Demographic patterns and habitat associations of non-breeding Northern Shrikes ( Lanius borealis ) in Minnesota

Despite its ecological importance as a predatory passerine, the Northern Shrike (Lanius borealis) remains severely understudied. In North America, this species breeds in the boreal taiga and taiga-tundra ecotone and winters across much of the northern continental United States and southern Canada. Because of its remote breeding range, population estimation for this species is challenging, and little is known about its population structure, movement, or habitat use. However, wintering populations in Minnesota provide a unique opportunity to study Northern Shrikes’ non-breeding ecology, as the birds are more accessible, and their habitat preferences are easier to observe during this time. To fill these gaps in knowledge, we (1) analyzed morphometric and demographic data on Northern Shrikes (n = 58) banded in northeastern Minnesota between 2021 and 2024, (2) deployed light-level geolocators (n = 31) on non-breeding Northern Shrikes between 2021 and 2022, and (3) identified land cover preferences throughout Minnesota based on 1185 Northern Shrike eBird observations. We found a significantly higher number of adults present during the winter. Adult males averaged significantly larger than adult females by wing chord and tail length, and adults were significantly longer winged than juveniles. A combination of poor non-breeding site fidelity and near-zero recapture rates prevented the recovery of any geolocator units. Using resource selection functions, we identified that Northern Shrikes used grassland, water, wetland, and developed land in greater proportion to what was available on the landscape, but selected against cropland and forest. Northern Shrikes also preferentially selected for areas with a greater number of land cover types present, indicating a potential preference for heterogeneous landscapes. Our results provide the first description of Northern Shrike demographics, tracking technology deployment, and large-scale non-breeding habitat associations for this species in Minnesota.