Reproductive characteristics, diet composition and fat reserves of nose-horned vipers (Vipera ammodytes)

Abstract

Long-term ecological studies are usually both time-consuming and costly, particularly when conducted on species with low detectability, such as vipers. An alternative, non-expensive method for obtaining detailed information about numerous important ecological traits, e.g. size at maturity, reproductive output, diet composition and amount of body reserves, are dissections of museum specimens. We dissected 237 museum specimens (125 males and 112 females of all age classes) of the nose-horned vipers Vipera ammodytes from the central and western regions of the Balkan Peninsula. Their reproductive and digestive systems were examined, and fat stores estimated. Relative testes volumes were significantly higher in adults than in subadults. Also, we found seasonal variation of testes volumes in adult males. Females became mature at around 43.8 cm snout-to-vent length (SVL); 38.1 % of adult females were pregnant (i.e. had developed eggs/embryos, suggesting bi- or even triennial reproduction frequency). The average number of developed eggs/embryos was 9.1 (range 5–17). As expected, there was a positive correlation between maternal body size (SVL) and the number of embryos. The nose-horned vipers fed predominately on lizards (64.7 %) and mammals (31.9 %); only a few remains of different prey were found (birds, snakes and centipedes). Analyses of inter-sexual differences showed that males more frequently consumed lizards than mammals, while in females both types of prey were equally present. A subtle ontogenetic change in diet was recorded, with a shift from lizards towards mammals. Adult individuals had more fat reserves than subadults, but there were no inter-sexual differences, and gravid females had similar amounts of fat reserves as non-gravid individuals. The data about reproductive output and dietary specialisation demonstrate the vulnerability of the species, generally regarded as “quite common” and non-threatened. This study might help in the establishment of future conservation studies, and management of the impacts of anthropogenic factors on populations of V. ammodytes in the central and western Balkans.