Space Use and Diet of Territorial Long-Billed Curlews (Numenius americanus) during the Non-Breeding Season

Abstract

During the non-breeding season, shorebirds concentrate in areas of high prey availability where some individuals defend feeding territories. We examined relationships be- tween diet and variation in home range size (ha), distance moved (m, km), and spatial patterns (uniform, random, aggregated) of long-billed curlews (Numenius americanus) occupying low- tide feeding territories from June 1998 to March 1999. During 2-hr focal observations, sizes of home range (1.3 to 7.5 ha) and total distances moved (1.1 to 2.8 km) differed among curlews. Within home ranges, the spatial distribution of curlew locations (recorded at 2-min intervals) was most often (74%) uniform. Home range sizes differed among territories in summer and winter; distances moved differed among territories in summer but not winter. There was no difference among territories in the spatial pattern of curlew locations. Curlews fed for similar proportions of time in summer (84%) and winter (88%). Summer diets differed because curlews ate many bivalves on 2 of 8 territories; diets also differed in numbers of shrimp, crabs, and worms. During winter, diets were similar among 3 territories. Curlews ate fewer shrimps, crabs, fishes, and other (unknown prey) and more worms in winter than summer. Curlews occupied larger home ranges, moved greater distances, and were more aggregated in their use of space when they fed a greater proportion of the time, and especially when diets consisted of more crabs and fewer bivalves. This variation is probably a result of curlews using visual and tactile cues when foraging for different prey. Space and diet varied among and co-varied within ter- ritories, probably in response to spatial and temporal variation in food distribution and abun- dance, competitor density, and habitat configurations.