Unusual Age Structure of the Winter Aggregation of Nyctalus Noctula (Mammalia, Chiroptera) in Kyiv

Abstract

Abstract We analysed the sex and age composition of a large colony of Nyctalus noctula (605 specimens), wintering in Kyiv, Ukraine. Age was identified in 113 individuals using the method of counting growth layer groups in dentine. Males contained ca. 70 % both in the colony and in the sample of animals with the estimated ages. Males and females of all ages were in good body condition. There were bats from 0+ to 7+ years old in the sample. In males, 0+ age class was represented by 38 %; 1+ class, by 20 % of individuals. In females, 0+ and 1+ year old individuals were found in similar numbers: 29 % and 32 % correspondingly. The observed sex ratio and proportions of males and females across age classes cannot be explained only by demography. The data are interpreted in terms of migratory behaviour and mating strategy of the species: the unusual female age structure is possibly due to age-specific preferences in wintering habitat selection and search for potential mating partners.