When do canary parents respond to nestling signals of need?

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Abstract
Parent birds at the nest face a brood of nestlings that are jostling, gaping, calling and posturing. Recent empirical work on food distribution among the brood has demonstrated a strong effect of close proximity to the parent in determining the amount of food allocated to each chick. Chick position in the size hierarchy and level of chick food deprivation have previously been shown separately to influence chick proximity to the feeding parent, but it is not clear how these two factors interact. Experiments on canaries, described here, aimed first to investigate the interaction of size and hunger on chick proximity to the feeding parent and, second, to discover whether parents responded to any other chick behaviours when distributing food within the brood. Manipulations of levels of food deprivation with respect to chick size indicated that although size had the strongest effect on chick proximity to the parent, hunger level could also play a part. When chick position in the nest was controlled experimentally, parents responded to other cues when allocating food. It is suggested that the broad food distribution patterns of the parents are influenced by size-dependent chick behaviours, such as proximity to the parent. Within these broad patterns parents respond to short-term fluctuations in chick hunger as signalled by the posturing and calling behaviours of the chick.