Mark-recapture estimates of survival in populations of the asp viper, Vipera aspis aspis

We estimated the annual survivorship of two populations of the asp viper, Vipera aspis aspis, by recapturing known adult individuals in the field over six and nine years respectively. The snakes at the two study sites in the Jura mountains of northwestern Switzerland were active between mid-March and mid-October. Vipera a. aspis is easily captured by hand, has individually recognizable marks and is, therefore, well suited for long-term mark-recapture studies. The maximum likelihood estimates of annual survivorship are about 0.75 in both populations. The probability that a snake will be recaptured in any given year is about 0.4 (habitat A) and about 0.33 (habitat B). Sampling effort within a year had little effect on the probability of recapture. Our best estimate of annual survival of 0.75 for the two habitats combined compares well with other previous estimates in viperids and in V. aspis in particular. We found no detectable differences in the survival rates between sexes even when the two habitats were combined. We found weak evidence that there was a difference in the recapture probability between the sexes. The minimal adequate model for the combined data set suggested that there is a higher probability of recapturing surviving females (0.545) than males (0.331).