Breeding season occupancy of long-billed curlews and sandhill cranes in grazed habitats at Red Rock Lakes National Wildlife Refuge, Montana.

Abstract

Long-billed curlew (Numenius americanus) and sandhill crane (Grus canadensis) are species of concern at state and federal levels. The concern is largely due to declines in population resulting from loss and degradation of wetland and grassland habitats that have reduced the amount of available breeding habitat for both species. Red Rock Lakes National Wildlife Refuge (RRLNWR) in southwestern Montana encompasses one of the largest wetland complexes in the Intermountain West, providing important breeding habitat for cranes and curlews in the region. We explored landscape- and plot-scale drivers of curlew and crane breeding-season occupancy ([psi]) in grazed grassland and wet meadow habitats at RRLNWR. Distance to palustrine emergent marsh was the best landscape-scale predictor of curlew and crane occupancy. Mean breeding season occupancy of curlews across sites was 0.68 (95% CI = 0.39-0.87) and increased with distance from emergent marsh, ranging from 0.37 (95% CI = 0.24-0.52) to 0.80 (95% CI = 0.56-0.93) as distance to emergent marsh went from 64 in to 629 in. Conversely, crane mean breeding season occupancy was 0.38 (95% CI = 0.17-0.64) and decreased as distance from emergent marsh increased, ranging from 0.58 (95% CI = 0.27-0.58) to 0.28 (95% CI = 0.11-0.56) as distance to emergent marsh went from 64 in to 629 m. Plot-scale vegetation characteristics available from a reduced data set indicated curlew occupancy was positively related to the ratio of vegetation 5-15 cm tall to vegetation >15cm (([beta]) over cap =4.92, SE = 2.53).