Differential Investment in Mating by Red Foxes

I measured physical condition, body mass, age, and mass of gut contents for 330 red foxes, Vulpes vulpes, in an area of central Italy. Females were fatter than males (P < 0.001), and they were fatter in the southern part of the study area than in the northern part (P < 0.001). Males had the same fat level across the study area (P > 0.887). Large males ate less (P = 0.069) during mating season, and their condition deteriorated immediately afterwards (P < 0.001). Small males maintained their body fat during the breeding season (P = 0.467), even though superficial fat decreased slightly (P = 0.069). Adult males maintained body condition for longer periods and recovered more rapidly than yearlings. Neither mass of gut contents nor body-fat indices varied in the same periods for females (P > 0.125). This pattern of differential inter- and intrasexual investment in mating suggested alternative mating strategies in males. Large males may have spent less time hunting and more time searching for multiple mates and fighting with other males; small males may have saved energy guarding their mates and may not have attempted to mate with additional females. These findings suggest that not all red foxes are monogamous.