Icing events trigger range displacement in a high-arctic ungulate.

Despite numerous studies of how climate change may affect life history of mammals, few have documented the direct impact of climate on behavior. The Arctic is currently warming, and rain-on-snow and thaw-freeze events leading to ice formation on the ground may increase both in frequency and spatial extent. This is in turn expected to be critical for the winter survival of arctic herbivores. Svalbard reindeer (Rangifer tarandus plathyrynchus) have small home ranges and may therefore be vulnerable to local "locked pasture" events (ice layers limit access to plant forage) due to ground-ice formation. When pastures are "locked," Svalbard reindeer are faced with the decision of staying and live off a diminishing fat store, or trying to escape beyond the unknown spatial borders of the ice. We demonstrate that Svalbard reindeer do the latter, as icing events cause an immediate increase in range displacement between 5-day observations. Population-level responses of previous icing events may therefore not accurately predict future responses if the spatial extent of icing increases. The impact of single events may be more severe if it exceeds the maximum movement distances, so that the spatial displacement strategy reported here no longer buffers climate effects.