Molecular insights on the re-colonization of the Limpopo Valley, South Africa, by Southern Ground-Hornbills

Abstract

Southern Ground-Hornbills (Bucorvus leadbeateri) are co-operative breeders that occur in groups of 2–9 individuals. Long life spans, large territory sizes (100 km2), and low reproductive rates render these birds vulnerable to threats such as loss of habitat, persecution, poisoning and loss of suitable nesting sites. In the Limpopo Valley of South Africa, the species is currently re-establishing after a serious decline in numbers. In this study, we use observation, capture and population genetics approaches to gain insights into the nature of the re-colonisation of the Limpopo Valley. We determined the effective population size, genetic diversity estimates, relatedness, parentage, sex ratios, age structure and productivity. The re-colonisation of the Limpopo Valley was shown to have occurred by a number of unrelated individuals. This was demonstrable by the very low levels of average relatedness of the population, as well as the favourable levels of heterozygosity across age and sex categories. Within-group relatedness was as expected, with juveniles related to at least one parent from their natal group. Inferences on breeding behaviour based on genetic testing results provides the first evidence that SGH are not as monogamous as previously thought, with two instances recorded of extra pair copulations. Finally, we demonstrate the application of microsatellite markers to enumerate processes that are difficult to quantify through observation.