Scientific Services

By conducting two raptor surveys in the Kalahari Gemsbok National Park, we have established a baseline database as an indication of changes to the species composition over time.

The Kalahari Gemsbok National Park (KGNP) is an important refuge for raptors and bustards. Several raptors found in the KGNP are regionally and globally threatened, yet population numbers are infrequently monitored and the last survey took place in 2016.  Therefore, a team from the Endangered Wildlife Trust (EWT) and McGregor Museum in Kimberley made their way to the Kalahari in September 2021. The raptor survey used a road count method where survey vehicles were driven at approximately 20–30 km/h, and all raptors seen perched or flying on both sides of the road were recorded.

Three routes were driven on the first day of the survey. Two teams started from Twee Rivieren, with one team heading north along the Nossob riverbed and the second team heading west along the Auob riverbed before crossing over the upper dune road into the Nossob riverbed. A third team started the count on the 4×4 eco trail route that leads straight to Nossob rest camp through the rugged dunes. On day two, all three vehicles made their way from Nossob to Union’s End to complete the rest of the count. The first vehicle recorded all raptors seen and the other two vehicles made sure that no raptors were missed.

An immature bateleur, this iconic bird of the Kalahari had a successful breeding season (Photo: Beryl Wilson).

Species of special concern seen during the counts included lappet-faced, white-backed and white-headed vultures, as well as kori bustards and martial eagles. The team was excited that the count suggested an increase in diurnal raptor species in 2021 compared to the previous survey in 2016. On the other hand, the data suggested a decrease in nocturnal raptors which may have been due to these cryptic and elusive species being harder to spot in 2021 due to denser foliage. Future monitoring should consider including nocturnal surveys to adequately include all raptor groups.  In the 2021 survey, for example, a single night drive that was not included in the survey data revealed the presence of a number of marsh owls in the vicinity of Nossob. This species was not recorded in either the official 2016 or 2021 surveys.

Raptors deliver valuable ecosystem services and are also considered indicators of ecological health in a system. Their absence, presence, and changes in their distribution or breeding activities provide insights into conservation efforts. Although the exact survey routes in 2016 and 2021 were not identical, the outcome of the 2021 survey suggested that raptor numbers, in general, had increased from the previous survey (511 in 2016 and 1085 in 2021, Fig. 1 for specific species that increased significantly). One possible cause for the lower numbers in 2016 was due to an unreported poisoning event, possibly in Botswana. Several species of eagles and vultures had clearly begun breeding activity earlier in the season (evidenced by viable, lined nests, etc.) but these had been abandoned soon afterward. This suggests that whilst one bird remained on the nest (incubating an egg or a very young chick), the other adult was poisoned at a feeding site. Eventually, the non-return of the poisoned mate would have forced the remaining adult to abandon the egg or chick. The results from the 2021 survey suggest that these raptor species may be recovering from this tragic incident, but may also be attributed to other factors such as better rainfall, local bushfires and various other reasons.

Figure 1. Some of the raptor species that increased between the two surveys in the Kalahari Gemsbok National Park.

A pair of immature black-winged kite siblings each with a prey item provided by the parents. An exceptional number of black-winged kites were seen during the 2021 survey (Photo: Beryl Wilson).

This article was written by Corera Links & Beryl Wilson and originally published in the 2021/2022 Research Report.