Data from: Delineating seasonal shifts in Reindeer habitat and diet selection by integrating GPS telemetry and stable Isotope analysis

Seasonal changes shape herbivore behaviour by altering forage availability
and habitat conditions; however, few studies integrate diet and habitat
selection data across temporal scales. This study uses seasonality as a
unifying framework to combine fine-scale GPS-based habitat selection data
with broader-scale dietary information from stable isotope analysis (δ¹³C,
δ¹⁵N) of hairs in semi-domesticated reindeer (Rangifer tarandus tarandus).
Thresholds introduced within this framework detect seasonal shifts in
habitat and diet selection and classify foraging strategies along a
specialist-generalist continuum. Despite individual variability, most
individuals exhibited pronounced seasonal changes between spring/early
summer (SES) and late summer/autumn (LSA), consistent with generalist
foraging strategies. Habitat selection models revealed reduced avoidance
of rugged terrain and increased use of mires and bogs from SES to LSA.
Concurrently, isotopic enrichment and niche expansion reflected a dietary
shift from δ¹⁵N- and δ¹³C-depleted plants (e.g., lichens, shrubs,
deciduous vegetation) to more enriched forage types such as sedges,
grasses, horsetails, and mushrooms. We assessed whether individual-level
shifts in diet and habitat use were linked and found an inverse
correlation between the shifts in terrain ruggedness avoidance and dietary
change in approximately 67 % of individuals, suggesting that behavioural
flexibility facilitates seasonal transitions. By integrating spatial and
isotopic data, this study overcomes the limitations of single-method
approaches and provides a more nuanced understanding of the seasonal
foraging dynamics of a keystone Arctic and boreal ungulate. The findings
highlight the plasticity of reindeer foraging within a variable
environment and suggest a capacity to respond to environmental changes.
This framework also offers broader applications for investigating
behavioural responses and ecological strategies in other herbivores facing
climate-driven habitat shifts.