Trends in territory occupancy, distribution and density of the Bearded VultureGypaetus barbatus meridionalisin southern Africa

Abstract

Territory occupancy, distribution and density of the isolated Bearded Vulture Gypaetus barbatus meridionalis population in the Maloti-Drakensberg mountains of southern Africa were assessed between two time periods -former (1960-1999) and current (2000-2012) -to identify population trends. Overall, 190 territories were recorded of which 109 are currently occupied. The number of occupied breeding territories decreased by a minimum of 32% and a maximum of 51% over the past five decades. Territories located on the periphery of the breeding range were more likely to be abandoned than those in the core. The current population is estimated at a minimum of 352 and a maximum of 390 individuals. The breeding range decreased by 27%, restricting the birds to an estimated area of occupancy of 28,125 km 2 . Breeding densities also decreased by 20%, declining from 4.9 to 3.9 pairs/1,000 km 2 . In both periods, higher densities were recorded in the core of the range. Nests were located about 9.0 km apart, a slight increase from the 7.7 km recorded formerly. Inter-nest distances increased with distance from the core range. Further studies are required to ascertain whether productivity or survival is limiting population growth, and whether anthropogenic influences are resulting in the abandonment of territories in the periphery of the range and the subsequent decline in numbers.

Anthropogenic activities influence the abandonment of Bearded Vulture (Gypaetus barbatus) territories in southern Africa

“…Krüger et al (2014) showed that territories in the periphery of the range were more likely to be abandoned than those in the core. We intentionally did not include territory location as a covariate in our models because this variable was correlated with many of our important covariates, and we were interested in the mechanism involved and not merely the spatial pattern of abandonment.…”

“…The Bearded Vulture territories located by Krüger et al (2014) in southern Africa during 2000-2012 (n ¼ 190) formed the baseline of this study. During their 13-year survey period, Krüger et al (2014) determined the current occupancy status of all known breeding territories occupied since the 1960s, the earliest records of nest site locations within the breeding distribution range in the Maloti-Drakensberg mountains (Brown 1992), as well as any additional territories discovered during the survey period.…”

“…During their 13-year survey period, Krüger et al (2014) determined the current occupancy status of all known breeding territories occupied since the 1960s, the earliest records of nest site locations within the breeding distribution range in the Maloti-Drakensberg mountains (Brown 1992), as well as any additional territories discovered during the survey period. Krüger et al (2014) The location of the nest site within each territory was plotted using ArcGIS v.10.0 (ESRI, Redlands, USA). Where a pair had alternative nest sites on the territorial cliff, the location of the most frequently used site was plotted (Krüger et al 2014).…”

“…Krüger et al (2014) The location of the nest site within each territory was plotted using ArcGIS v.10.0 (ESRI, Redlands, USA). Where a pair had alternative nest sites on the territorial cliff, the location of the most frequently used site was plotted (Krüger et al 2014). Around each nest site we created a buffer with a 10 km radius (314 km 2 ; Figure 2).…”

“…The Bearded Vulture (Gypaetus barbatus; Figure 1) is also showing declines throughout much of its range (Mingozzi and Estève 1997, Margalida et al 2008, Birdlife International 2012. Within southern Africa, where the breeding population has declined in both numbers (32-51%) and range (27%) over the past 5 decades (Krüger et al 2014), the species was recently up-listed to Critically Endangered (Krüger in press). The southern African population is restricted to the Maloti-Drakensberg mountains of South Africa and Lesotho, Africa (Brown 1997, Krüger et al 2014, where pairs occupy a territory containing one or more nests on high cliffs generally .1,800 m a.s.l.…”