Bird community responses to changes in vegetation caused by increasing large mammal populations in the Serengeti woodlands
Ally K. Nkwabi
A D F , Kris Metzger A B C , Rene Beyers A C , Flora Magige D , Simon A. R. Mduma A C , J. Grant C. Hopcraft A E and Anthony R. E. Sinclair A C
+ Author Affiliations
- Author Affiliations
A Serengeti Biodiversity Program, Tanzania Wildlife Research Institute, PO Box 661, Arusha, Tanzania.
B United States Fish and Wildlife Service, Albuquerque, NM 87102, USA.
C Beaty Biodiversity Centre, University of British Columbia, Vancouver V6T 1Z4, Canada.
D University of Dar es Salaam, Department of Zoology and Wildlife Conservation, PO Box 35064, Dar es Salaam, Tanzania.
E Boyd Orr Centre for Population and Ecosystem Health; Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow, G12 8QQ, UK.
F Corresponding author. Email: ally.nkwabi@tawiri.or.tz
Wildlife Research 46(3) 256-264 https://doi.org/10.1071/WR18001
Submitted: 3 January 2018 Accepted: 9 February 2019 Published: 3 May 2019
Abstract
Context: The increase in density of large tree species, Vachellia robusta and V. tortilis, in the Serengeti Ecosystem of Tanzania has resulted in a decline of small tree species Senegalia senegal, V. hockii, Commiphora spp. This change has occurred since the late 1970s, a consequence of an increase in wildebeest following the extirpation of rinderpest, which reduced the dry grass fuel for fires, resulting in low fire frequencies. Change in tree species raises the question of whether there are indirect consequences for the avifauna that depend on the large trees for food and nesting.
Aims: To determine how an increase in large mammals could influence diversity and distribution of avifauna communities in the Serengeti ecosystem woodlands.
Methods: Data used to estimate changes in density of large and small trees were measured by Point Centre Quarter (PCQ). Bird species were recorded in 19 small-tree sites and 18 large-tree sites in the Serengeti National Park. Richness of bird guilds was calculated in the two habitat complexes (small and large trees), and the ‘rarefaction’ method was used to assess the difference in richness in habitats of the study area. Mean abundance for each species was calculated over the total number of sites for each habitat and compared using the Wilcoxon Rank Sum test to examine how the abundance of avifauna changes with each habitat type.
Key results: There was an increase in the density of large trees in some areas in which they have replaced the original small trees. Such changes have resulted in greater richness of hole nesters and bark feeders, and a greater abundance of large-hole nesters and gleaner bird species.
Conclusions: Because the increase in tree density was caused by an increase in large mammals, we conclude that this increasing mammal population is indirectly increasing richness and abundance of birds using the trees.
Implications: Understanding the influence of large mammal populations on bird distributions has important conservation implications because the Serengeti ecosystem is classified as an important, endemic bird area.
Additional keywords: abundance of birds, distribution, disturbance, large mammals, tree density.
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