An Estimation of the Number of Foxes (Vulpes vulpes) in the City of Bristol, and Some Possible Factors Affecting Their Distribution

Abstract

In 2 areas of Bristol, one 5.5 km2, the other 3.2 km2, fox litter counts in 2 consecutive years were used to estimate the number of fox family groups. There were 3.64 family groups/km2 in the larger area, 3.13/km2 in the smaller. In parts of the larger area densities of 4-5 family groups/km2 were recorded. To obtain data on the distribution and relative densities of foxes throughout Bristol, nearly 88,000 school children were asked to record fox sightings for a period of 1 mo. Since the absolute fox densities were known for 2 areas, the distribution of recorded sightings could then be used to estimate fox densities throughout the city. By this means it was calculated that there were 211 fox family groups in an area of 116 km2, a mean density of 1.82 fox family groups/km2. Fox distribution in the city was uneven, and fox density was not found to correlate with household density, housing type, age of housing stock, or any other obvious habitat feature. There was a negative correlation (P < 0.001) between the distribution of stray dogs and urban foxes. This was attributed to disturbance of the fox population by stray dogs. Disturbance may be particularly important in the breeding season; dogs were the 2nd major cause of mortality in young fox cubs. Based on post-mortem material, the ratio of breeding to non-breeding vixens was 1:0.35, and so the adult fox population consisted of 211 males, 211 breeding females and 74 barren females. Assuming that all fox family groups breed each year, with a mean birth litter size of 4.80 (calculated from placental scars), the annual cub production would be 1013.