Identification des classes d’âge dans les populations de belettes (Mustela nivalis L. 1766)

Abstract

King (1980) pointed out how imperfect are age determination methods in the Weasel. She argued that these imperfections mainly result from a great interpopulation variability, a strong sexual dimorphism and the population multivoltine dynamics. Because of the difficulties to find out an appropriate individual age determination method, she proposed to develop a strategy allowing to determine the age structure of the population. According to this point of view, we tried to reinforce the consistency, pertinency and generality of Carolyn King’s strategy, using arguments provided by the study of cranium and mandibula’s morphogenesis. Traits of the chronologically well known natural history of the species were put in relation with morphological changes of its cranium and its mandibula ; in this way, we were able to allocate our animals to 4 age classes (0-3 months ; 3-6 months ; 6 months -1 year ; more than one year). A sample of 565 weasels collected sequentialy, during at least 7 months in 3 localities, was apportioned according to this method. The resulting population structure was consistent with that obtained by the use of several morphometric methods. These French data corroborate the existence of a strong sexual dimorphism in this species, and its great variability in stature on a large area. It also provides circumstantial evidence for two reproductive periods during the year. A strategy of sampling and processing of a numerous sample is proposed.