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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]