Evidence of migratory coupling between grey wolves and migratory caribou

Large-scale animal migrations influence population and community dynamics along with ecosystem functioning. The migratory coupling concept posits that movement of migrant prey can lead to large-scale movements of predators. In northern ecosystems, spatial patterns and behavioral responses of grey wolf to spatio-temporal changes in its primary prey distribution, the migratory caribou, remain poorly documented. We used a long-term GPS dataset (2011–2021) of 59 wolves and 431 migratory caribou from the declining Rivière-aux-Feuilles herd (Québec, Canada) to investigate movement patterns and space use of wolves related to caribou seasonal distribution. Wolves home ranges overlapped with areas used by caribou year-round, especially in May and winter. Wolves exhibited 3 annual tactics: sedentary (17%), long-distance migration (>700 km) between wintering areas and the tundra (36%), and a medium-distance migration, stopping their northward movement near the treeline (47%). Migratory wolves started spring migration northward earlier than caribou, intercepting their prey on their way to calving grounds, but departed southward for fall migration later than caribou, tracking them on their way back to wintering areas. Wolves near or overlapping areas used by caribou exhibited lower monthly movement rates compared to wolves located further away. Overlap of home range among wolves was higher during migrations and winter but decreased in summer when wolves rear pups and caribou are dispersed on summer grounds. We provide evidence of migratory coupling between grey wolves and migratory caribou, with most wolves adjusting their space use patterns to match their primary prey distribution. Although predation pressure may affect the dynamics of declining caribou herds, the global decline of that prey may in turn impact predators on the long-term, potentially enhancing intraspecific competition for new resources. Highlighting this migratory coupling is a key step to developing appropriate conservation and management measures for both guilds in the context of large-scale migratory prey decline.

Methods
We collected data on grey wolf movements in northern Québec in the annual range of the Rivière-aux-Feuilles migratory caribou herd (RFH). In February and March of 2011–2019, we captured 59 adult grey wolves within the RFH range from a helicopter and using either a net gun or a tranquilizer dart gun with Telazol (10 mg.kg-1). We equipped grey wolves with GPS collars (Lotek, Vectronic, Telonics) programmed to record a location every 1 to 5 hours depending on the collar model and year. Individual grey wolves monitoring lasted on average 419 + 227 days (mean + SD). We defined each wolf-year as 1 April to 31 March of the following year. We captured caribou in the RFH range between December and March each year as part of the long-term population monitoring conducted by the Ministère de l’Environnement, de la Lutte aux changements climatiques, de la Faune et des Parcs (MELCCFP) and Caribou Ungava. We captured caribou from a helicopter with a net gun and equipped them with GPS collars (Vectronic). GPS collars were set to record a location every 1 to 13 hours. A total of 431 females from the RFH were monitored for 741.5 days on average.

Please, refer to Material and Methods for more details about the data cleaning and processing.