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Food or Geology and Badgers in Portugal

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Journal

Oikos, Volume 110,Number 3, September 2005, pp. 441-452(12)

Authors

Rosalino, L. M.;Macdonald, D. W.;Santos-Reis, M.

Abstract

Resource dispersion and badger population density in Mediterranean woodlands: is food, water or geology the limiting factor?

Badgers in Mediterranean cork-oak woodlands live in small groups within territories that embrace a mosaic of habitats where several setts are scattered. Assuming that their population density was related to home range sizes and that this in turn was influenced by food and water availability and the existence of substrate suitable for sett construction, we explored the relationship between these parameters.

Two biotopes were predominantly important in providing food security to badgers in the ‘Grândola’ mountain study area: olive groves and orchards or vegetable gardens. Analysis of the mean total area of these two habitats in the ranges of radio-tracked badgers permitted us to extrapolate to an estimate that the 66 sqkm encompassed eleven areas with the capacity to support badger groups each composed by 6–8 individuals. Since only three groups populated the area we concluded that food availability was not limiting badger density.

Sites with surface water in summer (the dry season) seem sufficient to support more badger groups than existed, leading us to believe that this factor was also not limiting badger density.

Simultaneously, using a logistic regression model and the biophysical characteristics of sett sites as explanatory variables, four predictor variables determined sett location: the existence of a geological fault/discontinuity, ridges, valleys and the distance to abandoned farm houses, of which the former had the higher odds ratio, being thus the best sett location predictor.

56% of the areas predicted with >80% confidence to contain a badger sett were encompassed within a known home range. Therefore, our results suggest that, in Mediterranean cork oak woodlands in SW Portugal, the main factor limiting badger's density is the availability of suitable sites for setts.

However, in areas where suitable sites for burrows existed, but food patches were absent, badgers were not found.

This could indicate that the presence of both factors was necessary for badgers, although in this area sites suitable for digging setts appeared to be the primary limiting factor.

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