Field performance of the M-44 ejector for red fox (Vulpes vulpes) control

Abstract

The M-44 ejector was used to recover red foxes (Vulpes vulpes) in the eastern highlands of Victoria during two summer and two winter trials in 1997–99. Two transects containing 20 devices each were established at five independent sites. Meat baits containing rhodamine B (RB) were used in a three-week free-feeding period at each site before the ejectors were loaded with cyanide capsules and set for a further six weeks. No significant correlation was found between bodyweight and the distance from the bait station that foxes were recovered. No bias was detected in the age of either sex or the overall ratio of males to females. Bait station activity in the free-feed period was not closely correlated with the recovery of foxes at the same bait station. Comparisons with published data found no significant difference in the age structure and sex ratio of foxes recovered with the M-44 and those taken by trapping or day shooting. Nearest-neighbour distances between recovered foxes were significantly smaller in summer 1997/98 than for consecutive periods (P < 0.05). Fox recoveries were contagious in their distribution in all but the winter 1998 period. The age of foxes recovered declined from summer to winter in each year (P < 0.05) and the ratio of yearlings to adults systematically increased over the four periods. Only 39.5% of the 160 foxes recovered overall had consumed a RB-marked bait used in the three-week free-feed period, and 43% of all foxes recovered in the first week were not marked. Over a six-week recovery period in summer 1997/98 and winter 1998 there was a significant inverse relationship between time and the number of foxes recovered (P < 0.05). There was no significant difference in the slopes of the regression describing the recovery of marked and unmarked foxes during summer 1997/98, suggesting that both groups were removed at the same rate. We discuss these data with reference to the use of fox age as an indicator of control performance and suggest a simple strategy to enhance baiting efficacy when fox distribution is contagious.