DIFFERENCES IN BEGGING BEHAVIOR BETWEEN BARN SWALLOW, HIRUNDO-RUSTICA, NESTLINGS

Recent models of parent-offspring communication suggest that nestling begging reliably reflects food requirements, and therefore should incr ease with nestling need. Need may be affected by short-term variations in hunger, as well as by long-term factors such as relative size, gro wth rate and body condition. In the present study, the brood sizes of barn swallows were manipulated to create differences in nestling growt h rate and body condition. The extent to which begging behaviour refle cts these differences was tested. I measured begging behaviour by remo ving nestlings from the nest for three laboratory tests in which tempo ral variations in hunger were controlled, and four target nestlings (s mall and large, from small and large broods) were tested simultaneousl y. Small nestlings and nestlings from large broods had lower growth ra tes and poorer body condition than large nestlings and nestlings from small broods, respectively. Begging was positively correlated with bot h short- and long-term determinants of need. However, when nestlings g rew older (second test), the trend was mixed, mainly because begging l evels dropped in the neediest nestling category (small nestlings from large broods). After nestlings had been exchanged between broods for 2 4 h, small nestlings from large broods improved their growth rate and body condition, but still begged less than expected from their long-te rm need. The results suggest that nestling begging strategies vary wit h brood size and with nestling rank. However, these variations may ref lect not only long-term need, but also nestling response to past exper ience or to variations in the cost and effectiveness of their begging efforts. (C) 1998 The Association for the Study of Animal Behaviour.