Effect of growth and hatching asynchrony on feldging age of black and red kites

Abstract

We studied the effect of growth rate, final size, hatching sequence, hatching asynchrony, and fledging asynchrony on the fledging age of Black and Red kites (Milvus migrans and M. milvus). Feather growth explained 43% and 38% of the variance in fledging age of Black and Red kites, respectively. Fledging age increased with hatching sequence and increased fledging asynchrony in relation to initial hatching asynchrony of both species, especially in broods of three chicks. Once the effect of growth was removed, no differences in fledging age related to hatching sequence were found in the Red Kite, but there was still a delay in fledging of third-hatched Black Kite chicks. Synchronous fledging of first- and second-hatched Black Kite chicks seemed to occur when both chicks had grown at a similar rate, and was caused by a delay in the fledging of the first-hatched chick. First-hatched Black Kite chicks did not delay fledging if second-hatched chicks experienced reduced growth. Differences between the two species in the third-hatched-chick fledging delay could be due to differences in nest provisioning by adults during the postfledging dependence period. Red Kites reduced provisioning to the nest as soon as the first chick fledged, while Black Kites maintained nest provisioning longer. No evidence was found supporting the idea that parents may reduce feedings to hasten first flight of their offspring