Abstract
Cape vulture Gyps coprotheres populations have declined across their range due to multiple anthropogenic threats. Their susceptibility to fatal collisions with the expanding power line network and the prevalence of carcasses contaminated with illegal poisons and other threats outside protected areas are thought to be the primary drivers of declines in southern Africa. We used GPS-GSM units to track the movements and delineate the home ranges of five adult (mean ±SD minimum convex polygon area = 121,655±90,845 km2) and four immature (mean ±SD minimum convex polygon area = 492,300±259,427 km2) Cape vultures to investigate the influence of power lines and their use of protected areas. The vultures travelled more than 1,000 km from the capture site and collectively entered five different countries in southern Africa. Their movement patterns and core foraging ranges were closely associated with the spatial distribution of transmission power lines and we present evidence that the construction of power lines has allowed the species to extend its range to areas previously devoid of suitable perches. The distribution of locations of known Cape vulture mortalities caused by interactions with power lines corresponded to the core ranges of the tracked vultures. Although some of the vultures regularly roosted at breeding colonies located inside protected areas the majority of foraging activity took place on unprotected farmland. Their ability to travel vast distances very quickly and the high proportion of time they spend in the vicinity of power lines and outside protected areas make Cape vultures especially vulnerable to negative interactions with the expanding power line network and the full range of threats across the region. Co-ordinated cross-border conservation strategies beyond the protected area network will therefore be necessary to ensure the future survival of threatened vultures in Africa.
Highlights
Vultures in the Gyps genus are obligate scavengers of vertebrate carcasses and provide vital ecosystem services by recycling carrion, thereby limiting the development and spread of disease and maintaining energy transfer through food webs [1,2]
Under the current rate of expansion of the power line network it is important to investigate the relationship between power lines and vultures in southern Africa, in a spatial context to allow mitigation measures to be implemented in key areas [10,16]
The five adult vultures traversed larger home ranges than five adult Cape vultures tracked in Namibia, such comparisons should be considered with caution because breeding attempts by the vultures from this study could not be confirmed during colony surveys
Summary
Vultures in the Gyps genus are obligate scavengers of vertebrate carcasses and provide vital ecosystem services by recycling carrion, thereby limiting the development and spread of disease and maintaining energy transfer through food webs [1,2]. Their longevity, delayed maturity and low reproductive rates mean that even minimal reductions in adult survival rates or the proportion of immatures reaching breeding age could result in population declines [3,4]. Under the current rate of expansion of the power line network it is important to investigate the relationship between power lines and vultures in southern Africa, in a spatial context to allow mitigation measures to be implemented in key areas [10,16]
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