The breeding status and colony dynamics of Cape Vulture Gyps coprotheres in Botswana

Abstract

Cape Vulture Gyps coprotheres is endemic to southern Africa and is globally threatened. Colonies in Botswana comprise part of one of the two core breeding areas in the species's range, and very little has previously been published about them. Ground censusing of 11 Cape Vulture sites in Botswana was undertaken from 1992 to 1999, continuing a monitoring programme initiated by the authors in 1984. Survey methods and census procedures are documented. The potential Cape Vulture breeding population in Botswana is estimated to be about 600 pairs, comprising at least 100 pairs at Mannyelanong in the south-east and about 500 pairs in eastern Botswana. This represents an increase from previous estimates, and reflects improved census techniques rather than an increase in population size. The mean turnover rate of nest site usage from one year to the next averaged 21% at Mannyelanong, and was about 26% at Manong Yeng in eastern Botswana. Annual productivity of nest sites increased with the number of years the site had been occupied. Over the eight years of study eggs were laid in at least 436 of 477 nests (91.4%) at Mannyelanong; chicks survived to mid season (60–80 days old) in 327 nests (75% of eggs laid), and fledged (best estimate) in 248 nests (56.9% of eggs laid and 52% of pairs attempting to breed). In eastern Botswana eggs were laid in at least 1,825 of 2,101 nests (86.9%); chicks survived to mid season in 1,272 nests (69.7% of eggs laid). Two seasons have been excluded for eastern Botswana (1994 and 1995) due to incomplete data, and breeding success can be estimated only from 1997 to 1999: of 990 eggs laid out of 1,108 nests, chicks fledged in 384 nests (38.8% of eggs laid and 34.6% of pairs attempting to breed). The eastern Botswana breeding population remains in a state of flux following the collapse of a primary colony that was the country's Cape Vulture stronghold. Conservation concerns and the vulnerability of Cape Vulture sites are discussed.