Grassland heterogeneity moderates thermal extremes for imperiled Greater Prairie-Chickens
Greater Prairie-Chicken (GRPC) populations have declined throughout the Flint Hills region over the past three decades. These declines correspond with large scale shifts in management that have resulted in a homogenization of the landscape. It is likely that this shift in management has influenced GRPC nest and adult survival directly through reduced cover, but the impacts resulting from indirect factors such as alterations to the thermal environment are unknown. We investigated thermal habitat selection by GRPC in the southern Flint Hills at The Nature Conservancy’s ~15,000 ha Tallgrass Prairie Preserve. The Tallgrass Prairie Preserve, unlike most of the Flint Hills, varies the spatial and temporal extent of fire and grazing to create a shifting-mosaic grassland landscape. We compared thermal models created from operative temperature (a measure that combines air temperature and solar radiation) gathered at GRPC locations, sites within 2 m of GRPC locations, and the broader landscape to compare use to availability. Thermal models were created using a combination of operative temperature collected in the field and measures provided by a weather station on site.
Our findings show that heterogeneous grasslands have high thermal variability with operative temperature ranging as much as 23° C across the landscape when air temperatures are > 30° C. In this landscape, GRPC are selecting for nest sites that are as much as 8° C cooler than the surrounding landscape when air temperatures are ≥ 38° C. Furthermore, GRPC are selecting for fine-scale differences in thermal environments as nest sites are nearly 4° C cooler than the area 2 m area surrounding the nest. Variation in grassland structure resulting from the fire-grazing interaction may be important in moderating thermal environments. The mechanisms driving differences in thermal environments and GRPC selection of these sites are not yet fully understood, but this work supports the need for maintaining heterogeneity within grasslands. This work also suggests that heterogeneity could be important for conserving imperiled GRPC populations as climate change forecasts are predicting greater thermal extremes.