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.

Campbell Murn,Jean‐Marc Thiollay,Munir Z. Virani,Peter Mundy,Graham J. Holloway,Wendy D. Borello

doi:10.1002/ece3.1931

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 km(2) 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 100km 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.

Highlights

Vultures are threatened across many parts of the world (Ogada et al 2012) and more than half (69%) have an unfavorable conservation status (BirdLife, 2015)
Size was listed for all National Parks and Category II protected areas (PAs), but 13.8% (n = 663) of the listed PAs did not have a reported size, which meant they were missed by the initial selection criteria
Each of the remaining 11 areas was assessed according to size and shape within the GIS shape files and a conservative estimate was made that these 11 PAs covered between 7000 and 10,000 km2

Summary

Introduction

Vultures are threatened across many parts of the world (Ogada et al 2012) and more than half (69%) have an unfavorable conservation status (BirdLife, 2015). Over large parts of Africa vultures are severely threatened and populations of a 2016 The Authors. Using protected Areas to Estimate Population most species are declining (Rondeau and Thiollay 2004; Thiollay 2007a; Ogada and Buij 2011; Virani et al 2011; Kru€ger et al 2014), and these ongoing declines mean that the conservation status of most species on the continent is considered critical (Ogada et al 2015)

Methods

Results

Conclusion