Avian range changes and climate change: a cautionary tale from the Cape Peninsula

Evidence from the Northern Hemisphere and simple theoretical models both predict that climate change could force southern African birds to undergo poleward range shifts. We document the chronology and habitat use of 18 regionally indigenous bird species that colonised the extreme south-western corner of Africa after the late 1940s. This incorporates a period of almost four decades of observed regional warming in the Western Cape, South Africa. Observations of these colonisation events concur with a 'climate change' explanation, assuming extrapolation of Northern Hemisphere results and simplistic application of theory. However, on individual inspection, all bar one may be more parsimoniously explained by direct anthropogenic changes to the landscape than by the indirect effects of climate change. Indeed, no a priori predictions relating to climate change, such as colonisers being small and/or originating in nearby arid shrublands, were upheld. This suggests that observed climate changes have not yet been sufficient to trigger extensive shifts in the ranges of indigenous birds in this region, or that a priori assumptions are incorrect. Either way, this study highlights the danger of nave attribution of range changes to climate change, even if those range changes accord with the predictions of climate-change models. Nonetheless, studies of artificially enriched faunas, such as that of the Cape Peninsula, and the dynamics of these observed range shifts, may provide insight into processes likely to take place should climate change trigger significant poleward movement by Southern Hemisphere birds.