Great Basin Naturalist


A rodenticide, zinc phosphide, was applied to remove black-tailed prairie dogs (Cynomys ludovicianus) from 6 ha of a prairie dog colony in southwestern South Dakota. Another adjacent 6 ha was left untreated. The removal experiment was repeated two consecutive years. Contingency table analysis showed that the resultant population was not homogeneous; age classes by sex of the immigrant and resident subpopulations were different (P < 0.01). The ratio of adult females to yearling females was greater among immigrants than among residents (P < 0.03). Female immigrants did not produce young in the treated zone during the year of their arrival. Fewer of these females displayed distended nipples than expected (P < 0.01), indicating that these immigrants did not reproduce during the reproductive season immediately preceding dispersal and suggesting that failure to reproduce may have stimulated dispersal.