Differences in trappability of European badgers Meles meles in three populations in England.
Many ecological studies on M. meles, as well as certain programmes to control bovine tuberculosis, would benefit from a greater understanding of the factors that influence the probability of capturing this animal in cage-traps. The authors investigated some of the factors that could explain differences in trappability between 3 badger populations in England: the high-density protected populations of Wytham Woods (WW) and Woodchester Park (WP), and the low-density culled population of North Nibley (NN). Trappability (the percentage of all individuals known alive that were actually captured) did not differ between sexes or adult age classes, but significant differences were found between cubs and adults, study areas, seasons and years, and various interactions between these variables. Circumstantial evidence suggests that the culling of badgers in NN may have resulted in a decrease of adult trappability in the following year. Adult badgers at WW and WP were significantly more likely to be trapped 0 times ('trap-shy') or all 3 times ('trap-happy') in 1996 than predicted by the estimated capture probabilities under the assumption of equal trappability. WW differed from the other study areas in that trappability of its badgers was positively related to their body weight and its adult badgers were more likely to be trapped than cubs. These differences could be a consequence of differences in trapping procedures that were followed at WW (no prebaiting and fewer traps per badger). Trappability of badgers was not associated with social group size. Although it is difficult to determine precisely the movement and tuberculosis status of badgers based on mark-recapture data, the analyses did not suggest that either variable affected the likelihood of being trapped. Studies that compare demographic, biometric and epidemiological parameters based on data collected from badgers captured at different times or places ought to account for the observed differences in trappability.