may paint a non-representative picture of the overall fitness patterns, and that integrating group size effects across multiple fitness components is a research priority. ...
Article
Group living can be beneficial when individuals reproduce or survive better in the presence of others, but, simultaneously, there might be costs due to competition for resources. Positive and negative effects on various fitness components might thus counteract each other, so integration is essential to determine their overall effect. Here, we investigated how an integrated fitness measure (reproductive values [RVs]) based on six fitness components varied with group size among group members in cooperatively breeding red-winged and superb fairy wrens (Malurus elegans and Malurus cyaneus, respectively). Despite life-history differences between the species, patterns of RVs were similar, suggesting that the same behavioral mechanisms are important. Group living reduced RVs for dominant males, but for other group members, this was true only in large groups. Decomposition analyses showed that our integrated fitness proxy was most strongly affected by group size effects on survival and was amplified through carryover effects between years. Our study shows that integrative consideration of fitness components and subsequent decomposition analysis provide much needed insights into the key behavioral mechanisms shaping the costs and benefits of group living. Such attribution is crucial if we are to synthesize the relative importance of the myriad group size costs and benefits currently reported in the literature.
... Empirical evidence is growing that females effectively lay smaller eggs (e.g. Paquet et al., 2013;Russell et al., 2007;Canestrari et al., 2011) or reduce their provisioning rates (Meade et al., 2010;Li et al., 2015) in relation to the presence or number of helpers in cooperative groups (e.g. Legge, 2000b;Paquet et al., 2013). ...
... However, both past and current empirical studies typically focus on load-lightening strategies during nestling provisioning only (e.g. Covas et al., 2008;Meade et al., 2010;Hatchwell, 1999;Crick, 1992), while largely neglecting pre-hatching strategies. A recent meta-analysis on pre-hatching investment in cooperatively breeding vertebrates reports only 12 studies on 10 species (Dixit et al., 2017). ...
... However, a reduction in individual effort does not necessarily result in ineffective collective action, as individuals in large groups may be more likely to participate when there are long-term payoffs of remaining within a competitive social group (i.e. via 'group augmentation, ' Langergraber et al., 2017). Moreover, participants in large groups may be driven to maximize the group's aggregate effort in order to increase the survival or female fecundity of group members at lower cost to individuals than in smaller groups (i.e. via 'load lightening, ' Meade, Nam, Beckerman, & Hatchwell, 2010). ...
... Thus, when there are high costs of interacting with another group (reflected by high levels of aggression), more individuals may participate, perhaps to increase the competitive success of the group, or avoid the costs of losing. The reduction in individual participation in larger groups may therefore reflect load lightening to maintain group augmentation, rather than the collective action problem, where competitive ability is compromised by low participation (Langergraber et al., 2017;Meade et al., 2010). Probability that a female would direct agonistic behaviour towards an extragroup gorilla ...
Article
In group-living species, encounters with extragroup rivals can be one of the riskiest actions in which individuals participate. Different group members often have different incentives to participate during intergroup interactions, and individuals with fewer payoffs of competition, including those of the smaller sex and/or lower rank, may ‘free-ride’ to avoid the costs of conflict. However, there is little evidence for how different types of intergroup interactions (e.g. interactions that do not involve conflict) can influence the participation of individuals. We examined the ecological, demographic and social predictors of individual participation in interactions between 14 fully habituated mountain gorilla groups in Volcanoes National Park, Rwanda from 2003 to 2015. The probability of an individual participating decreased with group size but remained relatively high in aggressive interactions and in multimale groups, illustrating the potential for ‘load lightening’ among group members. Males with fewer mating opportunities participated less often than males with more mating opportunities; however, male participation was significantly higher than female participation across all types of intergroup interactions. Females were more likely to be involved in aggressive interactions with solitary males, possibly to avoid the potential cost of infanticide if a resident male is killed or injured. Both sexes demonstrated more affiliative behaviours towards familiar groups, indicating a benefit of maintaining social relationships with familiar groups. Individuals show considerable variation in behaviour during intergroup interactions, and our results suggest that this variation is primarily driven by intergroup familiarity and individual reproductive benefits, both of which may have long-term consequences for individual fitness.
... This latter pattern is expected in species with high chances of nest failure due to starvation where parents would rarely be able to breed successfully without help (Hatchwell 1999;Liebl et al. 2016; but see Legge (2000b)). Another possibility is the occurrence of partial compensation (Russell et al. 2008;Kingma et al. 2010;Meade et al. 2010;Brouwer et al. 2014). In this case, although the parents may reduce their effort somewhat, they can still gain a higher overall investment in the offspring due to an increase in auxiliary effort. ...
... Alternatively, assisted breeders may reduce their own provisioning effort, but this would not change the overall provisioning rate, because the investment made by the auxiliaries may compensate the reduction in the care provided by the parents (Brown et al. 1978;Legge 2000b;Khan and Walters 2002). Studies have shown that the occurrence of an increase in the productivity is possible even with the reduction of parental workload (Kingma et al. 2010;Meade et al. 2010). In redwinged fairy wrens (Malurus elegans), the social environment affects the probability of load lightening. ...
Article
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In cooperative species, parental investment may be shared with auxiliaries. Kin selection and other types of benefits have been proposed to explain the evolution of helping behavior. Auxiliaries are expected to be more helpful when closely related to the breeders. In this context, breeders may adjust parental investment in at least three ways: (a) reducing their effort and being compensated by the auxiliaries’ investment (compensatory effect); (b) maintaining their effort, with an increase in total investment (additive effect); or (c) partial compensation, i.e., a decrease in care by the parents but not by as much as the increase in care from the auxiliaries. We studied the cooperative species Colaptes campestris campestris and tested the following hypotheses: (1) partial compensation effect occurs, (2) parents modulate their investment relative to the auxiliaries’ investment, (3) auxiliaries adjust their investment according to their relationship to the offspring, and (4) groups whose members are in better physical condition fledge more young or these are in better condition. We determined relatedness within groups and monitored parental and alloparental behavior during breeding. Breeders in cooperative groups presented the same investment as unattended breeders. Restricting the analysis to cooperative groups revealed that the investment made by auxiliaries reflected their relatedness to the young and positively affected the investment by breeders. Results suggest that a partial compensation occurs in the species, with breeders reducing their effort despite the small increase in overall nest investment. Results highlight the importance of kin selection in the evolution of cooperative breeding in campo flickers. Significance statement Cooperatively breeding birds may have auxiliaries that help rear their brood. The evolution of helping behavior may derive from kin selection, where auxiliaries could gain a genetic benefit by helping to rear kin, which occurs when groups are composed of closely related individuals. However, it is often the case that some offspring may not be closely related to the auxiliaries due to the species’ mating system. We used the cooperatively breeding campo flickers to investigate whether and how the presence of auxiliaries might affect parental care patterns and nest productivity. We found that breeders did not reduce their investment in the presence of auxiliaries and that cooperative groups present the same overall investment when compared with unassisted pairs, indicating that the investment made by auxiliaries was not large enough to affect the total investment nor the breeders’ investment. Our results also show that auxiliaries increased their investment when they were more closely related to the brood.
... Because male long---tailed tits reduce effort more in response to helpers then females do [11], it is possible that there is a sex difference in sensitivities to social effects. To test this we fit a series of categorical random interaction models where an individual'ʹs social effect varied either as a function of its own sex or its partner'ʹs sex. ...
... ~ Norm(0, !,male ! ). Given previous findings that males reduce effort in the presence of helpers more than females do [11], if there is a difference then we would expect that males would be the more responsive sex. ...
... Second, they can increase the potential future production of non-descendent kin during the same (second broods) or subsequent breeding seasons, by increasing the condition or survival of their parents (Khan and Walters 2002;Li et al. 2015). This can occur by reducing the parental reproductive investment, for example, in eggs or nestling feeding (Meade et al. 2010), whereby helpers compensate for this lower investment with no net reproductive cost for the parents ("load-lightening"; Crick 1992). ...
Article
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In cooperatively breeding species, group members may derive multiple benefits from helping to raise other individuals’ offspring, yet not all individuals do so. In this study, we tested predictions from the “kin selection”, “pay-to-stay”, “group augmentation” and “skills” hypotheses, to explain why group members feed nestlings of breeding placid greenbuls (Phyllastrephus placidus). In our study population, about 70% of the breeding pairs were accompanied by subordinates, and in 60% of these cases at least one subordinate helped in provisioning nestlings. In total, 80% of the subordinates were related to one or both breeders. In accordance with the “kin selection” hypothesis, and contrary to the “pay-to-stay” hypothesis, all the helpers were first-order kin of the breeding female (although relatedness to the breeding male did not explain variation in helping) and the presence of helpers was associated with increased survival of the breeding pair. However, the propensity to help varied among group members, as 46% of group members related to the breeding female did not feed nestlings. Younger helpers fed offspring more often than older ones, supporting the “skills” and “group augmentation” hypotheses. However, support for the “group augmentation” hypothesis was mixed since subordinate sex and group size did not explain additional variation in helping propensity and effort. We argue that in addition to indirect and direct benefits, also the costs of helping as well as other types of helping aside from provisioning must be considered to better understand variation in helping behavior.
... Indeed, in some species (including pied babblers), parents may terminate care in young before helpers do (Pike, Ashton, Morgan, & Ridley, 2019;. Second, with multiple adults present to invest in young, load-lightening behavior (where there is no net decrease in the amount of care provided to young, but less contributed per adult in larger groups (Crick, 1992;Heinsohn, 2004;Meade, Nam, Beckerman, & Hatchwell, 2010;van Boheemen et al., 2019)) may occur. This results in less effort per breeding attempt for individuals living in groups compared to pairs and may reduce the costs of breeding. ...
Chapter
While considerable evidence exists that extreme climate events such as high temperatures and drought are becoming more common, there is growing recognition that we have limited empirical evidence on how wild animals are able to behaviorally and physiologically adjust to these potentially rapid changes. Despite considerable lab-based research on thermal physiological processes in animals, there is relatively little field-based research on how thermal stress affects physiology and behavior in wild animals. Directly relating physiological state to behavioral change is an important step in understanding the ability of species to adapt to changing climatic conditions and is therefore an important research gap to address during both the current and predicted future rapid changes in climate. Given that the ability of animals to adjust to changing conditions can directly impact their fitness, understanding the behavioral and demographic responses of animal populations to current climate events may be an essential way to determine future population viability. By synthesizing the long-term behavioral research on the pied babbler (Turdoides bicolor), conducted over the last 18 years, we determine the potential impact of climate change through an examination of behavioral responses to social and environmental factors. By combining our detailed behavioral, demographic and physiological research, we use the pied babbler as a model species to highlight the incredible value of (a) long-term behavioral research and (b) studying populations under natural conditions, to help understand the potential impacts of climate change on wild animals.
... Second, helpers can increase the potential future production of non-descendent kin during the same (second broods) or subsequent breeding seasons, by increasing the condition or survival of related breeders (Khan and Walters 2002;Li et al. 2015). This can be achieved, for example, through reduced reproductive investment by breeders, such as reduced egg size or feeding frequencies (Meade et al. 2010), where helpers compensate for such a reduction with no net cost to current reproductive outcome ('load-lightening'; Crick 1992). Third, helpers can decrease the variance in reproductive success which may minimize the probability of reproductive failure and reduce the negative impact of demographic and environmental stochastic events ('bet-hedging'; Lehmann and Balloux 2007;Rubenstein 2011). ...
... Breeders may compensate for the presence of helpers by reducing their investment (load lightening; e.g., Hatchwell and Russell 1996;Legge 2000;Balshine et al. 2001), which can increase their subsequent survival Cockburn et al. 2008;Paquet et al. 2015) or reduce intervals between reproductive attempts (Woxvold and Magrath 2005;Blackmore and Heinsohn 2007). In the absence of load lightening, or when compensation is incomplete, helpers will increase overall parental effort so that offspring receive greater total care (additive care; e.g., Clutton-Brock et al. 2001;Doerr and Doerr 2007), which can increase offspring growth (Hodge 2005) or productivity of the dominant breeders (Emlen and Wrege 1991;Kingma et al. 2010;Meade et al. 2010). Overall, there is thus ample potential for helpers to not only have short-term effects on current reproduction but also long-term effects on future reproduction (Brouwer et al. 2012). ...
... One prominent explanation for the occurrence of cooperative breeding in birds is that it represents a 'bet-hedging' strategy (Rubenstein, 2011): breeding individuals share the costs of reproduction with helpers, enabling them to breed successfully even when conditions are poor (Rubenstein and Lovette, 2007). Cooperation may therefore moderate impacts of climate change via task-partitioning (Clutton-Brock et al., 2004;, improved access to resources (Golabek et al., 2012;Ebensperger et al., 2016), or load-lightening (reductions in individual workload in response to the presence of helpers; Crick, 1992;Hatchwell, 1999;Meade et al., 2010;Mumme et al., 2015;Langmore et al., 2016). ...
Article
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Climate change is affecting animal populations around the world and one relatively unexplored aspect of species vulnerability is whether and to what extent responses to environmental stressors might be mitigated by variation in group size in social species. We used a 15-year data set for a cooperatively breeding bird, the southern pied babbler Turdoides bicolor, to determine the impact of temperature, rainfall and group size on body mass change and interannual survival in both juveniles and adults. Hot and dry conditions were associated with reduced juvenile growth, mass loss in adults and compromised survival between years in both juveniles (86% reduction in interannual survival) and adults (60% reduction in interannual survival). Individuals across all group sizes experienced similar effects of climatic conditions. Larger group sizes may not buffer individual group members against the impacts of hot and dry conditions, which are expected to increase in frequency and severity in future.
... Self-organized grouping behavior is a ubiquitous phenomenon in the animal kingdom where the many benefits offered by collective motion include cooperative hunting (Bailey et al (2013)), breeding (Meade et al (2010)), vigilance ), enhanced thermoregulation (Scantlebury et al (2006)) and predator defense (Hamilton (1971), Jakobsen and Johnsen (1988), Milinski (1979), Quinn and Cresswell (2006)). While a plethora of studies have been performed in this regard, the dynamics of schooling motion itself bears many open questions, attracting scientists from a wide range of disciplines. ...
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Self-organizing motion is an important yet inadequately understood phenomena in the field of collective behavior. For birds flocks, insect swarms, and fish schools, group behavior can provide a mechanism for defense against predators, better foraging and mating capabilities and increased hydro/aerodynamic efficiency in long-distance migration events. Although collective motion has received much scientific attention, more work is required to model and understand the mechanisms responsible for school initiation and formation, and information transfer within these groups. Here we investigate schooling of Black Tetra (Gymnocorymbus ternetzi) fish triggered by startle stimuli in the form of approaching objects. High-speed video and tagging techniques were used to track the school and individual members. We then measured several variables including reaction times, group formation shapes, fish velocity, group density, and leadership within the group. These data reveal three things: 1) information propagates through the group as a wave, indicating that each fish is not reacting individually to the stimulus, 2) the time taken for information to transfer across the group is independent of group density, and 3) information propagates across large groups faster than would be expected if the fish were simply responding to the motion of their nearest neighbor. A model was then built wherein simulated fish have a simple `stimuli/escape' vector based on a hypothetical field of vision. The model was used to simulate a group of individual fish with initial conditions, size, and stimuli similar to the biological experiments. The model revealed similar behavior to the biological experiments and provide insights into the observed patterns, response times, and wave speeds.
... We additionally consider the influence of group size on reproductive effort and success, and whether effects of high temperatures or drought were moderated by group size. Cooperative species may respond differently to external stressors than non-cooperative species, because reproductive outcomes can be affected by both the presence and behavior of other group members (Crick, 1992;Cockburn et al., 2008;Meade et al., 2010;Langmore et al., 2016;Wiley and Ridley, 2016). We predict that high temperatures and drought experienced within a breeding season will suppress both reproductive effort and success, and that pied babblers will compensate for this suppression by increasing investment in reproductive effort and success in breeding seasons that follow hot and dry conditions. ...
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Variation in weather patterns can influence reproductive effort and success not only within but also between breeding seasons. Where environmental conditions can be highly variable between years, the weather, and particularly extreme weather events such as heat waves and droughts, may exert a strong influence on reproductive effort (number of breeding attempts) and success (number of surviving young) from one breeding season to the next. We used a 15-year dataset for a cooperatively breeding bird, the southern pied babbler Turdoides bicolor, to determine the impact of high temperatures and drought on reproductive effort and success. We tested the influence on reproductive effort and success of mean daily maximum air temperature and drought both within a breeding season, to determine the relative importance of current conditions, and during the previous breeding season, to determine the relative importance of compensatory effects in response to prior conditions. Reproductive effort and success were lower during breeding seasons characterized by drought, and higher in the breeding seasons that followed droughts, but were not predicted by mean daily maximum temperatures measured over the full length of the breeding season. We provide evidence of compensatory breeding following drought in a bird species endemic to a semi-arid ecosystem and suggest that compensatory mechanisms may be an important part of both long-term population persistence and post-drought population recovery.
... prospecting interactions prior to juvenile dispersal; Kesler andHaig 2007, Cox and) that promote larger group sizes over time (Newton 1998). Positive group-size effects on productivity are so large in many cooperatively breeding birds they can offset negative effects of competition on productivity (Courchamp et al. 1999, Meade et al. 2010, even in low quality habitat (Cusick et al. 2018). This could have important implications for conservation of cooperative breeders with narrow habitat requirements because future declines in productivity may reflect density-dependent competition and small group sizes, rather than habitat degradation (Heuck et al. 2017). ...
... Hatchwell and Russell 1996;Hatchwell 1999;Valencia et al. 2006;Koenig and Walters 2011;Lu et al. 2011), the question of whether the presence of helpers affects parental food allocation among offspring has been neglected. Because helpers often increase food delivery to broods (Wilkinson and Brown 1984;Doerr and Doerr 2007;Preston et al. 2016) and/or lighten the load of parents (Hatchwell and Russell 1996;Caffrey 1999;Meade et al. 2010), parents may be expected to adjust food allocation among offspring accordingly. For example, they may be more concerned about nestling need when they are better able to provide care (Caro et al. 2016). ...
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Natural selection should favor adoption of parental strategies that maximize fitness when allocating investment among offspring. In birds, begging displays often convey information of nestling need and quality, allowing parents to make adaptive food allocation decisions. We investigated how adults utilized cues likely to represent nestling competitive ability (begging position) and need (begging intensity) and a cue independent of nestling control (nestling sex) to distribute food among nestlings in a facultative cooperative breeder, the black-throated tit (Aegithalos concinnus). We found that parents reduced their efforts when helped, suggesting that parents of helped broods would have the potential to satisfy nestling needs more than unhelped parents. This suggestion was supported by the fact that nestling mass increased faster in helped than in unhelped nests. We found no effect of nestling sex on food allocation, but, as predicted, we found that adults responded differently to begging signals in relation to the presence of helpers and brood size. First, helped parents were more responsive to nestling begging intensity than parents without helpers. Second, female parents and helpers had a stronger preference for nestling begging position in large than in small broods. Third, the preference for nestling begging position was greater for unhelped than for helped female parents. These results provide evidence that carers adjust their preference for different offspring begging signals based on availability of food resources.
... This could be accomplished for RCWs by enhancing demographic connectivity through strategic placement of recruitment clusters within 400 m of existing clusters occupied by RCW groups (Garabedian et al., 2018b). Based on results from this study, QCA may be well-suited for synthesis of habitat-fitness data for group-living species like RCWs and brown treecreepers because group size and breeder age can have a large positive effect on fitness independent of habitat conditions (Meade et al., 2010). Because QCA is not constrained by collinearity, we could identify how large and medium pines can have consistent positive effects on RCW group fitness in conjunction with group size and hardwood midstory conditions, without fitting compound habitat variables or introducing bias from collinearity. ...
Article
Meta-analyses are powerful tools for synthesizing wildlife-habitat relationships, but small sample sizes and complex species-habitat relationships often preclude correlative meta-analyses on endangered species. In this study, we demonstrate qualitative comparative analysis (QCA) as a tool that can reliably synthesize habitat-fitness relationships from small sample sizes for species with narrow habitat requirements. We apply QCA to results from a habitat threshold regression tree model and identify habitat thresholds with consistent positive effects on fitness of the federally endangered red-cockaded woodpecker (Dryobates borealis; RCW) on the Savannah River Site, USA. We reformulated regression tree results in a QCA framework to examine the consistency of threshold effects on RCW fledgling production at the individual group level (n = 47). Synthesizing regression tree results with QCA revealed alternative combinations of habitat thresholds that in conjunction with group size consistently led to above-average fledgling production for 41 of 47 (88%) individual RCW groups. Importantly, QCA identified unique combinations of habitat thresholds and group size related to above-average fledgling production that were not retained in the regression tree model due to small sample sizes. Synthesizing a small habitat-fitness dataset using QCA provided a tractable method to identify unique combinations of habitat and group size conditions that are consistently important to individual fitness, but may not be detected by meta-analyses that can be biased by small sample sizes. QCA offers a viable approach for synthesis of habitat-fitness relationships and can be extended to address many complex issues in endangered species recovery when correlative meta-analyses are not possible.
... P < 0.0001), indicating that they tend to be mutually exclusive activities (too few females gained indirect fitness for an equivalent analysis). This makes intuitive sense because an individual long-tailed tit cannot gain both direct and indirect fitness (i.e., breed successfully and help) within the same season because helping is contingent on failed breeding, and the lifespan of long-tailed tits is short [annual adult survival rate is 0.55 (33)], with the result that approximately half of all birds experience only a single breeding season. ...
Article
Significance How far individuals disperse from their birth site has profound consequences for the genetic structure of populations and for individual fitness, affecting the degree of gene flow between populations and the extent to which relatives and nonrelatives interact socially. Spatial clustering of kin arising from limited dispersal facilitates kin-selected cooperation and is considered an important step in the evolution of cooperative breeding. However, determination of the fitness consequences of dispersal in wild populations has proved extremely challenging. Here, we use data from a long-term study of long-tailed tits to quantify the fitness payoffs of dispersal. We show that females’ reproductive success increases with dispersal distance and that, for males, cooperation with kin generates fitness benefits that favor limited natal dispersal.
... Conversely, delayed juvenile dispersal improves the survival of tending mothers in the subsocial spider Anelosimus studiosus (Jones & Parker, 2002), a finding that might reflect benefits of offspring investment into prey capture or into the maintenance of the communal web. Indeed, offspring assist in web construction in many social spiders (Yip & Rayor, 2014), suggesting that mothers could regularly benefit by reducing their own investment (such 'load lightening' is well known in cooperative breeders, where helpers can often gain indirect fitness benefits by enabling their parents to produce more siblings; Crick, 1992;Meade et al., 2010;Johnstone, 2011). Although such benefits of offspring assistance might be concealed by the costs of parental care, they could nevertheless have a significant impact on the evolution of family interactions and, more generally, on the emergence of social life in family units (see Section IV). ...
Article
Family life forms an integral part of the life history of species across the animal kingdom and plays a crucial role in the evolution of animal sociality. Our current understanding of family life, however, is almost exclusively based on studies that (i) focus on parental care and associated family interactions (such as those arising from sibling rivalry and parent‐offspring conflict), and (ii) investigate these phenomena in the advanced family systems of mammals, birds, and eusocial insects. Here, we argue that these historical biases have fostered the neglect of key processes shaping social life in ancestral family systems, and thus profoundly hamper our understanding of the (early) evolution of family life. Based on a comprehensive survey of the literature, we first illustrate that the strong focus on parental care in advanced social systems has deflected scrutiny of other important social processes such as sibling cooperation, parent–offspring competition and offspring assistance. We then show that accounting for these neglected processes – and their changing role over time – could profoundly alter our understanding of the origin and subsequent evolution of family life. Finally, we outline how this ‘diachronic’ perspective on the evolution of family living provides novel insights into general processes driving the evolution of animal sociality. Overall, we infer that the explicit consideration of thus‐far neglected facets of family life, together with their study across the whole diversity of family systems, are crucial to advance our understanding of the processes that shape the evolution of social life.
... Guindre-Parker and D.R. Rubenstein 2017, unpublished data), so we would not expect breeders to reduce their care unless they gained future fitness benefits that compensated for this loss in current reproductive success. Second, the magnitude of loadlightening observed in our study is similar to the magnitude observed in other species where future fitness benefits were documented (i.e. a twofold difference in provisioning or nest guarding with the smallest relative to largest contingent of alloparents) [13,50]. Together, this evidence suggests that loadlightening measured in our study system is likely to be biologically meaningful. ...
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Although cooperatively breeding vertebrates occur disproportionately in unpredictable environments, the underlying mechanism shaping this biogeographic pattern remains unclear. Cooperative breeding may buffer against harsh conditions (hard life hypothesis), or additionally allow for sustained breeding under benign conditions (temporal variability hypothesis). To distinguish between the hard life and temporal variability hypotheses, we investigated whether the number of alloparents at a nest increased reproductive success or load-lightening in superb starlings (Lamprotornis superbus), and whether these two types of benefits varied in harsh and benign years. We found that mothers experienced both types of benefits consistent with the temporal variability hypothesis, as larger contingents of alloparents increased the number of young fledged while simultaneously allowing mothers to reduce their provisioning rates under both harsh and benign rainfall conditions. By contrast, fathers experienced load-lightening only under benign rainfall conditions, suggesting that cooperative breeding may serve to take advantage of unpredictable benign breeding seasons when they do occur. Cooperative breeding in unpredictable environments may thus promote flexibility in offspring care behaviour, which could mitigate variability in the cost of raising young. Our results highlight the importance of considering how offspring care decisions vary among breeding roles and across fluctuating environmental conditions.
... The avian literature is replete with examples of repeatability and coordinated care between mated individuals (Schwagmeyer et al. 2002;Johnstone and Hinde 2006;Nakagawa et al. 2007;Meade et al. 2010;Johnstone 2011;Schuett et al. 2011;Low et al. 2012;Wetzel and Westneat 2014;Bebbington and Hatchwell 2015). However, offspring of mammalian mothers gestate internally and are dependent on milk provided solely by the mother early in life (King et al. 2013). ...
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In biparental systems, sexual conflict over parental investment predicts that the parent providing care experiences greater reproductive costs. This inequality in parental contribution is reduced when offspring survival is dependent on biparental care. However, this idea has received little empirical attention. Here, we determined whether mothers and fathers differed in their contribution to care in a captive population of coyotes (Canis latrans). We performed parental care assays on 8 (n = 8 males, 8 females) mated pairs repeatedly over a 10-week period (i.e., 5-15 weeks of litter age) when pairs were first-time breeders (2011), and again as experienced breeders (2013). We quantified consistent individual variation (i.e., repeatability) in 8 care behaviors and examined within-and among-individual correlations to determine if behavioral plasticity within or parental personality across seasons varied by sex. Finally, we extracted hormone metabolites (i.e., cortisol and testosterone) from fecal samples collected during gestation to describe potential links between hormonal mechanisms and individual consistency in parental behaviors. Parents differed in which behaviors were repeatable: mothers demonstrated consistency in provisioning and pup-directed aggression, whereas fathers were consistent in pup checks. However, positive within-individual correlations for identical behaviors (e.g., maternal versus paternal play) suggested that the rate of change in all behaviors except provisioning was highly correlated between the sexes. Moreover, positive among-individual correlations among 50% of identical behaviors suggested that personality differences across parents were highly correlated. Lastly, negative among-individual correlations among pup-directed aggression, provisioning, and gestational testosterone in both sexes demonstrated potential links between preparental hormones and labile parental traits. We provide novel evidence that paternal contribution in a biparental species reaches near equivalent rates of their partners.
... In contrast to the literature on human alloparenting, investigators of cooperatively breeding birds have explicitly noted that inclusive fitness returns from alloparenting may accrue, in part, from elevating the survival and subsequent reproduction of the assisted parents. This "load-lightening" hypothesis has a long history and substantial empirical support in certain species (51,52). To the best of our knowledge, however, even in the bird literature, analyses of load-lightening and its effects have never incorporated the additional element of future nepotistic investments in the common kin of parents and their helpers (items 5-8 in Table 2). ...
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Significance Parents raising children rely heavily on related helpers (“alloparents”), who are mainly the mother’s kin rather than the father’s. This “matrilateral bias” is cross-culturally ubiquitous and requires explanation. The dominant evolutionary view is that it serves as a defense against investing resources in unrelated children whose paternity has been misattributed. The evolutionary model proposed here includes paternity uncertainty as one component of the explanation, but adds additional elements derived from the insight that alloparenting constitutes an investment in the mother as well as in her children, raising her subsequent capacity to invest in other relatives. This model lays a foundation for future research on how the receipt of alloparental help changes the lives of mothers.
... g disperse, but many remain in the vicinity of their natal site and subsequently have the opportunity to help at the nests of relatives when their own nests fail, which they often do ( Chapter 3 ). Helping in this species is compensated by future indirect fi tness benefi ts that arise when helpers lighten the workload of male relatives they assist (Meade et al . 2010 ). Last but not least, a signifi cant fraction of acorn woodpeckers inheriting their natal territory do so after dispersing and attempting to breed elsewhere ( Chapter 13 ). In all three of these cases, opportunities to help are provided by remaining in close proximity to kin, and thus further exploration of the selective factors, both ...
... That is, the results of studies investigating changes in feeding behaviour when provisioning activities of caregivers are altered are typically interpreted as being due to concomitant changes in nestling need. When an individual reduces its feeding rate, it results in increased nestling need and compensatory feeding by other group members; conversely, increases in feeding rate by an individual lead to decreased nestling need and 'load lightening' or reduced provisioning by other group members (Canestrari, Marcos, & Baglione, 2007;Hatchwell, 1999;Koenig & Walters, 2012;Meade, Nam, Beckerman, & Hatchwell, 2010). In contrast, there have been relatively fewer studies investigating how or whether caregivers respond to the feeding behaviour of other provisioners independent of their effect on nestling need (Liebl, Browning, & Russell, 2016). ...
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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.
... In some cases, breeders may reduce their investment in young, facilitated by the presence of helpers, a behaviour known as load lightening (Crick, 1992;Johnstone, 2011;Meade, Nam, Beckerman, & Hatchwell, 2010). Load-lightening behaviour can have a positive effect on parental survival and condition by reducing the cost of parental care without young receiving less care overall (Allain e, Brondex, Graziani, & Coulon, 2000;Cockburn et al., 2008;Woxvold & Magrath, 2005). ...
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While most current predictive models agree that the climate is changing, it is not yet clear what impact these changes will have on animal populations. It is vital to determine the potential consequences in order to develop future management and conservation strategies. Climate change may impact population stability by prompting changes in breeding behaviour. For example, if above-average temperatures negatively affect adult body condition, this will increase the cost of parental care. Theory suggests that under this scenario, individuals may trade off their own body condition and survival against that of their young. Despite convincing evidence that this parental care trade-off exists in nature, the potential impact of climate change on parental investment strategies has rarely been investigated. In cooperatively breeding species, group-living adults can gain group size benefits, such as assistance with raising young. These benefits may mediate the effects of climate change on adult condition and subsequent investment in young. Here, we investigated the extent to which high temperatures and rainfall variation affect (1) adult provisioning rates to dependent nestlings, (2) offspring development and (3) the cost of offspring care in the cooperatively breeding pied babbler, Turdoides bicolor. We found that overall, adults provisioned young significantly less on hot days. However, this pattern was affected by rank: dominant individuals provisioned significantly less while subordinates did not. Offspring development was negatively affected by heatwave events, suggesting that young suffer from reduced investment on hot days. However, there was no evidence that the cost of provisioning young increased during heatwave periods, perhaps owing to the reduction in investment by adults. This study provides some of the first evidence that higher temperatures affect investment decisions in cooperative breeders and that dominant and subordinate individuals respond differently to this stressor.
... Cooperatively breeding species, where more than two individuals help care for the young raised from a single brood (reviewed in Koenig and Dickinson 2004;Cockburn 2013;Riehl 2013), may be particularly sensitive to Allee effects (Courchamp et al. 1999b;Somers et al. 2008). This is because in cooperatively breeding species, and particularly in obligate cooperative breeders, individual survival and reproduction are strongly affected by group size, with larger groups providing increased benefits to individuals such as lower costs of parental care (Ridley and Raihani 2007;Russell et al. 2007;Cockburn et al. 2008;Meade et al. 2010), increased predator vigilance (Beauchamp 2008;Bell et al. 2009;Sorato et al. 2012;Ridley et al. 2013), better access to food resources (Kokko et al. 2001) and better access to dispersal opportunities (Ridley 2012). A group that decreases in size may, therefore, be more likely to suffer a further decrease, or even become extinct (Courchamp et al. 1999b;Angulo et al. 2013). ...
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In population dynamics, inverse density dependence can be manifested by individual fitness traits (component Allee effects), and population-level traits (demographic Allee effects). Cooperatively breeding species are an excellent model for investigating the relative importance of Allee effects, because there is a disproportionately larger benefit to an individual of being part of a large group. As a consequence, larger groups have greater performance than small groups, known as the group Allee effect. Although small populations of cooperative breeders may be prone to all levels of Allee effects, empirical evidence for the existence of a demographic Allee effects is scarce. To determine the extent to which Allee effects are present in a cooperatively breeding species, we used a comprehensive 35-year life history database for cooperatively breeding Arabian babblers (Turdoides squamiceps). Firstly, we confirmed the existence of a component Allee effect by showing that breeding individuals in large groups receive greater benefits than those in small groups; second, we confirmed the existence of group Allee effect by showing that larger groups survive longer. And thirdly, we identified a demographic Allee effect by showing that per capita population growth rate is positively affected by population density. Finally, we found that emigration and immigration rates, although dependent on group size, do not buffer against component and group-level Allee effects becoming a demographic Allee effect. Our finding of the existence of all three levels of Allee effects in a cooperative breeder may have important implications for future research and conservation decisions.
... In other bird species, the presence of helpers can increase breeding success and parental survival while increasing helpers' inclusive fitness (Langen 2000, Doerr and Doerr 2007, Russell et al. 2007, Meade et al. 2010. Young may be compelled to stay and help with nesting when natal territories are resource rich (Koenig et al. 1992, Dickinson and McGowan 2005, Baglione et al. 2006. ...
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The Sapayoa (Sapayoa aenigma), a low-density resident of Choco ́ rainforests from Panama to Ecuador, has long perplexed ornithologists. It was originally described as a manakin (Pipridae), but molecular work has revealed its closest living relatives to be Old World suboscines (Eurylaimides) and supported its placement in the monotypic family of Sapayoidae. Despite such phylogenetic intrigue, little is known about the Sapayoa’s general life history or reproductive biology; only one nest has been described. We present information on 2 actively attended and 13 inactive Sapayoa nests in Darie ́n National Park, Panama. We provide the first detailed description of individual effort at an active nest, family group dynamics during the nesting period, the plumage of immature birds, and the range of vocalizations produced. We also present the first documentation of cooperative breeding and compile several recent nesting observations, extending the published Sapayoa breeding period by several months. Furthermore, we describe unusual behaviors among provisioning birds, including mounting between individuals of the same sex and mounting of a female by immature male helpers during chick provisioning. The receiving individual gave a conspicuous solicitation display before each mounting. Finally, we highlight elements of the Sapayoa’s natural history that echo its Old World relatives and contrast with members of the New World Tyranni. For example, the Sapayoa resembles the eurylaimid broadbills—and differs starkly from the manakins—in diet, nest structure, breeding system, and mode of parental care.
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In cooperatively breeding species, helpers take higher risks of getting lower return of investment than breeders due to the incongruity between helping and breeding. Helpers can deal with the risk by curtailing their investment or, if possible, claiming immediate rewards in the cooperation. Given breeders may rely largely on the aid of helpers to raise their offspring, it can be hypothesized that helpers are more likely to make adaptive responses to the incongruity-associated risk in adverse habitats than in good ones. This hypothesis was tested in the giant babax (Babax waddelli) by comparing helpers’ provisioning behaviors between two breeding populations in adverse high-altitude and good low-altitude environments. These two populations differed significantly in their egg size and nestlings’ growth patterns. Helpers in both populations made great contributions to the raising of offspring. During provisioning, helpers in the high-altitude population exhibited significantly higher feeding rates but delivered fewer insects per feeding bout than their counterparts in the low-altitude population. Helpers in both populations displayed a cheating strategy of “non-feeding” to reduce investment in provisioning. They pursued immediate excess rewards via kleptoparasitism of nestling fecal sacs in the high-altitude population but not in the low-altitude one. Accordingly, breeders made different antagonistic actions toward the cheating helpers between populations. Our findings confirm that helpers are prone to deceiving cooperation under poor breeding conditions, and that breeders’ tolerance of the cheating behavior of helpers is determined by their dependence on the helpers’ aid. Significance statement Giant babax is an obligated cooperatively breeding bird that breeds on the Tibetan Plateau. We found that helpers displayed cheating behaviors while they provisioned the brood. Although helpers in both high- and low-altitude populations adopt “non-feeding” strategy to reduce investment in the provisioning, they were more likely to perform contested kleptoparasitism to access the fecal sacs of nestling in the high-altitude population than in the low-altitude one. Our findings suggest that helpers in adverse high-altitude habitats are probable to claim immediate excess reward via cheating strategies.
Chapter
Cooperative breeders are species in which individuals beyond a pair assist in the production of young in a single brood or litter. Although relatively rare, cooperative breeding is widespread taxonomically and continues to pose challenges to our understanding of the evolution of cooperation and altruistic behavior. Bringing together long-term studies of cooperatively breeding birds, mammals, and fishes, this volume provides a synthesis of current studies in the field. The chapters are organised by individual studies of particular species or (in the case of mole-rats) two closely related cooperatively breeding species. Each focuses not only on describing behavior and ecology but also on testing evolutionary hypotheses for the form and function of the diverse and extraordinary cooperative breeding lifestyles that have been discovered. This unique and comprehensive text will be of interest to graduate students and researchers of behavioral ecology and the evolution of cooperation.
Chapter
Cooperative breeders are species in which individuals beyond a pair assist in the production of young in a single brood or litter. Although relatively rare, cooperative breeding is widespread taxonomically and continues to pose challenges to our understanding of the evolution of cooperation and altruistic behavior. Bringing together long-term studies of cooperatively breeding birds, mammals, and fishes, this volume provides a synthesis of current studies in the field. The chapters are organised by individual studies of particular species or (in the case of mole-rats) two closely related cooperatively breeding species. Each focuses not only on describing behavior and ecology but also on testing evolutionary hypotheses for the form and function of the diverse and extraordinary cooperative breeding lifestyles that have been discovered. This unique and comprehensive text will be of interest to graduate students and researchers of behavioral ecology and the evolution of cooperation.
Chapter
Cooperative breeders are species in which individuals beyond a pair assist in the production of young in a single brood or litter. Although relatively rare, cooperative breeding is widespread taxonomically and continues to pose challenges to our understanding of the evolution of cooperation and altruistic behavior. Bringing together long-term studies of cooperatively breeding birds, mammals, and fishes, this volume provides a synthesis of current studies in the field. The chapters are organised by individual studies of particular species or (in the case of mole-rats) two closely related cooperatively breeding species. Each focuses not only on describing behavior and ecology but also on testing evolutionary hypotheses for the form and function of the diverse and extraordinary cooperative breeding lifestyles that have been discovered. This unique and comprehensive text will be of interest to graduate students and researchers of behavioral ecology and the evolution of cooperation.
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1. Alloparental care in cooperatively‐breeding species may alter breeder age‐specific survival and reproduction, and subsequently senescence. The helping behaviour itself might also undergo age‐related change, and decisions to help in facultative cooperative breeders are likely to be affected by individual condition. 2. Helpers in long‐tailed tits (Aegithalos caudatus) assist relatives after failing to raise their own brood, with offspring from helped nests being more likely to recruit into the breeding population. 3. Using data collected over 25 years, we examined the age‐trajectories of survival and reproduction in adult long‐tailed tits to determine how these were affected by the presence or absence of helpers, and how helper behaviour changed with age. 4. There was evidence for increased reproductive performance with breeder age, but no effect of age on the probability of survival. We found no evidence of significant senescent decline in survival or reproductive performance, although individuals accrued less inclusive fitness in their last year of life. Lifetime reproductive success was positively related to both reproductive lifespan and body mass. Within a season, breeders that were assisted by helpers enjoyed greater reproductive success through enhanced offspring recruitment in the following year. We found no evidence that age affected an individual’s propensity to help, or the amount of indirect fitness accrued through helping. 5. We found a positive correlation between lifespan and multiple components of reproductive success, suggesting that individual variation in quality underpins age‐related variation in fitness in this species. Helping decisions are driven by condition, and lifetime inclusive fitness of immigrants was predicted by body mass. These findings further support individual heterogeneity in quality being a major driver for fitness gains across the life course of long‐tailed tits.
Article
In species with biparental and cooperative brood care, multiple carers cooperate by contributing costly investment to raise a shared brood. However, shared benefits and individual costs also give rise to conflict among carers over investment. Coordination of provisioning visits has been hypothesized to facilitate the resolution of this conflict, preventing exploitation, and ensuring collective investment in the shared brood. We used a 26-year study of long-tailed tits, Aegithalos caudatus, a facultative cooperative breeder, to investigate whether care by parents and helpers is coordinated, whether there are consistent differences in coordination between individuals and reproductive roles, and whether coordination varies with helper relatedness to breeders. Coordination takes the form of turn-taking (alternation) or feeding within a short time interval of another carer (synchrony), and both behaviors were observed to occur more than expected by chance, i.e. ‘active’ coordination. First, we found that active alternation decreased with group size while active synchrony occurred at all group sizes. Secondly, we show that alternation was repeatable between observations at the same nest, while synchrony was repeatable between observations of the same individual. Active synchrony varied with reproductive status, with helpers synchronizing visits more than breeders, although active alternation did not vary with reproductive status. Finally, we found no significant effect of relatedness on either alternation or synchrony exhibited by helpers. In conclusion, we demonstrate active coordination of provisioning by carers and conclude that coordination is a socially plastic behavior depending on reproductive status and the number of carers raising the brood.
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In cooperatively breeding species, helper aid may affect dominant breeders’ investment trade-offs between current and future reproduction. By compensating for the care provided by helpers, breeders can reduce the costs of reproduction and improve chances of survival. Also, helper care can be additive to that of dominants, resulting in higher success of the current brood. However, the influence of helpers on offspring care itself may be the by-product of group size and territory quality. Therefore to make conclusive inferences about causation of additive and compensatory care as a result of help per se requires disentangling the impact of helping from other factors determining parental investment. In this study, we use 20 years of offspring provisioning data to investigate the effect of helping on breeder and overall offspring provisioning rates in the facultative cooperatively breeding Seychelles warbler ( Acrocephalus sechellensis ). Our extensive dataset allowed us to effectively control for the effects of living in a larger group and in territories with higher food availability. We show compensatory and additive care in response to helper aid. Helpers lightened the provisioning load of the dominant male and female and increased the total provisioning to the nestlings. This was irrespective of group size or territory quality (food availability). Our results illustrate how multiple benefits of helping behaviour can simultaneously be fundamental to the evolutionary maintenance of cooperative behaviour.
Chapter
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Cooperative breeders are species in which individuals beyond a pair assist in the production of young in a single brood or litter. Although relatively rare, cooperative breeding is widespread taxonomically and continues to pose challenges to our understanding of the evolution of cooperation and altruistic behavior. Bringing together long-term studies of cooperatively breeding birds, mammals, and fishes, this volume provides a synthesis of current studies in the field. The chapters are organised by individual studies of particular species or (in the case of mole-rats) two closely related cooperatively breeding species. Each focuses not only on describing behavior and ecology but also on testing evolutionary hypotheses for the form and function of the diverse and extraordinary cooperative breeding lifestyles that have been discovered. This unique and comprehensive text will be of interest to graduate students and researchers of behavioral ecology and the evolution of cooperation.
Chapter
Cooperative breeders are species in which individuals beyond a pair assist in the production of young in a single brood or litter. Although relatively rare, cooperative breeding is widespread taxonomically and continues to pose challenges to our understanding of the evolution of cooperation and altruistic behavior. Bringing together long-term studies of cooperatively breeding birds, mammals, and fishes, this volume provides a synthesis of current studies in the field. The chapters are organised by individual studies of particular species or (in the case of mole-rats) two closely related cooperatively breeding species. Each focuses not only on describing behavior and ecology but also on testing evolutionary hypotheses for the form and function of the diverse and extraordinary cooperative breeding lifestyles that have been discovered. This unique and comprehensive text will be of interest to graduate students and researchers of behavioral ecology and the evolution of cooperation.
Chapter
Cooperative breeders are species in which individuals beyond a pair assist in the production of young in a single brood or litter. Although relatively rare, cooperative breeding is widespread taxonomically and continues to pose challenges to our understanding of the evolution of cooperation and altruistic behavior. Bringing together long-term studies of cooperatively breeding birds, mammals, and fishes, this volume provides a synthesis of current studies in the field. The chapters are organised by individual studies of particular species or (in the case of mole-rats) two closely related cooperatively breeding species. Each focuses not only on describing behavior and ecology but also on testing evolutionary hypotheses for the form and function of the diverse and extraordinary cooperative breeding lifestyles that have been discovered. This unique and comprehensive text will be of interest to graduate students and researchers of behavioral ecology and the evolution of cooperation.
Chapter
Full-text available
Cooperative breeders are species in which individuals beyond a pair assist in the production of young in a single brood or litter. Although relatively rare, cooperative breeding is widespread taxonomically and continues to pose challenges to our understanding of the evolution of cooperation and altruistic behavior. Bringing together long-term studies of cooperatively breeding birds, mammals, and fishes, this volume provides a synthesis of current studies in the field. The chapters are organised by individual studies of particular species or (in the case of mole-rats) two closely related cooperatively breeding species. Each focuses not only on describing behavior and ecology but also on testing evolutionary hypotheses for the form and function of the diverse and extraordinary cooperative breeding lifestyles that have been discovered. This unique and comprehensive text will be of interest to graduate students and researchers of behavioral ecology and the evolution of cooperation.
Chapter
Cooperative breeders are species in which individuals beyond a pair assist in the production of young in a single brood or litter. Although relatively rare, cooperative breeding is widespread taxonomically and continues to pose challenges to our understanding of the evolution of cooperation and altruistic behavior. Bringing together long-term studies of cooperatively breeding birds, mammals, and fishes, this volume provides a synthesis of current studies in the field. The chapters are organised by individual studies of particular species or (in the case of mole-rats) two closely related cooperatively breeding species. Each focuses not only on describing behavior and ecology but also on testing evolutionary hypotheses for the form and function of the diverse and extraordinary cooperative breeding lifestyles that have been discovered. This unique and comprehensive text will be of interest to graduate students and researchers of behavioral ecology and the evolution of cooperation.
Chapter
From an evolutionary point of view, cooperative breeding and brood parasitism seem to have little in common. In avian cooperative species, individuals help feed young that are not their offspring, whereas brood parasites exploit the parental behaviour of a host, thus avoiding the costs of raising their progeny. Recent evidence, however, uncovered an evolutionary link between the two systems. On the one hand, it has been shown theoretically and empirically that conspecific brood parasitism (CBP) and cooperative breeding can be extremes of a continuum of parental care, where kinship among interacting females and ecological constraints on independent reproduction shape individual decisions. On the other hand, cooperative breeding and interspecific brood parasitism (IBP) might co-evolve, because the benefits of extra-care may select for a preference of nests with helpers in parasites, whereas a defensive function of helpers against the parasites would promote cooperative breeding in hosts. According to this hypothesis, the richness of cooperative species and brood parasites worldwide shows striking similarities, and within the two major host spots (Australasia and sub-Saharan Africa), passerine species that host obligate brood parasites are more likely to breed cooperatively. Although we have just begun to unravel the link between cooperative breeding and brood parasitism, the results have already widened our perspective on the evolution of avian breeding systems. Future studies that aim at building this bridge should therefore be encouraged.
Article
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Parental investment affects the future survival and reproductive success of breeders. Therefore, breeders should optimize the amount of care they invest into the current offspring. In cooperative breeding systems, the amount of breeders' parental care is influenced by the behavior of brood-care helpers. Such workload adjustment is expected to depend on the task that needs to be fulfilled. While investment rules of breeders in respect to single tasks are well investigated in many bird and mammal species, little is known about behavioral adjustment of breeders when dealing with multiple tasks. Here, we examined the workload adjustment in multiple tasks of female breeders in the cooperatively breeding fish Neolamprologus obscurus. By combining behavioral observations with helper removal experiments in a wild population, we show that female territory defense and offspring care significantly decreased with increasing helper number. Furthermore, the workload invested in these tasks significantly increased after the removal of a helper, suggesting load-lightening effects in territory defense and offspring care. On the other hand, female territory maintenance behavior (i.e., excavating sand from the breeding shelter) did not correlate with helper number. While sand excavation significantly increased after the helper removal experiment, the size of the excavated stone area decreased after the helper removal in the recent study, suggesting that sand excavation may have additive effects for the breeders. These results demonstrate and underline the importance of task-dependent workload adjustment in cooperative breeders.
Chapter
The evolution of cooperation has been a focus of interest for evolutionary biologists for over a hundred years (Darwin 1859; Kropotkin 1908; Williams 1966). While all forms of cooperation challenge the centrality of competition in the process of evolution, cooperative and eusocial breeding systems, where offspring produced by a small number of breeding individuals are reared by nonbreeding helpers or workers, raise some of the most fundamental questions about the level at which selection operates the measurement of....
Chapter
Full-text available
Cooperative breeders are species in which individuals beyond a pair assist in the production of young in a single brood or litter. Although relatively rare, cooperative breeding is widespread taxonomically and continues to pose challenges to our understanding of the evolution of cooperation and altruistic behavior. Bringing together long-term studies of cooperatively breeding birds, mammals, and fishes, this volume provides a synthesis of current studies in the field. The chapters are organised by individual studies of particular species or (in the case of mole-rats) two closely related cooperatively breeding species. Each focuses not only on describing behavior and ecology but also on testing evolutionary hypotheses for the form and function of the diverse and extraordinary cooperative breeding lifestyles that have been discovered. This unique and comprehensive text will be of interest to graduate students and researchers of behavioral ecology and the evolution of cooperation.
Chapter
Cooperative breeders are species in which individuals beyond a pair assist in the production of young in a single brood or litter. Although relatively rare, cooperative breeding is widespread taxonomically and continues to pose challenges to our understanding of the evolution of cooperation and altruistic behavior. Bringing together long-term studies of cooperatively breeding birds, mammals, and fishes, this volume provides a synthesis of current studies in the field. The chapters are organised by individual studies of particular species or (in the case of mole-rats) two closely related cooperatively breeding species. Each focuses not only on describing behavior and ecology but also on testing evolutionary hypotheses for the form and function of the diverse and extraordinary cooperative breeding lifestyles that have been discovered. This unique and comprehensive text will be of interest to graduate students and researchers of behavioral ecology and the evolution of cooperation.
Article
Despite its importance for the evolution of cooperative breeding, it has proven difficult to determine whether helpers improve their recipients’ fitness. Helpers affect fitness in multiple ways, both positive and negative, but their effects can also be concealed through reduced maternal investment. Furthermore, determining the direction of causation is difficult, as helper presence may indicate a productive territory, rather than high productivity indicating an effect of help. In cooperatively breeding red-winged fairy-wrens (Malurus elegans) groups reduce care when they have male helpers, but groups with female helpers do not, so nestlings receive more food. Thus our predictions vary with helper sex rather than helper number, and by studying within-group changes with regard to group composition we separate phenotypically plastic responses from among-group correlations. Females did not reduce egg size in response to an increasing number of female helpers. However, more male or female helpers allowed females to lay larger clutches and more female helpers reduced re-nesting intervals. There was mixed support for a benefit of load lightening: Helpers, but not breeders, gained survival benefits with increasing number of male helpers. However, helper survival decreased with the number of female helpers, suggesting that increased competition counterbalanced these male helper benefits. We also found consistent among-group differences, which would have erroneously been interpreted as helper effects had we not disentangled the within-group changes with regard to group composition. This study highlights the importance of assessing carers’ benefits in relation to both group composition and size, and of investigating the within-individual plastic response of helper effects.
Chapter
Full-text available
Cooperative breeders are species in which individuals beyond a pair assist in the production of young in a single brood or litter. Although relatively rare, cooperative breeding is widespread taxonomically and continues to pose challenges to our understanding of the evolution of cooperation and altruistic behavior. Bringing together long-term studies of cooperatively breeding birds, mammals, and fishes, this volume provides a synthesis of current studies in the field. The chapters are organised by individual studies of particular species or (in the case of mole-rats) two closely related cooperatively breeding species. Each focuses not only on describing behavior and ecology but also on testing evolutionary hypotheses for the form and function of the diverse and extraordinary cooperative breeding lifestyles that have been discovered. This unique and comprehensive text will be of interest to graduate students and researchers of behavioral ecology and the evolution of cooperation.
Article
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The incubation period of Long-tailed Tits Aegithalos caudatus is highly variable, ranging from 14 to 21 days. Females alone incubate the eggs, but males provide females with some food during the incubation period, although females must also forage for themselves. Our aim was to investigate whether male provisioning of incubating females influenced female incubation behavior and the length of the incubation period. Provisioning rates varied between males, and female nest attentiveness was negatively related to short-term variation in the rate at which their partner fed them. However, the provisioning rate of individual males also varied significantly through time, and there was no significant effect of male care on female incubation across the whole incubation period. There was no evidence that variation in the behavior of either males or females influenced the length of the incubation period
Article
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We determined whether nest-site characteristics influence reproductive success and whether experience influences nest-site selection in a population of cooperatively breeding Long-tailed Tits (Aegithalos caudatus). Nest predation was high; only 17% of breeding attempts resulted in fledged young. The height of nests was an important determinant of success; low nests were significantly more successful than high nests. A breeder's age, natal nest site, and breeding experience had no significant effect on nest-site selection. However, failed breeders who helped at the successful nests of conspecifics built subsequent nests lower than nests built prior to their helping experience. Failed breeders who did not help showed no reduction in the height of subsequent nests. Moreover, the subsequent reproductive success of failed breeders who helped was significantly higher than that of failed breeders who did not help. We conclude that helpers gain information on nest-site quality through their helping experience and thus gain a direct fitness benefit from their cooperative behavior. We suggest that experience as a helper offers a more reliable cue to nest-site quality than breeding experience because helpers are associated with nests only during the nestling phase when few nests are depredated. In contrast, although successful breeders may experience success with a low nest, they are even more likely to have experienced the failure of low nests because of the high rate of nest predation.
Article
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In approximately 3.2% of bird species individuals regularly forgo the opportunity to breed independently and instead bree cooperatively with other conspecifics, either as non–reproductive ‘helpers’ or as co–breeders. The traditional explanatio for cooperative breeding is that the opportunities for breeding independently are limited owing to peculiar features of th specie's breeding ecology. However, it has proved remarkably difficult to find any common ecological correlates of cooperativ breeding in birds. This difficulty has led to the ‘life history hypothesis’, which suggests that the common feature of cooperativel breeding birds is their great longevity, rather than any particular feature of their breeding ecology. Here, we use a comparativ method to test the life history hypothesis by looking for correlations between life history variation and variation in th frequency of cooperative breeding. First, we find that cooperative breeding in birds is not randomly distributed, but concentrate in certain families, thus supporting the idea that there may be a common basis to cooperative breeding in birds. Second, increase in the level of cooperative breeding are strongly associated with decreases in annual adult mortality and modal clutch size. Third, the proportion of cooperatively breeding species per family is correlated with a low family–typical value of annua mortality, suggesting that low mortality predisposes cooperative breeding rather than vice versa. Finally, the low rate o mortality typically found in cooperatively breeding species is associated with increasing sedentariness, lower latitudes and decreased environmental fluctuation. We suggest that low annual mortality is the key factor that predisposes avian lineage to cooperative breeding, then ecological changes, such as becoming sedentary, further slow population turnover and reduc opportunities for independent breeding. As the traditional explanation suggests, the breeding habitat of cooperatively breedin species is saturated, but this saturation is not owing to any peculiar feature of the breeding ecology of cooperative breeders. Rather, the saturation arises because the local population turnover in these species is unusually slow, as predicted by th life history hypothesis.
Article
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In a population of long-tailed tits Aegithalos caudatus all birds attempted to breed monogamously, but some helped to provision the nestlings of another pair if their own breeding attempt failed. An individual's investment rules will determine the fitness consequences of helping for breeders and helpers, and the aim of this study was to examine how individual investment varied with the number of carers. Provisioning behaviour was investigated in two ways. First, observations of natural variation showed that males and females reduced their provisioning effort when aided by one helper, but showed no further reduction with additional helpers. By contrast, helpers did not adjust their provisioning effort in relation to the number of helpers at a nest. Secondly, the reaction of parents to the presence of helpers was tested experimentally by the temporary removal of helpers. Both parents significantly increased their provisioning rate when helpers were absent, and the total provisioning rate was unaffected by the manipulation. The reactions of breeders and helpers to the number of carers, and the fitness benefits for breeders and helpers are discussed.
Article
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Male parental care is rare in most groups of animals but common in birds. Among birds considerable variation exists in the form of care provided their young; recent developments in several areas may help to explain this variation. These include (i) improvements in the comparative method, particularly the use of phylogenies to investigate questions about the evolution (origin) of behavior; (ii) field studies designed to determine the fitness benefits of care and the selective factors that maintain it; and (iii) investigations of the mechanisms of care, especially its neural and hormonal bases. The greatest challenge to functional explanations of male care has come from the revelation that males frequently provide care for offspring that are not genetically their own. Resolving this apparent paradox will require more accurate accounting of the costs and the benefits of care, and greater attention to the form of care provided by males. Data support the following working hypothesis: In taxa in which males incubate, as opposed to providing other forms of care, sexual selection may be less intense and males may resemble females more in appearance and physiology. Males may also be more likely to be the genetic sires of the offspring they care for, perhaps because of the greater cost to females of multiple matings or perhaps because male incubation is incompatible with sustained sexual behavior. Ultimately, an integrated consideration of history, function, mechanism, and development should reveal the interplay of factors that have led to male parental care in birds and that account for its maintenance in various forms today.
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(1) Brood reductions and enlargements were carried out in kestrel nests to evaluate the consequences of raising different numbers of nestlings for both the offspring and the parents. (2) Brood enlargements caused increased daily hunting activity of the parents, reduced growth rate of the nestlings, increased nestling mortality and enhanced weight loss in the female parent. Brood reductions caused an increased food intake by the nestlings, in spite of (non-significantly) reduced parental hunting activity. Local survival of the parents was negatively correlated with the experimental change in brood size. (3) A review of the literature on brood enlargements is presented, showing that parents were able to raise more young till fledging than their natural broods in twenty-nine out of forty altricial bird species investigated. Negative effects of brood enlargements on parental survival or future reproduction were established in eight out of twelve species investigated. (4) The results are consistent with the theory that parental work for the offspring entails an inherent reduction in future reproductive output and that natural broods, by being smaller than the maximum number of nestlings that can be raised, maximize the total reproductive output.
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Conducted 25 removal experiments in which superb fairy-wren philopatric male helpers were removed from their nests and held captive for 24 hrs. Upon each S's return, the reunion had 1 of 2 outcomes: The S was either accepted passively back into his group by the dominant male, or he was subjected to extreme harassment by the male before being accepted back the next day. Removals during the nonbreeding season never resulted in aggression; removals during fertilization and incubation resulted in aggression 50% of the time; and removals during the nestling/fledgling stage resulted in aggression 83% of the time. It is suggested that helpers provide help to dominant males in order to avoid expulsion. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
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Summary 1. Long-tailed tits ( Aegithalos caudatus ) are a cooperatively breeding species in which helpers often invest effort in the provisioning of young that are not their own. 2. We quantified the lifetime reproductive success (LRS) and the individual fitness, lambda, of 228 long-tailed tits using 8 years of field data. Calculation of lambda took account of the effect of helpers on reproductive success, and thus lambda estimates the inclusive fitness of individuals. We examined the relationships between the fitness esti- mators and the provisioning effort, cohort, body size and dispersal status of individuals. 3. LRS of individuals which bred successfully varied between 0 and 13 local recruits (mean 0·71 ± 0·11 SE); lambda varied between 0 and 2·54 (mean 0·28 ± 0·04). The meas- ures were highly correlated, and their distributions were strongly skewed. Helping by individuals contributed little to their fitness, but one-fifth of birds that accrued fitness did so only through helping. In general, individuals that gained fitness from helping did not gain fitness directly. 4. Both LRS and individual fitness were significant predictors of the number of grand- offspring that an individual had, but they accounted for only about one-third of the variation. 5. When variance in LRS was partitioned between length of breeding life span, average fecundity and offspring survival, the latter component was the most important in accounting for variance in LRS. 6. Offspring local survival was positively related to the provisioning effort of mothers, but was unrelated to that of fathers. As a result, the fitness of females was positively related to their provisioning effort. 7. Immigrant birds tended to be more reproductively successful than philopatric ones. Among females, only immigrant birds accrued any LRS or individual fitness. 8. The probability that an individual had at least one offspring recruit to the local breeding population varied among cohorts, probably as a result of variation among years in off- spring local survival. This resulted in variation among cohorts in the individual fitness of females, but not in their LRS, nor in the LRS or individual fitness of males.
Article
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Summary • In the cooperative breeding system of the long-tailed tit Aegithalos caudatus failed breeders may become helpers at the nest of another pair to whom they are usually related. The aim of this study was to determine the effect of helping behaviour on the survival of helpers and the recipients of their help. • We used capture–mark–recapture data and the MARK program to analyse survival of 482 birds ringed as fledglings and 155 birds ringed as adults. • Juvenile males had a higher survival probability than juvenile females across all years whilst their subsequent adult survival was constant. Within sex, the survival probability of juveniles that fledged from nests with helpers was higher than those that did not receive help as nestlings. • Failed breeders that became helpers had a higher survival probability (56%) than those failed breeders that did not become helpers (46%). Successful breeders had a survival probability of 56% regardless of whether they received help or not. • Failed breeders that became helpers had a lower probability of successfully breeding in a subsequent year (27%) when compared to those failed breeders that did not become helpers (38%). •6. We conclude that helpers gain kin-selected fitness benefits through the increased survival of related offspring but not through the increased survival of related breeders. Furthermore, helpers gain direct fitness benefits through increased personal survival, but at a cost of reduced probability of successful future personal reproduction.
Article
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Cooperative breeding, where some individuals help to raise offspring that are not their own, is a relatively rare social system in birds. We studied the breeding biology of a declining cooperative breeder, the grey-crowned babbler Pomatostomus temporalis, with the aim of isolating the social factors that affect its reproductive success. Most breeding pairs were assisted by philopatric offspring, although pairs could breed successfully without helpers. Females laid up to four clutches (usually three eggs per clutch) per season. Male (but not female) helpers increased the number of young fledged from individual nests and the likelihood of re-nesting, resulting in higher seasonal fledgling production. Helper effects on brood size and fledgling production were greater in the second year of the study, which was also characterized by higher nest failure. This suggests that helpers enhance reproduction more in poor conditions. Our study demonstrates the interacting effects of social and ecological factors on reproductive success, and that retention of offspring is not always beneficial for the breeders in cooperative species.
Article
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Summary 1. Long-tailed tits Aegithalos caudatus L. are cooperative breeders in which breeders that have failed in their own breeding attempt become helpers at the nest of relatives. We investigated the effects of kinship on the spatial dynamics of non-breeding flocks of long-tailed tits in order to determine the information available on the kinship of other members of the population from their use of home ranges. 2. A novel method of home range analysis was devised based on 'convex hull peeling'. This method takes into account the dispersion of all fixes within a home range and per- mits the quantitative analysis of home range use. In addition, the method allows the extent of overlap between adjacent home ranges to be determined and the use of those areas to be investigated. 3. Non-breeding flocks of long-tailed tits were composed mainly of relatives, but also included unrelated immigrants. Flock ranges were large and there was extensive overlap between adjacent flocks. 4. The degree of range overlap was significantly affected by the relatedness of flocks. If two flocks contained close relatives they were more likely to overlap than two flocks containing non-relatives. Moreover, the amount of overlap was significantly greater for two adjacent related flocks than for two adjacent unrelated flocks. 5. The use of overlapping areas of non-breeding ranges of long-tailed tit flocks was also influenced significantly by relatedness. Overlapping flocks that were unrelated to each other usually avoided areas of overlap, while related flocks did not generally show such avoidance behaviour. 6. Kinship has significant effects on the spatial dynamics of non-breeding flocks of long-tailed tits and therefore flock behaviour can provide information on the related- ness of other members of the population that might be important for helping decisions in this cooperatively breeding species.
Chapter
Cooperative breeding is an unusual kind of social behaviour, found in a few hundred species worldwide, in which individuals other than the parents help raise young. Understanding the apparently altruistic behaviour of helpers has provided numerous challenges to evolutionary biologists. This book includes detailed first-hand summaries of many of the major empirical studies of cooperatively breeding birds. It provides comparative information on the demography, social behaviour and behavioural ecology of these unusual species and explores the diversity of ideas and the controversies which have developed in this field. The studies are all long-term and consequently the book summarises some of the most extensive studies of the behaviour of marked individuals ever undertaken. Graduate students and research workers in ornithology, sociobiology, behavioural ecology and evolutionary biology will find much of value in this book.
Chapter
Cooperative breeding is an unusual kind of social behaviour, found in a few hundred species worldwide, in which individuals other than the parents help raise young. Understanding the apparently altruistic behaviour of helpers has provided numerous challenges to evolutionary biologists. This book includes detailed first-hand summaries of many of the major empirical studies of cooperatively breeding birds. It provides comparative information on the demography, social behaviour and behavioural ecology of these unusual species and explores the diversity of ideas and the controversies which have developed in this field. The studies are all long-term and consequently the book summarises some of the most extensive studies of the behaviour of marked individuals ever undertaken. Graduate students and research workers in ornithology, sociobiology, behavioural ecology and evolutionary biology will find much of value in this book.
Article
Helpers at the nest of cooperatively breeding birds often "lighten-the-load' of the breeders, by allowing them to decrease their effort. When the shape of the relationship between survival cost and provisioning effort is concave-up then a helper incurs only a small increment in mortality, for a given amount of help, but the breeder benefits from a larger fall in mortality. A convex-up relationship for pre-breeders may explain why some groups do not breed cooperatively. Load-lightening could provide significant extra gains to the helper's future indirect fitness by increasing the lifespan and life-time reproductive success of related breeders. -Author
Article
Both food availability and size of the group attending the nest had significant effects on Merops bullockoides productivity, while the characteristics of breeders (age, experience) did not. Helpers had their effect almost entirely through increased productivity per nesting attempt, each helper on average increasing the number of fledglings by 0.50 (±0.06 SE). The activities of helpers did not affect either breeder survival or number of nesting attempts per year. Presence of helpers did not affect clutch size, had no influence on the probability of successful hatching, but dramatically increased the rate of provisioning per nestling. As a consequence of their feeding contributions, helpers significantly decreased both the probability of nestling starvation and the degree of nestling developmental retardation due to food stress. More young fledged, and fledged in better condition, from helped nests. The ability of bee-eater helpers to increase fledging success through their feeding contribution is related to the environmentally unpredictable, and often harsh, conditions at Nakuru. Nestling starvation rates were high (48% of all hatchlings), whereas predation losses were low (4% of eggs laid). Presence of one helper effectively doubled the fledging success of an unaided pair; the effect of increasing numbers of helpers was linear across all commonly observed group sizes. Not only should the presence/absence of helpers influence the decision to breed, but breeders are expected to compete for potential helpers. From the perspective of a potential helper, the large indirect fitness benefit obtained by helping close kin makes helping a viable alternative to breeding. Thus, under some circumstances, helping behaviour may be a first-choice option rather than a second-choice alternative adopted because breeding opportunities are constrained. -from Authors
Article
A completely colour-banded population of these small, sociable, multi-brooded passerines of the sub-family Malurinae was studied for more than four years at Gungahlin, Canberra, A.C.T. Their plumage, behaviour, song, breeding biology and population dynamics are discussed with particular reference to the persistence of the young-of-the-year within the family group throughout the winter, the consequent problems of dispersion and, ultimately, the frequent occurrence of more than one mature mule in the breeding group. It is suggested that this apparent polyandry enables the species to be reproductively more successful within the limits of a variable climate.
Article
(1) This paper describes the survival of juvenile blackbirds according to their weight as 8-day-old nestlings. In a 4-year study of 748 individually colour-ringed nestlings, heavy nestlings were more likely to survive to breed in the study area than lighter nestlings. (2) Nestlings below 35 g never survived to fledge; those above 45 g showed a linear increase in the probability of survival to independence, up to heaviest nestlings in the sample; between 35 and 45 g there was a linear, but more rapid, increase in survival prospects with weight. The shape of the relationship between nestling weight and juvenile survival was similar in different years, through the season, and between brood sizes and age ranks within broods. (3) Differential mortality by nestling weight occurred from ringing to fledging, from fledging to 2 weeks after fledging (when the young are still fed by their parents and are easily located on territories), and from 2 weeks to 1 month after fledging (when the young are independent but can be difficult to locate). However, birds that survived this period apparently had a random chance of breeding. (4) These findings on juvenile survival suggest that nestling weight itself influences juvenile survival, not some correlate such as brood size. (5) A knowledge of the shape of the relationship between nestling weight and juvenile survival allows one to measure nestling `quality&apos; as the probability that a nestling will survive to breed. In practice, the probability of survival to shortly after nutritional independence might be an adequate estimate of relative probabilities of recruitment to the breeding population in many bird species.
Article
1. In many species of birds the mean clutch size is not constant through the breeding season. Some species show a seasonal pattern of declining clutch size, while others can show a mid-season peak. We suggest an evolutionary interpretation of the different patterns of seasonal change in birds, and test predictions by analysis of nest-record data held by the British Trust for Ornithology (BTO). 2. We assume that conditions for breeding will show a seasonal pattern of improvement and then decline, and that the optimal clutch size (Lack 1947) is larger for each individual in the population when the conditions for breeding are better. 3. In multi-brooded species, seasonal reproductive success is determined partly by the number of broods that parents can raise during the breeding season, not simply by the success of a single brood. Thus, we suggest that individuals in multi-brooded species should be selected to start breeding before the date when their optimal clutch size is greatest, while single-brooded s
Article
An individual's optimal investment in young depends partly on the number of individuals caring for the same brood. In cooperative breeders, the investment strategy of parents with helpers is variable. When parents maintain the same effort regardless of helper number, helper care is additive. When parents fully compensate for the care of helpers by decreasing their own effort, total care does not increase. A study of long-tailed tits Aegithalos caudatus showed that both parental strategies may occur within a species, depending on the number of helpers. A comparative analysis of 27 cooperative breeders was conducted to test the predictions of a graphical model that care is additive when nestling starvation is frequent and parents exhibit compensatory reductions in care when starvation is rare. Both predictions were supported. In this interspecific comparison, a species' mean group size was not associated with compensatory responses by parents. There was some evidence that males and females had different investment rules. Males tended to show compensatory reductions in care when adult survival rate was low. In contrast, while both sexes showed compensation when nestling starvation was infrequent, this association was significant only for females.
Article
This chapter describes some aspects of research on the cooperative breeding system of the long tailed tit Aegithalos caudatus. The principal aim of the chapter is to bring together evidence from various sources concerning the role of kin selection and ecological constraints in the evolution of cooperative breeding in this species. Many studies of vertebrate cooperative breeding systems have shown that helpers assist relatives in raising their offspring. A major reason for initiating a study on long tailed tits is that their helping behavior is atypical and does not conform to this sequence of events because all helpers are failed breeders that ‘‘redirect’’ their care to become helpers. The ability to discriminate between kin and non kin plays a major role in the evolution of social behavior. The direct fitness benefits of helping are those that enhance the personal reproductive success of helpers. The direct fitness benefits of helping are those that enhance the personal reproductive success of helpers. Helpers may gain indirect fitness benefits either by helping relatives to increase productivity of their current breeding attempt, or by reducing the reproductive costs of related breeders, thereby enhancing their survival. The main conclusions regarding the role of kin selection in the evolution of cooperative breeding in long tailed tits are have been listed out: (1) helpers exhibit a kin preference in helping behavior using a learned vocal kin recognition mechanism, (2) helpers increase the productivity of their relatives by increasing recruitment of fledglings of the helped brood, and (3) the kin selected fitness benefit of helping is the sole source of inclusive fitness for a substantial proportion of individuals.
Article
An overview of the extensive and frequently controversial literature on communally breeding birds developed since the early 1960s, when students of evolution began to examine sociality as a product of natural selection. Jerram Brown provides original data from his own theoretical and empirical studies and summarizes the wide array of results and interpretations made by others.Originally published in 1987.The Princeton Legacy Library uses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These paperback editions preserve the original texts of these important books while presenting them in durable paperback editions. The goal of the Princeton Legacy Library is to vastly increase access to the rich scholarly heritage found in the thousands of books published by Princeton University Press since its founding in 1905.
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Presents data from a 12-yr study of the reproductive success of more than 1,000 red deer on the island of Rhum, Scotland in which the contrasting factors affecting reproductive success in males and females are shown to be the ultimate cause of most differences between the sexes. Competition between stags for harems is intense and males fight regularly for possession. The hind's breeding success is related to the number of offspring the hind can produce and rear, and depends mainly on the food resources available to her. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
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Summary • We examined the influence of helpers on reproductive success in the apostlebird using data gathered over three breeding seasons (116 nests, 34 breeding groups). Initially, annual productivity and individual components of reproductive success were examined in relation to group size (two to 17 birds). The effect of helping per se was then examined in a reduced data set by comparing (a) the predictive power of group size and actual helper numbers, and/or (b) the productivity of groups that changed in size between nests or seasons. • Group size was positively and linearly related to annual fledgling production and the number of offspring that survived to the following season. This was attributed to the presence of helpers, as the number of birds that fed nestlings, but not group size, was significantly related to annual fledging success. Neither group size nor helper number influenced fledgling survival over the subsequent winter. • The probability of re-nesting after a successful first brood increased with group size. Among double-brooded groups, the interval between nests was inversely related to group size. • Clutch size increased linearly with group size among groups with two to five birds, but was not related to group size among larger groups. A matched comparison of groups that changed size between years further suggests that clutch size was facultatively adjusted to group size, a phenomenon rarely reported in species with non-breeding helpers. • Hatching success was not related to group size or the number of birds participating in incubation. • The number of birds provisioning the brood was a better predictor of feeding rate per chick than group size, and was significantly and inversely related to the incidence of nestling starvation. However, there was no relationship between group size and fledgling body mass. • Fledging success per brood increased linearly among groups with three to five members. The only case of pair-breeding was unsuccessful, suggesting that this species is one of only a few birds that may be obligately cooperative. • We found no evidence that helpers influenced the likelihood of nest predation, or the probability of group members surviving to the following season. Journal of Animal Ecology (2005) 74, 1039 –1050 doi: 10.1111/j.1365-2656.2005.01001.x
Article
Helpers at the nest of cooperatively breeding birds often ‘lighten-the-load’ of the breeders, by allowing them to decrease their effort. When the shape of the relationship between survival cost and provisioning effort is concave-up then a helper incurs only a small increment in mortality, for a given amount of help, but the breeder benefits from a larger fall in mortality. A convex-up relationship for pre-breeders may explain why some groups (such as larids) do not breed cooperatively. Load-lightening could provide significant extra gains to the helper's future indirect fitness by increasing the lifespan and life-time reproductive success of related breeders.
Article
In some hole nesting passerine species, long-term monitoring data are available for several geographically independent populations. Climate forcing can then be documented and predictions made on the scale of distribution ranges. Several demographic studies of Paridae report dramatic impacts of wintertime climatic factors. However, these studies were undertaken in populations located in the northern parts of the species' ranges. Studies on the survival of Paridae in their southern ranges are necessary in order to assess potential latitudinal variation in climate forcing on survival. Based on monitoring of individual adult blue tits (Parus caeruleus), the effects of climatic factors on annual survival were assessed in three distinct Mediterranean populations. In these regions, climatic conditions in early summer might be expected to have a strong impact because they can be extremely hot and dry and because at this time of year Paridae are subjected to intrinsic constraints that stem from energetically costly postbreeding moult, recovery from reproductive costs, and from population densities inflated by the new cohort of fledglings. The impact of climatic conditions in early summer was, thus, addressed in addition to that prevailing in winter. In order to consider a large number of local climatic variables while limiting statistical power loss, integrative indices of local climate were built using multivariate techniques. In addition, the NAO and three large-scale factors that are closely linked with atmospheric and oceanic circulation in the intertropical zone were considered as potentially influential factors in winter and early summer. Relationships between blue tit survival and indices of local temperature and precipitation in winter and in early summer were detected. Adult survival also correlated with a large-scale tropical index in early summer: rainfall in the Sahel. This is one of the first quantitative indications that fluctuations in summer climatic conditions explain a significant part of the temporal variation in adult survival in unconnected populations of a sedentary European vertebrate. Furthermore, the results support the hypothesis that summertime local climates in Western Europe are closely linked with atmospheric and oceanic circulation in the intertropical zone.
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This paper reports on part of a three-year study into the biological significance of variation in body size of individuals from a single population of Great Tits in Wytham Woods near Oxford, from 1973 to 1976. It is a reasonable hypothesis that the body size of an individual is controlled partly by heredity and partly by environmental factors. Genetical factors by themselves are shown to account for nearly three-quarters of the total observed phenotypic variance of body size. Of the likely environmental factors considered, only the date of hatching (in 1973) and an annual difference in body size are shown to have significant effects. Previous workers have shown that heavier fledglings have a better chance of surviving the immediate post-fledging period than lighter fledglings (e.g., Perrins 1965). It had been postulated that this differential survival rate might be due to variations in the fat reserves of fledglings. However, the data presented here suggest that this hypothesis is unlikely, and that the body size of fledglings has a more significant influence. The aggressive behaviour of fledgling Great Tits towards one another may be the mechanism responsible for this since it is shown that larger fledglings tend to dominate smaller fledglings.