Long‐term changes in population size and the age structure and sex ratio of waterbuck in a Sudanian savannah of Burkina Faso

• Published in: African journal of ecology 2021-03, Vol.59 (1), p.132-141
• Main Authors: Konate, Sidiki, Sirima, Djidama, Ardjima, Lankoande, Sanou, Youssouf, Hema, Emmanuel M., Kabre, B. Gustave, Fa, John E., Luiselli, Luca, Petrozzi, Fabio
• Format: Article
• Language: English
• Subjects: abundance; Age composition; age structure; Animals; Aridity; Climate change; Conservation; Conservation status; density; Forests; Global warming; Kobus ellipsiprymnus; Kobus ellipsiprymnus defassa; Poaching; Population; Population decline; Population dynamics; Population number; Population structure; Population studies; Populations; Savannahs; Sex; Sex ratio; Trends; West Africa
• ISSN: 0141-6707; 1365-2028
• DOI: 10.1111/aje.12793

The waterbuck (Kobus ellipsiprymnus), though widespread throughout Africa, is suspected to be declining overall. Data on population numbers and structure are lacking for many parts of its range, especially in West Africa, where the subspecies defassa is found. The aim of the present study was to evaluate the abundance, distribution and attributes of waterbuck populations from the Nazinga Forest Reserve, southern Burkina Faso. We investigated waterbuck population trends in the park using transect data collected in 1985–2019. For the more detailed analyses of population structure and distribution of the animals, we used census data gathered during 2019. Most animals were adults (46.6%), and the sex ratio was heavily skewed towards females (5:1). Most animals were concentrated along the larger rivers. There was no influence of poacher activity on waterbuck distribution. In the long term (1985–2019), the population dynamics of waterbuck can be roughly divided into two main periods: a phase of population increase from 1985 to 2005, and one of ongoing population collapse from 2007 to 2019. Although the declining population trend was obvious, coefficients of determination were low indicating that the years explained poorly the number of individuals and the number of sightings obtained. Waterbuck numbers in the Nazinga Forest Reserve are declining, but we found no single reason to explain this trend. It is likely that a combination of factors, including global warming (increased aridity) and illegal activities such as poaching, is responsible. Because there are probably multiple reasons for the observed waterbuck population decline in our study area, we suggest that a multifaceted approach should be adopted in order to enhance the conservation status of the local waterbuck populations. Résumé Bien que répandu dans toute l'Afrique, le cobe à croissant (Kobus ellipsiprymnus) semble être d’une manière générale en déclin. Les données sur les effectifs et la structure de la population font défaut pour de nombreuses parties de son aire de répartition, en particulier en Afrique de l'Ouest, où se trouve la sous‐espèce defassa. Le but de la présente étude était d'évaluer l'abondance, la répartition et les attributs des populations de cobes à croissant de la réserve forestière de Nazinga, au sud du Burkina Faso. Nous avons étudié les tendances de la population de cobes à croissant dans le parc à l'aide des données des transects recueillies en 1985 et 2019. Pour les analyses