Niche overlap in sympatric populations of stoats (Mustela erminea) and weasels (M. nivalis) in north-east Scotland
The diet, habitat preferences, and foraging behaviour of stoats and living in an area of farmland near Newburgh, Aberdeenshire were studied over a period of years. Additional information was collected from nearby areas of sand dune and mixed farmland and woodland. The differences in size between the species, and sexual dimorphism9 were assessed by measuring' nine body parameters of 54 stoats and 87 weasels. Trophic niche overlap was assessed quantitatively from an analysis of 301 scat and gut samples. The diets of both sexes of both species were very similar though larger predators tended to take larger prey items more often. Radio-tracking techniques were applied to both species during the last two years of the study, over 1300 hours of field observations being made. Both species hunted in the same areas and no differences in habitat preferences were noted. Niche overlap in habitat utilization was assessed quantitatively for ten farmland vegetation-type classifications. Male weasels were territorial. Territoriality in male stoats was not established. Female stoats had contiguous exclusive home ranges but no territorial defense was observed. Female weasels had non-contiguous home ranges. The home ranges of different sexes and different species overlapped. Home range area was much larger than other published estimates but the area within the minimum convex polygon boundaries that was exploited by the animals was similar to estimates from areas of homogeneous habitat. The abundance and distribution of small mammals were monitored in known steat and weasel hunting areas. Breeding of small rodents ceased between November and March/ April and numbers were very low in some habitats by March. It was concluded that exploitation competition between stoats and weasels for small rodents in spring was very probable but that differences in access to small rodents and the presence of some alternative prey at times of small rodent shortage enabled both species to coexists The possibility of interference interactions occurring was established but thought to be unimportant in maintaining the coexistence of the two species on farmland.