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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.

Zusammenfassung

Molekulare Einblicke in die Wiederbesiedlung des Limpopo Valley, Südafrika, durch Südliche Hornraben

Südliche Hornraben (Bucorvus leadbeateri) sind kooperative Brutvögel, die in Gruppen von 2–9 Individuen brüten. Lange Lebensspannen, große Brutterritorien (100 km2) und niedrige Reproduktionsraten machen diese Vogelart anfällig für Gefährdungen wie Lebensraumverlust, Verfolgung, Vergiftung und Verlust von geeigneten Nistplätzen. Im Limpopo Valley in Südafrika erholt sich aktuell das Vorkommen dieser Art nach einem deutlichen Bestandsrückgang. In dieser Studie nutzten wir Beobachtungs- und Fangdaten sowie populationsgenetische Ansätze um einen tieferen Einblick in die Struktur der Wiederbesiedlung des Limpopo Valley. Wir bestimmten die aktuelle Populationsgröße, genetische Diversität, Verwandtschaftsverhältnisse, Abstammung, Geschlechterverhältnisse, Altersstruktur und Produktivität. Die Wiederbesiedlung des Limpopo Valley zeigte, dass eine Anzahl nicht-verwandter Individuen auftrat. Dies konnte belegt werden durch ein sehr niedriges Niveau der Verwandtschaftsgrade innerhalb der Population, so wie durch günstige Heterozygositätsgrade über Altersund Geschlechterkategorien. Verwandtschaftsverhältnisse innerhalb einer Gruppe konnten wie erwartet nachgewiesen werden, wobei Juvenile mit mindestens einem Elterntier aus ihrer eigenen Geburtsgruppe verwandt waren. Brutverhaltne und genetische Daten geben erste Belege dafür, dass Südliche Hornraben nicht so monogam sind wie zuvor angenommen: zweimal konnten Kopulationen außerhalb des Paarverbundes nachgewiesen werden. Schließlich zeigen wir die Anwendbarkeit von Mikrosatellitenmarkern zur Verdeutlichung von Prozessen, die durch reine Beobachtungen nur schwer zu quantifizieren sind.

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Acknowledgments

We thank the Percy FitzPatrick Institute (University of Cape Town) for donating samples from the Kruger National Park. Sub-samples of all individuals were sent for biomaterial banking at the National Zoological Gardens of South Africa. Our gratitude to the many farmers in the Limpopo Valley who contributed to this study. We further acknowledge the Mabula Ground Hornbill Project for providing valuable information and the National Research Foundation for financial support towards the molecular genetic analysis. The proposal for this project has been reviewed by the Ethics and Scientific Committee of the National Zoological Gardens of South Africa. Furthermore, all relevant permits and permission from landowners were acquired before capture and sampling of SGH in the Limpopo Province. Finally, we acknowledge the helpful inputs of two anonymous reviewers.

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Correspondence to N. Theron.

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Communicated by M. Wink.

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Theron, N., Dalton, D., Grobler, J.P. et al. Molecular insights on the re-colonization of the Limpopo Valley, South Africa, by Southern Ground-Hornbills. J Ornithol 154, 727–737 (2013). https://doi.org/10.1007/s10336-013-0937-4

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Keywords

  • Southern Ground-Hornbill
  • Microsatellite
  • Genetic diversity
  • Relatedness
  • Co-operative breeding
  • Conservation genetics