Space Invaders

Accipiter tussle on the Cape Peninsula

- Rob Little

Although the displacement of native biota by introduced invasive species is well known and considered to be one of the major threats to biodiversity, it usually involves species introduced directly by human intervention, either intentional or unintentional. Less well documented is the expansion of indigenous species’ ranges as a result of habitat modification by humans. In both cases, potential negative effects of invasive species may be their suppression of native populations through predation, competition, parasitism or disease. One intriguing example is the range expansion by African Goshawks and, more recently, Black Sparrowhawks into the Cape Peninsula and the resultant sympatry with Rufous-breasted Sparrowhawks.

While all three species occur together locally in parts of north-eastern South Africa and all have benefited from the planting of alien trees, only Rufous-breasted Sparrowhawks were historically found in the greater Cape Town area. African Goshawks became regular in the region in the late 1960s and Black Sparrowhawks arrived in the 1990s. Investigation of the changes in the reporting rates for all three species between 1982 and 2018 on the Cape Peninsula, using data from the