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Pelicans are believed to breed at three years of age. The breeding period typically is mid-April through mid-September. Nest building takes 3 to 5 days after the onset of courting. Egg laying begins about 4 to 5 days after nest site selection, with an interval of 2 days between eggs. They have one clutch of 2 eggs per year. Smaller clutches often are due to egg loss due to predation. Due to asynchronous hatching and siblicide (one young bird kills the other), only one young typically survives to fledging. Average documented nest success ranges from 0.34 to 0.89 young fledged per nest. It is not known if pelicans renest following the loss of a clutch early in the season.
Eggs hatch approximately 30 days after being laid and the chicks fledge approximately 10 weeks later. Both sexes attend the nest and young.
American white pelicans are ground nesters and prefer remote, isolated islands for colony sites. These breeding sites vary from nearly barren to densely vegetated, but are usually near water. Nests are typically shallow depressions on the ground with a small raised edge made from the adult raking gravel, soil, or vegetation with its bill.
American white pelicans forage during both the day and the night. However, pelicans in south Louisiana and northwest Mississippi forage primarily during the morning and afternoon. Pelicans feed singly, in small groups (two to 25 birds), or in large groups of more than 25 birds. When foraging singly or in small groups, pelicans usually dip their bills to search for food as they swim. When cooperatively foraging, pelicans herd their prey toward shallow water by swimming side by side and synchronously dipping their bills. Pelicans have been known to fly up to 190 miles from a breeding colony to a feeding site and prefer to forage in shallow water. Catfish ponds provide a nearly perfect foraging environment for pelicans, due to the relatively shallow pond depth (approximately five feet) and high fish stocking densities.
In one study conducted in south Louisiana and northwest Mississippi, researchers found that pelicans at catfish ponds spent about 4% of their day foraging and 96% loafing, whereas pelicans foraging in other habitats (crawfish ponds, rivers, lakes, and bayous) spent about 28% of their day foraging and 72% loafing.
American White Pelicans are cooperative foragers. They often forage in large groups using synchronized movements to herd and capture prey (e.g., swim in a line and synchronously dip their bills). Pelicans use air temperature thermals during flight to reduce their energy expenditure. Birds flap and circle to gain altitude in a thermal. Then they release from the thermal and glide long distances, repeating the process until they arrive at their destination.
Pelicans generally arrive at their breeding colonies during April to May and remain through early to mid-September. Fall migration usually takes place from mid-September through mid-November. Pelicans occupy their wintering areas from mid-November through the end of February. Spring migration typically takes place March to April.
Pelicans breed and spend the summer months on remote islands of freshwater lakes and forage in lakes, rivers, marshes, and aquaculture facilities year round. Pelican mean home ranges vary from 110 to 2,927 square miles in the summer and from 115 to 569 square miles in the winter.
During migration, pelicans typically fly along river corridors and valleys but do cross deserts and mountains. Pelicans often stop over at waterbodies that provide forage and loafing sites. Pelicans readily take advantage of aquaculture sites during migration and on their wintering grounds. While on their wintering grounds pelicans use sand bars, mud flats, flooded agriculture fields, and abandoned fish ponds as loafing sites.
Pelicans prefer to forage in shallow water (1 to 9.8 feet) in open areas of marshes, lakes, rivers, ponds, but are also known to forage in deeper water to take advantage of prey driven to shallower depths by diving birds such as cormorants. Pelicans are tip-up foragers; they do not submerge or dive. A pelican cannot forage deeper than it can extend its neck, head, and bill. A typical pelican can easily reach to 3.3 feet below the surface of the water.
Pelicans typically feed on fish, crawfish, and amphibians, ranging in size from 1.6 to 24.8 inches. To forage, a pelican dips its bill into the water and scoops prey into its gular pouch, then raises its bill above its head to swallow. Pelicans prefer to forage for schooling prey but will forage for dispersed prey. Pelicans forage twice a day, consuming an average of 1.2 pounds per foraging trip. Researchers, however, have recorded a pelican consuming as much as 6.8 pounds in a single foraging event.