KARASOV, W.H.; MCSWAN, E.L.; WRIGHT, J.: Begging and digestion by nestling Pied flycatchers in relation to short- and long-term nutritional need

An important question regarding parent-nestling interactions is how features of begging relate to nestling physiological status. Nestling birds of different ages, sizes, or developmental histories may have different nutritional needs. How accurately does nestling begging reflect subtle differences in nestling state? We describe methods for studying this using single-day trials with Pied flycatchers (Ficedula hypoleuca). Nestlings 7 days old were removed from nests for 10-hour trials during which feeding and excretion rate and begging behavior were monitored. Nestling size differed due to hatching asynchrony, and feeding level with a formulated diet was set at 60, 100, and 150% of the expected normal energy intake level. All measures of begging (e.g., the number of calls, the rate of calling, the length of begging, the latency time before beginning to beg, the height of begging) were subsumed within one principal component. As feeding level increased, apparent digestive efficiency was constant and begging intensity declined. There was evidence that smaller nestlings begged more intensively and digested food more efficiently. Thus, begging signals, and possibly digestive physiology, may reflect not just recent feeding history, or short-term need, but also longer-term requirements in terms of the extent of nestling growth attained. Results are interpreted in relation to the idea of honest begging and possible competitive begging strategies. Supported by the Leverhulme Trust and NSF.