Old yet useful: VHF and GPS datasets to evaluate climate- and human-driven space use shifts in a large herbivore over decades

Early radio-telemetry methodologies have been surpassed by the more efficient and precise GPS technology in tracking animal movement. However, ‘old’ datasets may spur renewed interest in scientific analyses addressing middle to long-term questions, such as population distribution shifts. Climate trends can normally be tracked in the time scale of several decades, or centuries. However, evidence of temperature global increase requires urgent assessments of responses at different ecosystem levels. We used a contemporary dataset of GPS locations (2012-2015) and an historical one of VHF locations (1997 – 2002) of a large herbivore (roe deer Capreolus capreolus) in an Alpine ecosystem to evaluate the effects of winter weather variability on its spatial distribution over decades. We hypothesized that the upwards migration of the snow-line in the Alps and the increased availability of supplemental feeding led to significant shifts in roe deer space use patterns. Our analysis built upon a resource selection function (RSF) predicting habitat selection as a function of snow depth, canopy cover, and supplemental feeding in both periods. We then evaluated changes in roe deer habitat selection between (“inter-period”) and within (“intra-period”) the two study periods, by means of kappa statistics. We found that changes in habitat selection during the historical intra-period were significantly less than those of the inter-decadal period and of the central months of the contemporary intra-period. Also, contemporary intra-period changes in habitat selection were significantly more than those of the inter-decadal period, but not in December and April. Our results suggest that habitat selection variability by roe deer increased over decades, with more variable snow depth and increased supplemental feeding practice. Animals proximately respond to environmental variability through movement, hence studies across decades may track climatic change and variability.