Factors influencing the distribution of American White Pelicans foraging on the Yellowstone River, Yellowstone National Park, USA

The American White Pelican (Pelecanus erythrorhynchos) is a predator on Yellowstone Cutthroat Trout (Oncorhynchus clarki bouvieri) in Yellowstone National Park, Wyoming. This two-year study examined the biotic and abiotic factors that influenced the spatial patterns and temporal trends in pelican foraging on the 25-km segment of the Yellowstone River, immediately downstream from Yellowstone Lake. During May-August, 1994 and 1995, 81% of the 1,581 pelicans counted during 62 searches were between the lake outlet and 6 kin downstream. That river region may provide an efficient foraging site for pelicans because many Yellowstone Cutthroat Trout spawn there and the trout from the lake that spawn in river areas farther downstream pass through the region on both legs of their annual spawning migration. Most temporal variation (54-65%) in pelican abundance within years was explained by multiple linear regression models that had river discharge and the counts of trout or their redds (i.e., spawning "nests") at one or the other of two major spawning areas as predictor variables. This study indicated that American White Pelican foraging on the Yellowstone River was associated, both spatially and temporally, with the spawning-related abundance of Yellowstone Cutthroat Trout in the Yellowstone River.