A Field Trial Evaluating Bait Uptake by an Urban Fox (Vulpes vulpes) Population

Abstract

SUMMARY (1) Field trials to evaluate bait uptake by urban foxes were performed in three areas in Bristol, U.K. Seasonal uptake was investigated by laying and monitoring uptake of bait at 2-month intervals throughout the year in the principal experimental area. A biomarker (iophenoxic acid) was incorporated in one of the summer and one of the winter trials, and subsequently foxes were captured in that area to examine for elevated levels of protein-bound iodine in the blood. Bait uptake at different bait densities per fox was investigated in the other two areas. (2) There was a steady increase in the proportion of baits investigated and taken from January/February to September/October, with a slight decrease at the end of the year. There was considerable variation in the proportion of baits taken in different habitat types. Of the foxes sampled, in the summer 35% of adults and 17% of cubs, and in the winter 29% of adults and 23% of sub-adults, were positive for the biomarker. When the number of baits available per fox was doubled, the rate of bait uptake per fox increased in the same proportion. (3) The results obtained were compared with bait uptake from rural foxes in Europe and North America. Bait uptake in Bristol was generally lower than in other studies, as was the proportion of biomarked individuals. The differences in bait uptake in Bristol, throughout the season and at different bait densities per fox, are discussed in relation to fox foraging behaviour and ecology. Mathematical models predict that at least 75% control levels are necessary to prevent rabies outbreaks from spreading, with even higher levels of control needed in some urban areas, and the results presented here show that a control strategy based on a baiting campaign using the protocol currently favoured in Britain is unlikely to reach a large enough proportion of the fox population to control a rabies outbreak.