Spatial organization and behaviour of badgers (Meles meles) in a moderate-density population

Abstract

Badgers are carnivores that show considerable variation in their social and spatial organization. At the westernmost part of their range, in Britain and Ireland, variation in spatial organization appears to be determined by the availability of resources. However, the majority of studies has focussed at one end of the social/spatial spectrum, where population densities are high and adjacent territories are contiguous and non-overlapping. To examine whether the same limiting factors appear to apply across a wider range of badger densities, we established a study site in a predominantly coniferous habitat within an upland area of northeast England, where population densities were predicted to be low. Seasonal home ranges of individual badgers were largest in autumn, followed by summer and spring, then winter. This pattern is reflective of the likely seasonal changes in food availability within the area, as opposed to being related to breeding patterns. There were also significant correlations between territory size and the number of grassland patches (positive) and the proportion of grassland (negative), which are consistent with predictions from the Resource Dispersion Hypothesis. Although badgers at the site were living at low to moderate densities relative to many other studied populations in Britain, they showed patterns of spatial organization that were close to those of high-density populations. The nature of the relationship between resource availability and abundance patterns is likely to have important consequences for the conservation and management of badgers and other species that show flexible spatial organization.

Appendix

Determination of diet based on techniques similar to that described by Reynolds and Aebischer (1991) and C. Emes (personal communication)

Faecal samples were defrosted thoroughly overnight before analysis and then oven-dried at 55°C for at least 24 h until a constant dry weight was reached. The dried scat was weighed to the nearest ±0.1 g and then rehydrated in warm water, to aid breaking it down. The slurry was then transferred into a 500-μm Endecott and washed under running water to liberate as much soil as possible, collecting the run-off in a large beaker. The contents of the beaker were strained through a 150-μm Endecott to retain the microfraction containing earthworm chaetae and to remove any excess silt. The contents of the sieve were then transferred into a glass beaker of known weight. The microfraction was labelled and dried at 55°C until a constant dry weight was reached. The sample was weighed to the nearest ±0.01 g and the weight of the glass beaker subtracted to give the total microfraction. To estimate the number of earthworms consumed, the microfraction was gently homogenised with a spatula and a small subsample was removed, weighed and transferred into a 1-cm² gridded transparent dish. A small amount of 70% alcohol was added to allow even distribution of the subsample across the dish. The number of chaetae was counted across a subsample of 1-cm squares of the dish using a 35× binocular microscope. The total number of chaetae in the initial sample was then extrapolated from the number of chaetae in the subsample. The number of worms per unit weight of faeces was calculated on the assumption that one Lumbricus terrestris yields approximately 1,080 chaetae (derived from Wroot 1985). Although other Lumbricus species may be consumed (e.g. Lumbricus rubellus; Kruuk and Parish 1981), the closely related species are considered to be similar in body size and have a similar number of segments per worm (Wroot 1985), reducing the possible error associated with estimating the number of chaetae per earthworm consumed.

The remaining macrofraction in the 500-μm Endecott was collected and placed into a large shallow white dish. It was initially inspected by eye for any food remains and then submerged in water to release any trapped items. Each component of the macrofraction was separated and dried at 55°C to a constant weight. Fruit stones and seeds were counted and used to estimate the total number of fruits consumed per scat. Mammals were classified to species level when teeth were found in the faecal samples, using reference keys (Yalden and Morris 1990; Corbet and Harris 1991). Beetles and other insects were grouped into broad categories.

Dietary composition based on percentage mass ingested

To estimate the relative biomass of each prey group, two separate methods were used. Where counts of prey items could be estimated (i.e. earthworms, fruits, wheat), the number estimated for each scat was multiplied by the live/fresh weight of that prey type to obtain the biomass consumed. Due to the inconsistency of weights for Lumbricus species in previous studies (e.g. Kruuk 1978a; Kruuk and Parish 1981; Höfer 1988), and the assumption that L. terrestris may not be the only earthworm species consumed by badgers, the estimated weight of one worm was derived from Kruuk and Parish (1981) using data collected from Monymusk, Scotland, which was considered to be most similar in habitat composition to Dalby (Table 6). The relative proportions and mean weights of each earthworm species extracted by formalin sampling from Monymusk were used to determine the “average” weight of an earthworm potentially available for consumption by badgers. Values derived from sampling pasture were used as opposed to conifer woodland, as very few worms were extracted from the latter habitat by Kruuk and Parish (1981) (1.0 L. rubellus per square metre). Mean fresh weights of fruits and wheat husks were derived from samples collected in the field. For all other prey items, the content of each within the scats was translated into biomass of food based on coefficients of digestibility, i.e. the ratio of fresh weight of a given prey item to the dry weight of the remains of that prey item in the scats. Coefficients of digestibility for medium-sized carnivores (Table 7) were taken from previous studies, using values derived for badgers where possible (Goszczyñski et al. 2000) or foxes (Goszczyñski 1974; Frank 1979; Reynolds and Tapper 1995).

Table 6 Estimated weight of one earthworm derived from Kruuk and Parish (1981)

Table 7 Coefficients of digestibility (C _d) used to estimate the total prey biomass consumed by Dalby badgers, derived from previous studies