Wolf density is positively correlated with the density of diurnal rodents on a sub-population level in the Bale mountains (Sillero-Zubiri, 1994), indicating that resources are limiting for Ethiopian wolves. There is also evidence that reproductive success is lower in high-density populations, as evinced by faster rates of population increase in the Web Valley during the years following decimation by rabies in the early 1990s (Marino, 2003). I will test whether the reproductive success of a pack, measured by emergence litter size, pup survival rates and number of offspring recruited to the pack at one year of age, are correlated with spatial and temporal variation in prey abundance. I will also investigate the relationship between habitat quality, territory configurations and wolf population structure. Marino (2003) found that territories were configured to contain similar amounts of prey-rich habitat types, so that where key habitats were more dispersed, territories were larger. My research will incorporate a wider range of habitats and population densities, and further build upon the habitat-wolf density relationship elucidated in Sillero-Zubiri (1994).

The rabies epidemic in 2003-4 (Randall et al., 2004) resulted in a catastrophic decline in the Web Valley to one third of pre-rabies numbers. My research takes advantage of this ‘natural experiment’ to contrast wolf territoriality and breeding success in the same area at radically differing densities (1.2 wolves km-1 pre-rabies versus 0.4 wolves km-1 post-rabies).

For the purpose of this study, habitat ‘quality’ is divided into several components:
• Resource availability, specifically the abundance of particular prey species;
• Human-mediated interference, the latter incorporating the impact of livestock, domestic dog and human presence and activities within the wolf range, and
• Physical characteristics of vegetation and topography within each territory, which may affect hunting efficiency independently of their effect on prey density.

Grass rat densities will be calculated from live-trapping grids, and giant molerat densities from live-observation plots and counts of active holes. Densities of non-fossorial prey, livestock, humans and domestic dogs are surveyed using line-transects. Vegetation is surveyed using point sampling on rodent grids, at transect observations and throughout territories in the Web Valley and Sanetti Plateau. At each vegetation sampling point the following data are collected:
• Plant species, to reveal habitat preferences of each prey species;
• Height, as an index of the depth of cover and volume of forage available;
• Plant part & colour, to indicate nutritional quality and seasonal variation in water availability, and
• Substrate (earth/rock/water), which also functions as a surrogate for soil depth.
Additional variables to be derived from these data are percent cover, mean height, diversity (Shannon-Weiner) & evenness (Simpson).

This design of concurrent vegetation and prey sampling is being used to develop a forecasting model, from which prey abundance can be extrapolated for entire territories and habitat classes based on their vegetation. A Bale-wide prey density map will be created by combining all prey and vegetation survey data with a habitat map derived from remotely-sensed data. A 30m resolution habitat map of all the afro-alpine areas occupied by Ethiopian wolves in Bale has been created by classifying a Landsat ETM+ image. An unsupervised classification produced fifty-three distinct habitat types, encompassing the whole range of afro-alpine vegetation, from reed-beds and perennial water bodies to Alchemilla meadows and molerat-dense mima mounds which can be practically devoid of vegetation. The vegetation samples will be used to quantify vegetation parameters such as species composition, height and cover in each habitat, and further ground-truthing data in the form of qualitative descriptions of homogenous habitat patches and over 200 photographs from known locations will be used to test and refine the classification. For those classes for which an adequate number of prey observations exist, the mean density and variability in density for each prey species will be calculated directly from the prey surveys. For classes with smaller sample sizes, prey densities will be calculated using the forecasting model.

Relevant publications

Marino, J., 2003. Spatial ecology of the Ethiopian wolf, Canis simensis. D.Phil. thesis. Wildlife Conservation Research Unit, Department of Zoology, University of Oxford, Oxford.

Randall, D.A., Williams, S.D., Kuzmin, I.V., Rupprecht, C.E., Tallents, L.A., Tefera, Z., Argaw, K., Shiferaw, F., Knobel, D.L., Sillero-Zubiri, C., Laurenson, K.M., 2004. Rabies in endangered Ethiopian wolves. Emerging Infectious Diseases 10, 2214-2217.

Sillero-Zubiri, C., 1994. Behavioural ecology of the Ethiopian wolf, Canis simensis. D.Phil. thesis. Wildlife Conservation Research Unit, Department of Zoology, University of Oxford, Oxford.