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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]

‘False feeding,’ where helpers arrive at nests with food but fail to provision the young, has been reported in several cooperative species. This and other potentially ‘deceptive’ behavior has been interpreted as indicating that helping may operate as a signal within such social groups. We critically examine these phenomena in the provisioning behavior of the bell miner Manorina melanophrys. Excessively close observation distances can artificially elevate the rate of false feeding in this (and other) species, but once this had been accounted for, there was little evidence for any ‘deceptive’ behavior by helpers or breeders. Natural and experimentally induced variation in the presence of a potential conspecific audience at the nest did not have any consistent influence upon the rate of false feeds, which was low at 7.94% of 6,880 nest visits. Instead, encountering unexpectedly low levels of brood demand provided a more parsimonious explanation for those visits where helpers failed to feed nestlings or ate the food themselves. Failure to completely transfer a load to nestlings was more likely when the load contained a high proportion of sticky lerp, indicating a simple prey-transfer problem. Finally, individuals that arrived at nests without prey were often members of neighboring breeding pairs, suggesting that these few non-feeding visits may instead involve an information-gathering function. We, therefore, suggest that future studies explicitly exclude the possibility of observer disturbance and all aspects of normal provisioning behavior before applying the terms ‘false feeding’ or ‘deceptive’ and inferring anything more than straightforward helping at the nest. [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]