Differences in begging behaviour between barn swallow,Hirundo rustica, nestlings

Abstract

Recent models of parent–offspring communication suggest that nestling begging reliably reflects food requirements, and therefore should increase with nestling need. Need may be affected by short-term variations in hunger, as well as by long-term factors such as relative size, growth rate and body condition. In the present study, the brood sizes of barn swallows were manipulated to create differences in nestling growth rate and body condition. The extent to which begging behaviour reflects these differences was tested. I measured begging behaviour by removing nestlings from the nest for three laboratory tests in which temporal variations in hunger were controlled, and four target nestlings (small and large, from small and large broods) were tested simultaneously. Small nestlings and nestlings from large broods had lower growth rates and poorer body condition than large nestlings and nestlings from small broods, respectively. Begging was positively correlated with both short- and long-term determinants of need. However, when nestlings grew older (second test), the trend was mixed, mainly because begging levels dropped in the neediest nestling category (small nestlings from large broods). After nestlings had been exchanged between broods for 24h, small nestlings from large broods improved their growth rate and body condition, but still begged less than expected from their long-term need. The results suggest that nestling begging strategies vary with brood size and with nestling rank. However, these variations may reflect not only long-term need, but also nestling response to past experience or to variations in the cost and effectiveness of their begging efforts.