AVIS-IBIS

Birds of Indian Subcontinent

Warm temperatures lead to early onset of incubation, shorter incubation periods and greater hatching asynchrony in tree swallows Tachycineta bicolor at the extremes of their range

Publication Type:Journal Article
Year of Publication:2006
Authors:Ardia, DR, Cooper, CB, Dhondt, AA
Journal:Journal of Avian Biology
Volume:37
Issue:2
Date Published:2006
ISBN Number:1600-048X
Keywords:Hirundinidae, Hirundo, Hirundo rustica, Iridoprocne bicolor, Tachycineta, Tachycineta bicolor
Abstract:The onset of incubation varies in birds, with many species beginning incubation prior to clutch completion. Here we examine whether early onset is more likely to occur during high temperatures, a critical prediction of the egg-viability hypothesis, which suggest that birds begin incubation prior to clutch completion in order to maintain egg-viability. We examined onset of incubation in tree swallows Tachycineta bicolor at two locations at the extremes of their breeding range, Alaska and Tennessee. A majority of individuals (68%) began incubation prior to clutch completion. While females in Tennessee were more likely to begin incubation early, there was no difference between sites when differences in temperatures inside nestboxes were controlled in analyses. Rather, early onset of incubation was predicted by the proportion of daily temperatures above physiological zero during laying, a critical prediction of the egg viability hypothesis. Both warm weather and early onset led to shorter incubation periods and increased levels of hatching asynchrony. We found no effect of timing of nesting, female body condition index or clutch size on the probability of beginning incubation prior to clutch completion. Our results are consistent with the egg viability hypothesis, not consistent with a threshold clutch size rule, and do not support the hurry-up hypothesis, that individuals breeding later in the season would begin incubation early to reduce the time spent nesting. Overall, our results suggest that broad scale geographic differences in incubation behaviour may be explained by individual-level responses to environmental conditions.
URL:http://dx.doi.org/10.1111/j.0908-8857.2006.03747.x
Short Title:Journal of Avian Biology
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