Suitability of GPS telemetry for studying the predation of Eurasian lynx on small- and medium-sized prey animals in the Northwestern Swiss Alps

Predator diet composition and kill rates have to be known in order to quantify predation pressure on prey populations. While ground-truthing of GPS location clusters (GLCs) is a reliable method for finding large- and medium-sized prey items, finding the remains of small prey is still considered a major difficulty. In this study, we searched GLCs of Eurasian lynx Lynx lynx in the Northwestern Swiss Alps in order to determine if GLC analysis is a suitable method for detecting kill sites of new-born ungulates and other small prey animals. Juvenile ungulates made up 26% of the prey spectrum and 17% total consumed biomass (TCB), while hares, marmots, and red foxes accounted for 25% of all found prey items (8% TCB). Lynx spent significantly more time in GLCs containing large prey, but no clear transition in GLC duration for distinguishing between large (≥ 10 kg; mean duration = 46.9 h, SD = 30.1 h) and small prey (< 10 kg; mean duration = 26.7 h, SD = 21.1 h) could be defined. We explored the influence of different cut-off values for GLC duration on lynx diet composition. GLCs with a duration of < 9 h had less than 25% detection success, but still contained 13% of all small prey items. We conclude that GLC analysis is a promising tool for exploring predation on new-born ungulates, mesopredators, and other smaller prey animals weighing between 2 and 10 kg. However, substantial field effort is mandatory to sufficiently detect prey remains in short-lasting GLCs.