Sex- and age-related variations in seasonal and circadian activity of the Nose-horned Viper Vipera ammodytes (Linnaeus, 1758)

Abstract

The seasonal and circadian activity patterns of Vipera ammodytes were studied in five sites in western Bulgaria between 2014 and 2017. Vipera ammodytes was active from the end of February to the first half of November. In spring, adult males emerged a few weeks earlier than females and immature vipers. In autumn, the different sex/age groups started their hibernation approximately at the same time. We registered differences in the seasonal and circadian activities between the different sex/age groups. Adult males and subadults were mostly encountered during spring and autumn, and juveniles mainly in autumn, while the encounter rate of adult females was steady throughout the activity period. Females’ circadian activity varied according to their reproductive status. The observed patterns might be a result of the complex effects of many factors, such as climatic conditions, differences in the reproductive behaviour and the cost of reproduction between sexes, as well as the trade-off between precise thermoregulation, predation risk and foraging needs.