1. Foxes Vulpes vulpes probably did not occur naturally on the Isle of Man, but were present in small numbers in the mid 19th century. They were introduced again in the 1980s, and in 1990 the population was estimated at 120–300 individuals (20–50 per 100 km2) on the basis of field signs. We used a nocturnal spotlight transect survey technique to assess the status of foxes on the Isle of Man in September 1999. This method had previously been used effectively to estimate fox densities in populations as sparse as 16 per 100 km2. We surveyed a total of 852 km over a period of eight consecutive nights, during weather conditions which allowed excellent visibility. No foxes were seen.
2. By comparison with equivalent survey efforts in reference areas of mainland Britain, we conclude that post-breeding fox density on the Isle of Man was certainly below 2.5 per 100 km2, implying a maximum of 15 foxes on the entire island. We estimate a probability of only 15–25% that a fox population of 1 per 100 km2 was present but not detected; this would be equivalent to only five or six individuals on the whole island. Foxes may even be entirely absent, although unsubstantiated sightings continue to be reported.
3. This finding is significant in understanding the ecology of the Isle of Man, and in planning the conservation of a number of ground-nesting bird species there, as well as for farming interests, and for contingency planning against an accidental introduction of rabies.