Space use and denning behaviour of wild ferrets (Mustela furo) and cats (Felis catus)

We monitored the behaviour of 62 radio-collared ferrets and 25 radio-collared cats in dry, tussock grassland habitat in New Zealand's South Island. The total home range of adult male ferrets (102 ± 58 ha, mean ± 1 s.d.) was marginally greater than that of females (76 ± 48 ha), and averaged 90 ± 55 ha. Male ferret core ranges (27 ± 15 ha) were larger than those of females (16 ± 8 ha). Adult cat home ranges were similar between sexes, and were larger and more variable than those of ferrets (225 ± 209 ha). Core range size of cats was similar between sexes and averaged 54 ± 24 ha. The upper 95% confidence limits of the mean home range lengths of adult ferrets and cats were 2.7 km and 5.1 km, respectively, indicating the width of buffer zones where predator control should be extended to protect the boundaries of areas targeted for predator control in dry, tussock grasslands. Although core areas were mostly discrete, home ranges were distributed randomly, and animals that shared space neither avoided nor attracted each other. Little evidence of territoriality may be related to high densities of primary prey. Too few cats were monitored to determine territoriality. Ferrets used at least 9.4 ± 3.2 dens, and cats used 11.5 ± 3.0 dens during the study. Although 71% of dens were used only once, some were used up to nine times. Day time resting by ferrets was mostly solitary. If transmission of bovine Tb occurs between adult ferrets, simultaneous sharing of dens during the day is unlikely to be a significant mode of transmission in this habitat. We were unable to determine the extent of den sharing by cats. Cats occupied den sites with more shrubs and rocks compared with ferrets. Predator control stations in dry tussock grassland habitat may therefore be more effective at killing cats than ferrets if placed in shrubby, rocky areas.