One Park, Many Worlds

Trophic Interactions

Trophic Interactions - The Bale Mountains Ecosystem Project

The Afroalpine ecosystem has a simple and visible trophic structure with Ethiopian wolves and a diverse assemblage of raptors, including the only sub-Saharan population of Golden Eagle Aquila chrysaetos, feeding almost exclusively upon a guild of burrowing rodents, including 10 species endemic to Ethiopia. The rodents, which occur at incredibly high densities, feed exclusively on forbs and grasses. As rodents form the main prey for raptors and wolves, their population regulation is a key issue in the conservation of this ecosystem. However, there are currently no data available on the numerical and functional response of the raptors nor is there any information on the regulatory effects of wolf and raptor predation on rodent population dynamics.

This study is investigating the possible regulatory effects of raptor and wolf predation on the Afroalpine rodent communities of the Bale Mountains National Park. Of main interest with respect to raptors is the guild of Aquila eagles with breeding golden eagle A. chrysaetos, black eagle A. verreauxii, teagle A. rapax and migrant steppe eagle A. nipalensis, lesser-spotted eagle A. pomarina and greater-spotted eagle A. clanga. The three breeding eagles occur at remarkably high density (combined density up to 10 pairs per 100km2) as do Augur buzzards Buteo augur and Lanner falcons Falco biarmicus which are ubiquitous throughout BMNP (combined densities up to 50 pairs per 100 km2). Migrant steppe eagles are very abundant during the dry season. Furthermore, as wolves and raptors both prey predominantly on rodents there is considerable potential for intra-guild competition We are also assessing dietary overlap and use of space by the different species of raptors and the wolves to assess the potential for intra-guild competition. The study will be of immediate value in planning conservation action for the raptor community, the Ethiopian wolf and the Afroalpine ecosystem upon which they depend.

Field work has focussed on the following areas: locating breeding raptors, collection of pellets and prey remains from raptor nests, density estimation of resident and migrant raptor populations by scan sampling, density estimation of avian and mammalian prey populations by distance sampling on transects, density estimation of small mammal populations by capture-mark-recapture trapping programmes, quantification of small mammal – habitat relationships by removal trapping.

This research was initiated by Simon Thirgood of the Macauley Institute with field work conducted by Anteneh Shemelis and Ermias Admasu in collaboration with Prof. Afework Bekele of Addis Ababa University and logistical support from the Ethiopian Wolf Conservation Programme. Financial support has been provided by the Wildlife Conservation Society, Conservation International, the Peregrine Fund, the British Ecological Society and Frankfurt Zoological Society.

Bale Mountains National Park