Caribou balance winter range fidelity and plasticity in response to weather, pregnancy, and summer range conditions

Abstract In variable environments, animals can remain in place and tolerate changes or move to areas with favorable conditions. Species must balance the costs and benefits of site fidelity and behavioral plasticity in acclimating to rapidly changing environments. We investigated winter fidelity and behavioral plasticity of the Teshekpuk Caribou Herd (TCH) in Alaska. Using GPS telemetry data for 192 female Caribou (Rangifer tarandus) from 2004 to 2021, we identified patterns of winter distribution and how they changed compared to reports from 1990 to 2015. We investigated fidelity to wintering areas by comparing observed use of wintering areas with expectations based on area, distance, and sociality. We then examined intrinsic and extrinsic factors correlated with TCH winter distribution patterns using generalized additive mixed models to better understand how resources may influence use of wintering areas for the herd. Caribou used the same 4 wintering areas reported in prior studies, but increased use of the eastern wintering areas recently. TCH Caribou appeared to balance site fidelity and behavioral plasticity. Caribou exhibited some winter fidelity, with reuse of winter areas exceeding expectations, but still often changed wintering areas across years. Distribution among wintering areas varied with both intrinsic and extrinsic factors including summer and fall weather and, to a lesser extent, pregnancy, age, forage condition, and insect harassment. Weather variables had strong effects, with warmer fall air temperatures and lower precipitation corresponding to increased likelihood of animals forgoing migration to the southern mountains and instead overwintering on northern coastal plain tundra. Pregnant Caribou also were more likely to remain on the coastal plain overwinter. The flexibility of Caribou exhibiting both winter fidelity and plasticity may enhance robustness to environmental changes, but increased use of areas near industrial development emphasizes the importance of continued monitoring. Researchers should consider fidelity and behavioral plasticity across scales to inform effective management under changing conditions.