Investigating the breeding success of cape vultures (Gyps Coprotheres) at Bonwalenong and manong yeng breeding sites in the Tswapong Hills, Botswana

Abstract

The endangered Cape Vulture (Gyps coprotheres) breeds only in hilly areas of southern Africa. Botswana is a home of these cliff-nesting species, with its largest colonies found in the southeast (Mannyelanong Hill) and eastern (Tswapong Hill complexes) parts of the country. Out of five colonies, only two large colonies at Moremi (Bonwalenong site) and Goo-Tau (Manong Yeng site) and one small colony near Lerala (Kukubye site) villages remain. The current breeding status and population of Cape Vultures at the two large colonies (Bonwalenong and Manong Yeng) was last studied in 1999. Therefore this study used both direct observations and Generalized Linear Model to estimate the breeding population and breeding success and investigated nest site and cliff characteristics at the two large colonies remaining in the Tswapong Hills. The study results were compared with data from the 1990s. A total of six visits were made throughout the breeding season, where a total of n=280 (Bonwalenong, n=200 and Manong Yeng, n=80) pairs were identified and monitored. When comparing the breeding population monitored from 1992-1999 and then not again until 2017, the results showed no significant difference in the breeding population compared to the previous studies. However, study results showed that the Bonwalenong colony has recovered from n=10 pairs in 1999 to n=200 in 2017. Over the same period, Manong Yeng had a higher number of breeding pairs n=158 declined to n=80 in 2017. Investigations of breeding success showed that >50% of nestlings that failed to fledge occurred between June and September months which coincided with the incubation and nestling period. Breeding success estimates for 2017 at both sites significantly differed with Manong Yeng estimated at 23.8% for the 80 pairs monitored and Bonwalenong at 43.5% for the 200 pairs monitored. There was also a significant variation of breeding success among the three cliff faces especially between Bonwalenong south facing cliff and Manong Yeng cliff. Distance of the colony to the nearest village, height of nest and aspect of cliff were found to be important for breeding success and nest site selection. Out of the total areas modeled, <20% demonstrated the suitable habitat for the nesting and breeding of Cape Vultures. These potentially habitable areas fell in the hill ranges in the Tswapong south region where the two large colonies occur. Consistent monitoring and research are required to better understand population dynamics and the key factors influencing chick survival. Results from this study are vital for governmental and non-governmental stakeholders involved in wildlife conservation and management.