Intrasexual territoriality and the spatial and social behaviour of captive feral ferrets (Mustela furo L., Carnivora: Mustelidae).

Abstract

I observed eight male and five female feral ferrets (Mustela furo) directly and by video camera in a 36 m² outdoor enclosure equipped with six dens and 13 tunnels. Five (Replicate I) and six (Replicate II) social groups were observed at three levels of food availability. I determined their main range and core area sizes, use intensity of dens and core areas, and the extent of spatial and temporal overlap between individuals. I assessed the effect of sex, grouping, density, social status and observation period on these activities. I also determined the effect of food availability on main range and core area sizes, use intensity of the arena, dens and core areas, spatial and temporal overlap and social status. The ferrets were observed in both mating and non-mating periods and these data were compared. I also determined the effect of food availability, mating period, social status, density and group composition on the ferrets' behaviour and daily activity levels.

The spatial patterns observed were consistent with previous studies of free-ranging feral ferrets in New Zealand. Males and female main ranges were similar. Main range size increased with increasing ferret density, and their core area use intensity decreased. Dominant males overlapped more in both space and time with females than did subordinate males. There was less den sharing between members of the same sex than between sexes. These observations are consistent with the hypothesis that intrasexual territoriality occurs among wild ferrets.

When food was restricted, males' main range size and core area use intensity both decreased. Main range and core area overlap reduced but use intensity of the overlapped areas increased. This reduction in main range size at reduced food availability was most evident when ferret density was high. Restricting food also caused the overlap in main range areas of males and females to reduce and their den temporal overlap to increase. However, changes in food availability had no effect on the relationship between spatial activity and ferrets' social status. I concluded that avoidance to reduce intraspecific competition may be the factor that induces increased dispersion of carnivores during periods of food scarcity.

During the mating period both male and female ferrets increased their main ranges and reduced their denning time. Dominant males increased their overlap with females and their exclusion of subordinate males from their main ranges, core areas and dens. During the mating period female spatial behaviour influenced the territorial behaviour of males.

During the non-mating period ferrets spent 86% of their time resting, 6% foraging and 3% vigilant. Dominant males rested more than did subordinate males. Ferrets with food in excess of their maintenance requirement spent more time resting than did ferrets with maintenance food or no food. Females rested less, interacted less and mated more than did males. Dominant males rested less, marked more and mated: more than subordinate male ferrets.

Based on these findings, I propose a model for variation in home range, territoriality and dispersion of solitary, sexually dimorphic carnivores in relation to changes in prey abundance. I predict that for small intrasexual territorial carnivores, males will progressively reduce their home range and reduce their intrasexual territoriality as prey availability increases from a 'low' and a 'high' threshold; between these thresholds females will show little variation in their home range sizes and intrasexual territoriality. Below the low and above the high thresholds, intrasexual territoriality will break down and the spatial structure of the population will be indeterminate.

The hypotheses and predictions raised by this study must be tested with ferrets populations in the field. Nevertheless, according to the predictions of this study predicts that the outcomes of feral ferret control operations in New Zealand will differ depending on the reproductive status of the population. Therefore, control operations could be most effective in the non-mating period when reproductive females are more socially dominant. Finally, I conclude that in order to help in the understanding of the social and behaviour ecology of small carnivores, the described methodology is an effective means of studying in captivity aspects of ferret social organisation and behaviour that would be very difficult to observe in free-ranging animals, provided the findings can be validated by subsequent research on free ranging animals under natural conditions.