Breeding distribution and seasonality of Whiskered Terns Chlidonias hybrida in southern Africa

The Whiskered Tern Chlidonias hybrida has a fragmented distribution in southern Africa, but regional breeding occurrence has never been investigated. Using an exhaustive search of historical and modern sources, we collated breeding records and mapped breeding distribution and seasonality to shed light on their complex dynamics in the region. Between 1901 and 2026, we found 140 breeding records from seven countries, of which over half were from South Africa. The mean ± SD nesting colony size was 16.1 ± 14.6 nests across the breeding range. South Africa and Namibia had marked seasonality in breeding, with records exclusively during the summer rainy season. A lack of seasonal patterns in Botswana supports the likelihood of opportunistic breeding there. In Zambia, nesting in the late rainy season indicates different movement patterns from populations at higher latitudes, where some may migrate north into the Zambian breeding area while northern birds are still nesting. These findings further reveal complex regional dynamics that could be addressed with tracking research.