Nearest-Neighbor Distances Change Over Short Time Intervals in Foraging Flocks of Shorebirds

Abstract An important property of a foraging group is its density, particularly measured as nearest-neighbor distance. This study examined whether distance to the nearest neighbor changes over short time intervals in two fast-moving foragers, Dunlin Calidris alpina and Semipalmated Sandpiper C. pusilla, while at a spring stopover site in Delaware Bay, USA. For 181 focal individuals, nearest-neighbor distance was recorded in 5-s intervals for 60 seconds. For each focal individual, measured values were compared with those recorded at the beginning and end of observations, with the mean of values recorded at the beginning and end of observations, and with the mean of values recorded at the beginning, middle and end of observations. The results of this study indicate that single-point estimates of nearest-neighbor distance may not be appropriate in fast-moving foragers such as sandpipers.