Morphological change and fat accumulation in juvenile red foxes (Vulpes vulpes) in the Central Tablelands of New South Wales

Abstract

Juvenile red foxes (Vulpes vulpes) reach sexual maturation within 10 months of parturition. During this time juveniles need to manage their energy reserves to fuel maintenance metabolism, growth and reproduction. To determine juvenile growth rates and body energy reserves, I measured body mass, morphology, and estimated body fat, in free-living red foxes from approximately 8 weeks of age through to 1 year old. Foxes (n = 163) were sampled monthly from August 1995 to July 1996 in the Central Tablelands of New South Wales.

Mean body mass of male and female juvenile foxes was indistinguishable from adult body mass by February, at 16 weeks of age (males 4500 g, females 4200 g). Skeletal measurements of body and forelimb length in both sexes also attained adult proportions by February. Further changes in morphology were minimal in first-year foxes.

Total body fat was estimated indirectly using a kidney fat index. Estimated juvenile body fat remained low and stable (6%) in both sexes from December through March. Male body fat peaked in August (11%) but was low in July during mating and also September and October whilst females were denning. Estimated body fat of females peaked in August–September (13%) but declined sharply in October after parturition. In addition, 73% of first-year females sampled during August–October were either pregnant or had recently given birth.