Seasonal changes in plasma testosterone, thyroxine, and cortisol levels in wild rabbits (Oryctolagus cuniculus algirus) of Zembra island

Abstract

Annual variations in testosterone, thyroxine, and cortisol concentrations were recorded in plasma samples obtained monthly from male wild rabbits living in their natural biotope. For comparison, a group of animals was held in semicaptivity close to Tunis. Zembra is an uninhabited, hardly accessible island, north of the bay of Tunis and is a part of a large, protected zone of natural reserve. Warrens of Zembra appear to subsist from a very remote past, without any contact with other strains. In both natural and captive environments, testosterone levels peak sharply in October, decline in November-December, and are low from January to September. Thyroxine titers also peak in October but a second peak occurs in spring, the magnitude of which is markedly higher in natural than in captive conditions. As to cortisol, netting in Zembra results in stress-induced high values but semicaptive specimens exhibit a clear-cut annual rhythm peaking in January.