Electric crows: powerlines, climate change and the emergence of a native invader
Aim Climate change and other anthropogenic global change drivers act in complex, mutually exacerbating ways to alter the abundance and distribution of species. In South Africa, pied crows Corvus albus have increased in numbers and range in recent decades. Popular opinion links these changes to urbanisation and infrastructure development, but there has been no empirical test of this idea. We aimed to clarify the drivers of pied crow population changes in South Africa. Location South Africa. Methods We used publicly available long term datasets, the Southern African Bird Atlas Project and University of Delaware Gridded Climate Database, and spatial data from government bodies, to assess relationships between pied crow population and range changes, land use, infrastructure, urbanisation and climate change. Results Pied crow numbers have increased significantly in the past three decades, but rate of increase varied geographically, with crows declining in the northeast and increasing in the south west of South Africa. Pied crow population changes were strongly correlated with climate change. Crows have benefited most from climate warming in the shrubland biomes of south western South Africa. Pied crows are tree nesters, and within these shrublands, there is a strong positive relationship between the rate of population increase and the density of powerline infrastructure, which may facilitate pied crows' increase by providing nesting sites. Main conclusions Pied crow numbers have increased in response to climate warming, with their spread facilitated by electrical infrastructure in south western South Africa, providing a clear example of compound influence of multiple global change drivers promoting a significant change in species range and reporting rate. Pied crows are generalist predators and there is popular concern about their ecological impact in areas where increases have occurred. We highlight the importance of understanding the ecosystem level implications of increased numbers of pied crows in South Africa's shrubland biomes.