Family break‐up in Black and Red Kites Milvus migrans and M. milvus: is time of independence an offspring decision?

Abstract

I observed the natural process of family break‐up in 13 families of Black Kites Milvus migrans and five families of Red Kites M. milvus in which fledglings had been individually marked. In other broods, I performed experiments which modified the parental investment fledglings received by supplementing nests of both species with food or transferring Black Kite chicks to nests with younger or older chicks of the same species.The time of family break‐up in the Black Kite is mainly an offspring decision which is not affected by an artificial increase of parental investment. The duration of the post‐fledging period was not increased in Black Kites that were given supplementary food. Chicks transferred to nests with a younger chick did not extend the post‐fledging period, nor did chicks transferred to nests with an older chick shorten the post‐fledging period. In Red Kites, parental investment seemed to have more influence on the timing of the family break‐up. Red Kite adults invested less as parents than did Black Kites during the post‐fledging dependence period, and in nests where supplementary food was given, Red Kite fledglings stayed attached for a longer period.