Wolf monitoring in France : a dual frame process to survey time- and space-related changes in the population

Abstract

The wolf recovery in France dates back to 1992, following the natural range expansion of the remaining Italian population since the late 1960’s. Facing a high level of interactions between wolves and sheep breeding, decision makers had to quickly balance the need for managing livestock depredations with the conservation of wolves as a protected species. The French authorities therefore required a reliable assessment of changes in the species range and population numbers, as well as a reliable monitoring of depredations on livestock, all being key variables to be further included within the governmental decision making process. Because of their elusive behaviour, high mobility, and territoriality, applying a standard random sampling design to the monitoring of awolf population would lead to almost no chance of collecting any signs of presence. In order to increase detectability, we use a dual frame survey based on two spatial scales (“population range” and “reproductive unit”) investigated sequentially thanks to a network of specifically-trained wolf experts distributed over 80000 km2 to collect the data. First, an extensive sign survey at a large scale provides so-called cross-sectional data (pool of signs from unknown individuals for a given year), thereby allowing the detection of new wolf occurrences, new pack formations, and the documentation of geographical trends. Secondly, an intensive sign survey within each detected wolf territory, based on standard snow tracking and wolf howling playback sessions, provides some yearly updatable proxies of the demographic pattern. The combination with a non invasive molecular tracking provides longitudinal data to develop mark-recapture models and estimate vital rates, population size and growth rate, while accounting for detection probabilities. The latter are used in turn to control for proxies’ reliability and to implement demographic models with local population parameters. Finally, wolf activity patterns in connection with predator-prey dynamics is investigated through a pilot study carried out with both wolves and four ungulate preys radio-collared. A particular attention is paid to checking the reliability of presence sign data, as well as improving the cost-efficiency ratio of the monitoring. Finally, these results are also used by the government as one of the components in the decision making process related to the management of coexistence with wolves