Geographic, ontogenetic, and intersexual intraspecific variations in the feeding ecology of Vipera ammodytes

While data on the diet of Vipera ammodytes are abundant, most studies are either based on a small number of observations or simply summarize the available information on the species' food spectrum, and only a few provide more detailed analyses. Its diet varies depending on regional characteristics and prey availability; however, data comparing the dietary habits of different evolutionary lineages are lacking. Detailed studies on the ontogenetic and intersexual variations of V. ammodytes feeding frequencies and feeding periods, and their effects on the seasonal fluctuations of vipers’ body condition are also very scarce. To assess poorly studied aspects of V. ammodytes feeding ecology, we investigated different populations in western Bulgaria between 2013 and 2020. There were clear ontogenetic and intersexual variations in the diet of V. ammodytes; however, their patterns differed between the distinct clades, reflecting local geographical characteristics in prey availability. There were also ontogenetic and intersexual differences in feeding frequency and feeding duration. Immature vipers fed more frequently and had a longer feeding period than adults, while adult females had higher feeding frequencies and longer feeding periods than males. These differences affected the overall seasonal fluctuations in vipers’ body condition. The intersexual variations in the feeding ecology of V. ammodytes might be due to differences in energetic demands resulting from the distinct reproductive outputs of males and females. The ontogenetic dietary variations appear to be due to the limitations imposed by the smaller size of immature vipers. At the same time, the high feeding frequencies and prolonged feeding periods of the latter might help them grow faster, thereby either reaching sexual maturity sooner or becoming less vulnerable to predators. We also discuss ophiophagy in V. ammodytes.