Prey class selection and kill rates by lynx Lynx lynx were studied in the Swiss Jura Mountains from March 1988 until May 1998 to evaluate the signif- icance of lynx predation for roe deer Capreolus capreolus and chamois Rupi- capra rupicapra. We found clear differences in the kill rates and prey class selec- tion between lynx of different age, sex and breeding status. Male lynx killed more chamois than female lynx, and chamois was never found in kill series of subadult lynx. Family groups had the highest kill rate. They killed an ungu- late every 5.0 days, compared to an average of 6.2-6.6 days for single lynx. During our 10-year study, the density of independent lynx was rather stable, ranging within 0.94-1.01 individuals/100 km2. Based on the observed kill rates and the estimated lynx population structure we calculated that lynx killed 354 ± 13 roe deer and 87 ± 13 chamois annually in the 710 km2 study area. The magnitude of lynx predation on roe deer and chamois was primarily shaped by the lynx population structure. A decline in the number of resident male lynx reduced the number of chamois killed in the study area by 3 of the previous number due to the difference in prey selection of male and female lynx. There was a differ- ence in the most frequently killed age and sex classes between roe deer and cham- ois: lynx killed more male chamois (39%) than females or fawns, whereas in roe deer, does (38%) were most often killed. By altering adult survival, lynx preda- tion has a significant impact on prey population dynamics. Lynx killed a maxi- mum of 9% of the roe deer and 11% of the chamois spring population. Consid- ering the differences in the recruitment potential of the two prey species, lynx has a greater impact on chamois than on roe deer.