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Summary Kin recognition can enhance inclusive fitness via nepotism and optimal outbreeding. Mechanisms allowing recognition of patrilineal relatives are of particular interest in species in which females mate promiscuously, leading to paternity uncertainty. Humans are known to detect facial similarities between kin in the faces of third parties [ 1–4 ], and there is some evidence for continuity of this ability in nonhuman primates [ 5–7 ]. However, no study has yet shown that this propensity translates into an ability to detect one’s own relatives, one of the key prerequisites for gaining fitness benefits. Here we report a field experiment demonstrating that free-ranging rhesus macaques ( Macaca mulatta ) spontaneously discriminate between facial images of their paternal half-siblings and unrelated individuals, when both animals are unfamiliar to the tested individual. Specifically, subjects systematically biased their inspection time toward nonkin when the animals pictured were of their own sex (potential threats), relative to when they were of the opposite sex (potential mates). Our results provide strong evidence for visual phenotype matching and the first demonstration in any primate that individuals can spontaneously detect their own paternal relatives on the basis of facial cues under natural conditions. [ABSTRACT FROM AUTHOR]

Recent studies in the field of behavioural ecology have revealed intriguing variation in behaviour within single populations. Increasing evidence suggests that individual animals differ in their average level of behaviour displayed across a range of contexts (animal ‘personality’), and in their responsiveness to environmental variation (plasticity), and that these phenomena can be considered complementary aspects of the individual phenotype. How should this complex variation be studied? Here, we outline how central ideas in behavioural ecology and quantitative genetics can be combined within a single framework based on the concept of ‘behavioural reaction norms’. This integrative approach facilitates analysis of phenomena usually studied separately in terms of personality and plasticity, thereby enhancing understanding of their adaptive nature. [Copyright &y& Elsevier]

Cooperative provisioning dynamics between members of a pair in biparental systems has received a lot of attention, both empirically and theoretically. The dynamics of provisioning in cooperatively breeding groups, however, remains poorly understood. Such groups often include unrelated helpers that may have very different provisioning rules from related helpers and parents, since they accrue different types of fitness benefits from helping. The bell miner, Manorina melanophrys, provides an ideal system in which to investigate cooperative provisioning, because substantial levels of care are provided by a number of unrelated helpers per nest. We experimentally increased brood demand via targeted begging playbacks during nest visits of either breeding males or unrelated male helpers. Both types of males used similar behavioural investment rules, significantly increasing food delivery rate during playback relative to control periods. Surprisingly, all other provisioners also increased their visit rates during playbacks, although to a lesser extent. This could only have been in response to the increase in visits by the target individuals, suggesting an additional indirect mechanism by which individuals in this cooperative setting assess brood demand. The resultant overall increase in food delivery during the playback periods caused nestlings to show the expected reduction in their own begging and an increase in body mass gain. It is therefore interesting how similar the evolved provisioning responses are for all types of group member, irrespective of whether such benefits of investment in the brood are derived via kin selection (fathers) or some future direct increase in fitness (helpers). [Copyright &y& Elsevier]

In variable environments variance-sensitive foraging should be replaced by more profitable sampling behaviour whenever the variation in foraging rewards becomes predictable enough to track. We tested this suggestion in groups of wild Siberian jays, Perisoreus infaustus, during prewinter food-hoarding visits to experimental feeders. As predicted, all groups of jays switched to sampling once food items were clumped into ‘patches’ to create reliable patch-based information concerning prey sizes. However, increases in individual foraging success above chance were not achieved according to a simple ‘win-stay lose-shift’ rule of thumb. Instead jays employed a win-and-return-later strategy, returning more often over the experimental session to privately sampled patches containing the four largest of five prey sizes. In contrast, public information that was gained by observing patch sampling by other group members involved a more gradual increase in the probability of patch use with the prey size involved. Use of public versus private information did not differ according to sex or social status. Even though the jays did not achieve the individually optimal strategy in this specific experimental set-up, their sampling behaviour using both public and private information are suggested to maximize both individual and group-wide foraging efficiencies when exploiting the ephemeral food sources typical of boreal taiga forests. [ABSTRACT FROM AUTHOR]

Variance sensitivity theory predicts that optimal foragers should take into account not only the mean but also the variance in rewards offered by alternative foraging options. Whereas a positive energy budget should favor variance aversion, a negative one should favor variance-prone choices. The risk of starvation is the most obvious fitness threshold that can select for variance-prone behavior, but additional thresholds may exist such as the energy required for reproduction. Previous studies of variance sensitivity have often been performed in captivity, and few have demonstrated the predicted state-dependent changes in individual variance preferences. We trained groups of wild Siberian jays (Perisoreus infaustus) to forage from one-shot feeders containing 3 color-coded options differing only in the variance of reward sizes. Not only did we find variance-sensitive behavior under natural conditions but also, for the first time, demonstrate the presence of significant differences in variance sensitivity within groups. Breeders exhibited a preference for high-variance rewards, whereas unrelated subordinates within the same groups preferred low-variance options. These results did not reflect risk of starvation (indexed by body mass) but might be explained by the additional energy needs of breeders compared with subordinates prior to the breeding season. [ABSTRACT FROM AUTHOR]

Offspring begging provides parents with an honest signal of short-term nutritional need (i.e. hunger). However, offspring that have experienced contrasting levels of long-term food intake may beg differently for a given level of short-term need, perhaps as a result of developmental differences in behaviour and/or physiology. We tested for the effects of both short- and long-term need on begging and digestion by manipulating food intake rates of the junior and senior nestlings from broods of pied flycatchers, Ficedula hypoleuca. Artificial food intake at natural levels created stable and normal levels of begging in both senior and junior nestlings, over 10h of hand-feeding individuals in isolation. In both classes of nestling, higher than natural levels of food intake led to similar progressive linear declines in begging effort, while lower than natural levels of food intake led to similar progressive increases in begging. However, there were no corresponding changes in digestive efficiency (assimilable mass coefficient). Consistent with previous studies, junior nestlings begged at consistently higher rates throughout compared with senior nestlings. There was also evidence that digestion by junior nestlings was slightly more efficient, but individual variation in begging effort (and change in begging effort) did not correspond to differences in digestive efficiency. These results show that begging does not reflect digestive efficiency across a range of natural food intake rates, and suggest that the honesty of offspring solicitation signals, such as the differences in begging between junior and senior nestlings, are not maintained by contrasting digestive development or function. [ABSTRACT FROM AUTHOR]

Provisioning visits by helpers are normally assumed to confer positive fitness effects on nestlings, but few studies have actually examined the nutritional value of items helpers fed to offspring. In the cooperatively breeding bell miner, Manorina melanophrys, helpers deliver large proportions of ‘lerp’, a sugary secretion of psyllids (Hemiptera; Psyllidae). Although lerp is a major food type of adults, its nutritional value is uncertain, especially since nestlings in other nectarivorous species are usually fed only protein-rich arthropods. Helpers in this system are predominantly male and are often unrelated to broods they aid, suggesting helping might be a sexual display, with any nutritional benefits to nestlings being of secondary importance. Detailed observations revealed that the proportion of lerp delivered increased with nestling age, but that it did not differ between helpers and parents, or between related and unrelated helpers. Variation in delivered biomass (lerp+arthropods) had a positive effect on nestling condition, but variation in the proportion of prey constituted by lerp had no measurable effect on nestling mass or condition. Finally, the total amount of food, nestling body mass and condition were all positively related to the number of helpers provisioning broods. These results are consistent with helping in bell miners operating as cooperative investment in brood fitness. Given that lerp was as effective as invertebrate prey in promoting growth, these results also suggest a valid nutritional role for this easily procured food, presumably facilitated by the unusually early development of nestling digestive tracts to utilize these simple sugars. [Copyright &y& Elsevier]

Research on cooperative breeding has begun to focus on direct fitness benefits gained by helpers, particularly when individuals are unrelated to those they assist. There has been considerable interest in helping possibly operating as a signal, either to show off individual quality to potential mates (‘social prestige’) or to ensure group membership (‘pay to stay’). However, empirical investigation of these phenomena remains sparse. Here we investigate the potential for signalling via provisioning behaviour in the bell miner, Manorina melanophrys, an obligate cooperative breeding species in which the predominantly male helpers are commonly unrelated to breeders. Aggression between birds was extremely rare, and there was little to indicate a pay to stay system. The presence versus absence of members of the breeding pair as a potential audience at the nest had little influence on helper behaviour (e.g. load size/composition, visit duration or frequency). Helpers did produce more individually distinctive vocalizations when in the presence of another helper or the breeding male, although presence of the breeding female (a likely target of male signals) surprisingly had no effect. There was also evidence that nest arrival times coincided somewhat. These results are probably best explained by the helpers and breeding males being involved in additional cooperative behaviours when away from the nest, such as mobbing. Overall, there does not appear to be any evidence that bell miner helpers use nestling provisioning to signal their quality and/or work rate to one another or to either member of the breeding pair. [Copyright &y& Elsevier]

Cooperatively breeding bell miners (Manorina melanophrys) have numerous male helpers assisting at multiple nests. Helpers are often related to the brood they aid, consistent with kin selection. However, there are also unrelated helpers for which other direct fitness benefits are likely to accrue. Bell miner nestlings can become infested by the larvae of a parasitic fly (Passeromyia indecora), which reduce growth and can be fatal. We investigated the amount of time that breeding pairs and helpers closely inspected nests and preened nestlings, behaviors apparently directed at detecting and removing parasites, a form of helping previously unstudied in a cooperative bird. Female breeders provided the greatest antiparasite effort, with breeding males and helpers not differing in effort regardless of their relatedness to the breeding female or brood. We also experimentally infested nests with nonparasitic flies and larvae. All individuals removed the introduced “parasites” if and when they encountered them. Compared with control sessions, inspection effort increased for all birds immediately after the experimental infestations, but only for a short, 5-min period. Further, we detected no changes in helper antiparasite behaviors after the temporary experimental removal of either breeding females or males. Such consistent helping behavior, independent of relatedness and potential audience effects, suggests that antiparasite behavior in bell miners is not particularly kin directed or operating as a signal of helper quality. Our results instead suggest that helper antiparasite effort appears to represent adaptive investment in the welfare of the brood, consistent with direct fitness benefits from group augmentation. [ABSTRACT FROM PUBLISHER]