American white pelicans breed on lakes across the Northern Plains and Great Basin of North America. Come autumn, they migrate southward, often using staging areas along the way. Pelicans that breed east of the Rockies generally winter along the Gulf Coast or lower Mississippi Valley while Great Basin pelicans head for the Central Valley of California, the Salton Sea, or coastal bays of Southern California and Mexico. Some permanent, non-migratory colonies inhabit Florida, Texas and Mexico.
American white pelicans are not sexually mature until their third year. Some of the young, non-breeding birds stay on their wintering grounds for the first two years while others migrate northward with the adults. In either case, non-breeding white pelicans tend to wander about during the summer months and may turn up at attractive feeding sites throughout much of the U.S.
Indeed, a flock of American white pelicans has been present at Eagle Bluffs Conservation Area, in Central Missouri, over the past week and, as of this morning, their number had increased to 67. While this summer flock is rather large (based on my experience), the total population of white pelicans has been steadily increasing over the past 50 years due to DDT elimination, hunter education and favorable habitat development (i.e. fish-stocked reservoirs). It is thus likely that summer flocks of these magnificent birds will become increasingly large and widespread in the future (unless global warming decimates their breeding and fishing lakes).