Using Africa's protected area network to estimate the global population of a threatened and declining species: a case study of the Critically Endangered White‐headed Vulture Trigonoceps occipitalis

Abstract

The White‐headed Vulture Trigonoceps occipitalis (WhV) is uncommon and largely restricted to protected areas across its range in sub‐Saharan Africa. We used the World Database on Protected Areas to identify protected areas (PAs) likely to contain White‐headed Vultures. Vulture occurrence on road transects in Southern, East, and West Africa was adjusted to nests per km2 using data from areas with known numbers of nests and corresponding road transect data. Nest density was used to calculate the number of WhV nests within identified PAs and from there extrapolated to estimate the global population. Across a fragmented range, 400 PAs are estimated to contain 1893 WhV nests. Eastern Africa is estimated to contain 721 nests, Central Africa 548 nests, Southern Africa 468 nests, and West Africa 156 nests. Including immature and nonbreeding birds, and accounting for data deficient PAs, the estimated global population is 5475 ‐ 5493 birds. The identified distribution highlights are alarming: over 78% (n = 313) of identified PAs contain fewer than five nests. A further 17% (n = 68) of PAs contain 5 ‐ 20 nests and 4% (n = 14) of identified PAs are estimated to contain >20 nests. Just 1% (n = 5) of PAs are estimated to contain >40 nests; none is located in West Africa. Whilst ranging behavior of WhVs is currently unknown, 35% of PAs large enough to hold >20 nests are isolated by more than 100 km from other PAs. Spatially discrete and unpredictable mortality events such as poisoning pose major threats to small localized vulture populations and will accelerate ongoing local extinctions. Apart from reducing the threat of poisoning events, conservation actions promoting linkages between protected areas should be pursued. Identifying potential areas for assisted re‐establishment via translocation offers the potential to expand the range of this species and alleviate risk.

Densities and population sizes of raptors in Uganda’s conservation areas

“…We further assumed that small CAs, with sufficient savanna to support only a single pair of a given species, would be occupied only intermittently. Following Murn et al (2016), we took a conservative approach to estimating the number of breeding pairs present, by excluding CAs where the amount of savanna was less than double that required to support one pair of the target species.…”

“…To fully appreciate the implications of farmland conversion for such species it is important to determine the degree to which they are dependent on protected areas, their density within savanna, and hence the number of pairs each PA is capable of supporting. In a detailed case study, Murn et al (2016) applied this approach to the White-headed Vulture Trigonoceps occipitalis, a species now largely confined to PAs throughout its global range. Their findings highlight the fragmentary nature of the species' global distribution, showing that 78% of occupied PAs are each likely to support fewer than five breeding pairs.…”

“…Their findings highlight the fragmentary nature of the species' global distribution, showing that 78% of occupied PAs are each likely to support fewer than five breeding pairs. Furthermore, most of the PAs supporting larger breeding populations (of at least 20 breeding pairs) were separated from other occupied PAs by at least 100 km (Murn et al 2016). The insights provided by this approach are key to understanding the population status of Africa's PA-dependent raptors more fully.…”

Local knowledge and perceptions of vulture conservation in communities living adjacent to the northern Gonarezhou National Park, Zimbabwe.

“…Recent studies have revealed that vulture populations have declined, particularly in Africa (Virani et al 2011, Ogada et al 2012, Murn et al 2016, Ogada et al 2016. Accordingly, most species are now listed on the International Union for the Conservation of Nature and Natural Resources (IUCN) Red List as Endangered or Critically Endangered (IUCN 2016).…”

Using areas of known occupancy to identify sources of variation in detection probability of raptors: taking time lowers replication effort for surveys

“…The species is critically endangered [18] and with a global population of approximately 5500 birds [19], they are difficult to find. To estimate the detection probability of large savannah raptors and the factors that affect it, in this study we used encounter rates of white-headed vultures during surveys in areas of known vulture occupancy.…”