Palearctic White Storks Ciconia ciconia in the Western Cape, South Africa, in the 20th century

Abstract

At the start of the 20th century, the southern limit of the nonbreeding range of the White Stork Ciconia ciconia, a migrant from the Palearctic, was considered to be at the Orange River; they moved around opportunistically in this area to feed on swarms of locusts. Until around 1935, White Storks were vagrants in the Swartland and Overberg agricultural regions of the Western Cape; after that they were present in small numbers, occurring mainly when there were drought years over the traditional range. From the late 1950s, numbers in the Overberg gradually increased. However, between 1985 and the end of the 20th century, White Stork abundance fluctuated widely here, but the overall trend was no longer upwards. Notably the increase in abundance in the Western Cape occurred while the population in Europe was decreasing, and the southward extension of the nonbreeding range was therefore unexpected. The explanation might lie in impact of locust control in the traditional nonbreeding areas. Locust control became consistent and persistent from around the mid-1940s, with the introduction of benzene hexachloride as control agent. White Storks were not impacted by feeding on poisoned locusts; however, it is likely that locust control gradually reduced the size and abundance of their swarms. In the face of reduced food availability, White Storks started occurring in increased numbers in the croplands of the Overberg. In their pristine state this area would have been unsuitable habitat for White Storks. The transformation to croplands had taken place several decades before they were extensively used by White Storks.