Interannual Synchrony in the Post-Breeding Migration Departure of Yellow-Billed Kites (Milvus aegyptius) From a Roost Site in South Africa

Abstract

Yellow-billed kites (Milvus aegyptius) were counted yearly from 2016 to 2024 at a roost site near Pietermaritzburg, South Africa, in the austral autumn. Kite numbers peaked during a short window between the last days of February and the first few days of March, with a maximum count of 3369 in 2017. There was high interannual synchrony in the departure of kites from the roost, with kites departing just prior to 20–26 March in all nine study years. The consistency of departure timing suggests endogenous cues for migration, not environmental cues, given that abundant food was available at a nearby crocodile farm.