Foraging Behavior of American White Pelicans \u3cem\u3ePelecanus erythrorhyncos\u3c/em\u3e

Foraging behavior by American White Pelicans (Pelecanus erythrorhyncos was studied in the Lahontan Basin in western Nevada. Pelicans engaged in cooperative fish herding and in kleptoparasitism upon Double Crested cormorants (Phalacrocorax auritus). Pelicans in groups of size 2 through 6 caught more fish than single birds. Mean strike number increased initially with increasing flock size but leveled off at a flock size of between 3 and 4. strike efficiency (captures/bird/strike) declined with flock size, reaching an asymptote at a flock size of 4. Analysis of the regurgitate of young birds revealed that the pelicans\u27 primary food source consisted of Carp (Cyprinus carpio) and Tui Chub (Gila bicolor). Analysis of flocks of pelicans arriving and departing from the colony on Anaho Island revealed a peak in total arrivals and departures between 1100 and 1300 hrs. This peak appeared to be constant throughout the season although the total number of birds arriving and departing increased into July. Mean flock size increased from April to July. Thermal flocks departing and arriving at higher altitudes were generally larger than low level counterparts. The evolutionary significance of cooperative foraging is briefly discussed