Plural-breeding Australian Magpies Gymnorhina tibicen dorsalis Nesting Annually in the Same Tree

Abstract

A single social group of plural-breeding Western Australian Magpies Gymnorhina tibicen dorsalis had two concurrently active nests in the same Marri Corymbia calophylla tree over three consecutive years 2003–05. Western Australian Magpies are social birds that breed co-operatively, although they have not been reported previously with nests in the same tree. These nests were positioned such that the centre of the tree did not obstruct the visibility from one to the other. Nesting this closely may facilitate intraspecific brood parasitism, which has been reported in plural-breeding Magpies. Double nesting in this tree was most likely caused by the tree’s isolation in a field that formed most of the group’s feeding range, within which Magpies generally showed aggression only to larger birds.