Illegal hunting as a major driver of the source-sink dynamics of a reintroduced lynx population in Central Europe

Large carnivores, such as wolves and lynx, are strictly protected by law in most European countries. However, they are still vulnerable due to habitat loss and illegal hunting. The Bohemian Forest Ecosystem lynx population is exemplary as a reintroduced carnivore population in Central Europe. The population expanded rapidly after the reintroduction (phase I) but then declined and stagnated at a low population size (phase II). There is some evidence that illegal hunting might have caused this development, but reliable data on the intensity of illegal hunting is lacking, and hence long-term consequences for the population cannot be assessed. We used a spatially-explicit individual-based dispersal and population model to inversely fit mortality probabilities to long-term monitoring data; the model integrated both chance observations and telemetry data, and discriminated between baseline mortality, road mortality and added unknown mortality. During phase I, the estimated added unknown mortality ranged between 3 and 4%, with an extinction rate < 5%; during phase II, the estimated added unknown mortality reached 15-20%, which would prevent animals from colonizing new habitat patches. The probability of extinction in phase II ranged between 13 and 74%, thereby reaching a tipping point at which the additional unknown mortality of a few animals could drive the population to extinction. However, when we considered the national parks as fully protected, the extinction probability dropped to <1%. Based on our results, we conclude that the added unknown mortality is most likely explained by illegal hunting and therefore the highest priority for the conservation of the lynx population in the Bohemian Forest Ecosystem should be the prevention of illegal hunting in national parks and their immediate surroundings.