Climate change-induced shifts in survival and size of the worlds’ northernmost oviparous snake: a 68-year study

Because of their dependence on ambient temperature ectothermic animals can
serve as sentinels of conservation problems related to global warming.
Reptiles in temperate areas are especially well suited to study such
effects, as their annual and daily activity patterns directly depend on
ambient temperature. This study is based on annual data spanning 68 years
from a fringe population of Grass Snakes (Natrix natrix), which is the
world’s northernmost oviparous (egg-laying) reptile, and known to be
constrained by temperature for reproduction, morphology, and behavior.
Mark-recapture analyses showed that survival probability was generally
higher in males than in females and that it increased with body length.
Body condition (scaled mass index) and body length increased over time,
indicative of a longer annual activity period. Monthly survival was
generally higher during winter (i.e., hibernation) than over the summer
season. Summer survival increased over time, whilst winter survival
decreased, especially during recent decades. Winter survival was lower
when annual maximum snow depth was less than 15 cm, implying a negative
effect of milder winters with less insulating snow cover. Our study
demonstrates long-term shifts in body length, body condition and seasonal
survival associated with a warming climate. Although the seasonal changes
in survival ran in opposite directions and though changes were small in
absolute terms, the trends did not cancel out, but total annual survival
decreased. We conclude that effects of a warming climate can be diverse
and pose a threat to thermophilic species in temperate regions and that
future studies should consider survival change by season, preferably in a
long-term approach.