Highly skewed sex and age ratios of European Honey Buzzard in southern Africa

Abstract

Sex and age segregation on the non-breeding grounds is common in raptor species. We studied the European Honey Buzzard (Pernis apivorus) on its southern African non-breeding grounds to examine changes in sex and age ratios over a period of recent population expansion (2002–2017). Photographs from multiple open sources were analysed. The adult population was found to be overwhelmingly female (93.3%) with no significant variation over months, years, or latitudes. This supports the arrival-time hypothesis, which states that the sex responsible for establishing the breeding territory (the male in honey buzzard) will spend the non-breeding period closest to the breeding grounds, allowing them to reduce intrasexual competition for breeding territories. Juvenile and second year birds (41.6% of the population) were more common at lower elevations, as well as further south in the sub-region. This is likely due to a funnelling effect of inexperienced juvenile birds further south and to coastal zones. In addition, juvenile birds do not return to the breeding grounds for at least 2 years, so may be more likely to migrate further south. Finally, second year birds increase later in the austral summer. This may be a result of both juvenile birds moulting into more adult plumage, and a southward intra-continental movement of young honey buzzards in Africa.