Examining impacts of climate change and habitat loss on the distribution of long-billed curlews, a species at risk in Canada

Climate change and habitat loss are severely impacting wildlife species at a global scale, shifting their distributions and driving population declines. Grassland birds are experiencing the steepest decline of any bird group due to ongoing degradation and loss of grassland habitats. These losses are largely driven by agricultural and urban expansion to feed and house a growing human population. The Long-billed Curlew (Numenius americanus) is an at-risk grassland species that breeds in grassland and agricultural habitats throughout western North America. I investigated recent changes in the distribution of Long-billed Curlews within British Columbia and across their widespread North American breeding range. Additionally, I worked to identify the potential drivers behind observed distribution shifts. British Columbia contains the northern periphery of the Long-billed Curlew’s breeding range and as such, this region makes an excellent case study to understand how habitat loss and climate change are impacting leading-edge grassland bird populations. Using targeted survey data from British Columbia spanning two decades (2000-2002 and 2022- 2023), I asked how changes in land-use and climate have affected Long-billed Curlew distribution and range limits in the province. Furthermore, I developed occupancy models to understand how environmental variables such as habitat type predict Long-billed Curlew occupancy and detection within the province. Taking a range-wide approach, I then used community science data (eBird) to investigate recent (2010-2022) changes to Long-billed Curlew distributions across North America as a whole and within each of the Bird Conservation Regions (groupings of similar bird communities and habitats) within which it occurs. Long-billed Curlews showed an apparent ~177 km northern range expansion in British Columbia between the early 2000s and 2023. Additionally, we uncovered a 228 km northern shift of their population centroid across North America between 2010 and 2022. These findings are consistent with the unprecedented loss and degradation of grassland habitats in southern British Columbia, along with agricultural expansion and a warming climate in northern British Columbia. Eastern and western population centroid shifts were detected in several Bird Conservation Regions, which may be related to local patterns of grassland loss and/or population declines. In British Columbia, curlews were detected at higher frequencies in agricultural lands when compared to grassland and wetland habitats, likely due to the increased availability of agricultural lands in their newly expanded range. Consistent with the above, curlew occupancy was positively associated with agricultural habitats and northern latitudes, and negatively associated with grassland habitats. My results indicate that climate and habitat changes may interact to drive changes in population distributions. On a range-wide scale, it appears that climate change is causing a northward expansion of Long-billed Curlew distribution, but on a local scale, habitat losses and gains may play a stronger role in driving regional distributional changes. My research demonstrates the importance of examining both the regional and range-wide changes to informing effective management of Long-billed Curlews. Future management should focus on restoring grassland habitats through prescribed burns, as well as identifying important grassland regions for Long-billed Curlews and implementing protections for these key areas.