'Non-Breeders' in the Red Fox Vulpes vulpes: A Case of Resource Surplus

Abstract

During a seven year study in southern Sweden the spring density of red fox Vulpes vulpes remained fairly stable, although its main prey, rabbits, changed markedly in density between years. When rabbits were most abundant, probably more than one female in each fox group bred. Competition between breeding females within the groups lowered the foxes' reproductive success when the rabbit density began to decrease. From the second year of rabbit decline, only one female per group bred, and approximately half of the group members (and the population) were non-breeders, presumably mainly females. The rabbit density was exceptionally low in the last two years of the study (1980 and 1981). In 1980, when non-breeders still were present, the foxes' reproductive success was low. Although the rabbit density in spring 1981 equalled that in 1980 the number of foxes had dropped and few nonbreeders were present. Yet, the production of fox cubs was considerably larger in 1981 than in 1980. I therefore question if the non-breeders in this population really help the breeders in their reproductive effort. Instead I suggest that the evolution of kinship-groups in the red fox is induced by a temporary resource surplus within the territories.