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Abstract(s)
Young animals in a broad range of taxa solicit care from their parents
with begging displays, which are used at least partly for competition
among brood or litter mates. The effect of other begging offspring on an
individual’s own begging display varies across studies, however, increasing
its intensity in some, but not changing, or even decreasing it, in others.
One possible reason for this discrepancy is that the potential pay-off
for more intense begging depends not only on how intensely an individual’s
brood or littermates are begging, but also on how long that individual
has been without food. Surprisingly, however, no studies have
focused on how begging responses vary when both factors are varied
simultaneously. We therefore examined how nestling tree swallows,
Tachycineta bicolor, respond to nestmates in relation to both their own
hunger levels and the begging intensity of nestmates. During a period of
food deprivation, we played focal nestlings parental contact calls either
alone (control) or with the begging calls of a nestling deprived of food
for 30–50 (low intensity) or 100–110 min (high intensity). Nestlings
called for longer in response to the low-intensity playback, but, surprisingly,
not in the high-intensity playback, in which they instead delayed
the onset of their calling. All these responses to nestmates were independent
of how long the responding nestling had been deprived of food.
Thus, even in the seemingly intensely competitive environment of a
passerine brood, offspring do not necessarily respond to nestmates with
escalation. This may be because de-escalation is the best competitive
option in some circumstances, or because begging has other functions
besides advertisement of individual need and competition over food
allocation. Certainly, the results illustrate the need for studies of how
nestmate interactions vary across a broad range of contexts.
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Citation
Ethology, 117, 163-170