Hatching Asynchrony and Kestrels


Kestrels, and many other birds of prey, feed on small mammals which show large fluctuations in numbers from year to year. Hatching asynchrony is the time it takes for the eggs within a clutch to hatch, and hypotheses suggest that asynchrony is an adaptation to unpredictable food levels. I performed food supplementation experiments in the pre-laying and nestling periods to see how individuals adjusted their reproductive effort to a variable food supply. For American Kestrels, laying date and clutch size did not vary, but eggs size increased and hatching asynchrony decreased in response to greater food. These experiments were the first to demonstrate that a bird could manipulate hatching spans facultatively. Hatching asynchrony in Eurasian Kestrels also varied with food abundance, but in the opposite way to American Kestrels.

Wiebe, K.L., E. Korpimaki and J. Wiehn.1998. Hatching asynchrony in the Eurasian kestrel in relation to the abundance and predictability of cyclic prey. Journal of Animal Ecology 67:908-917.

Wiebe, K.L., J. Wiehn and E. Korpimaki. 1998 The onset of incubation in birds: can females control hatching patterns? Animal Behaviour 55:1043-1052.

Wiebe, K.L. 1996. The insurance-egg hypothesis and extra reproductive value of last-laid eggs in clutches of the American Kestrel. Auk 113: 258-261.

Wiebe, K.L. and G.R. Bortolotti. 1996. Proximate effects of food supply on intra-clutch egg size variation in kestrels. Canadian Journal of Zoology 74: 118-124.

Wiebe, K.L. 1995. Explaining intraspecific variation in hatching asynchrony: should birds choose optimal hatching patterns? Oikos 74:453-462.

Wiebe K.L. and G.R. Bortolotti. 1995. Food-dependent benefits of asynchronous hatching in American kestrels. Behavioural Ecology and Sociobiology 36: 49-57.

Wiebe, K.L. and G.R. Bortolotti. 1994. Energetic efficiency of reproduction: the benefits of asynchronous hatching for American kestrels. Journal of Animal Ecology 63: 551-560.

Wiebe, K.L. and G.R. Bortolotti. 1994. Food suppy and hatching spans of birds: energy constraints or facultative manipulation? Ecology 75: 813-823.

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