This article first appeared in the September 2004 issue of the San Antonio
Every year about this time Mitchell Lake takes on a sort of Jurassic air, in the late summer sun the drying polders and lush vegetation recall the steaming tropical swamps in the dinosaur books I owned as a kid. Large water birds like cormorants and spoonbills have a decidedly archaic look and, to my mind, a Tyrannosaurus striding along the shore of Basin 3 wouldn't look entirely out of place. In the sky overhead there probably won't be any Pterodactyls, but what you are likely to see might seem equally improbable: a long line of American White Pelicans (Pelecanus erythrorhynchos) hanging gracefully overhead on nine-foot wingspans, among the largest flying creatures of the modern world.
Given their size and appearance, it comes as no surprise somehow that White Pelicans are a long-lived species, often surviving more than ten years in the wild. Generally, pelicans don't begin breeding until their third year, and a few non-breeders will linger at Mitchell Lake all year round.
Although small populations breed on the Gulf Coast of Texas and Mexico, the remainder of the more than forty known breeding colonies are located on large lakes and reservoirs across the northern prairie states and provinces. The largest colony known, located on Chase Lake in North Dakota, annually contains an incredible 30,000 birds, perhaps one quarter of the total White Pelican population.
Upon arrival at their breeding colonies in the spring, pairs of pelicans perform courtship flights over the colony site, a display which is thought to cement the pair bond while also attracting other pelicans to the colony. Most often islands and sandbars are selected as nesting sites, the accumulated dropping of the birds killing off most vegetation originally present. The simple circular nests of scraped earth collected debris are placed on the ground, as many as three eggs may be laid although one or two are more usual. In any case, the largest nestling will persecute any siblings present such that most often only one young survives.
Pelicans feed in a manner reminiscent of baleen whales. The bones of the lower mandible are flexible and bow outwards when the bill is drawn through the water, allowing more than three gallons of water to enter the pouch. The mandible then returns to a more normal configuration, allowing water to escape while retaining prey items. While the Brown Pelican of the coast dives for fish, the White Pelican feeds from the surface, repeatedly dipping the bill beneath the water. Often flocks will fish cooperatively, forming lines to confine prey against the shore. Fish comprise most of the diet, but crayfish and amphibians may be taken as well.
Adults feeding young have been known to fly more than 100 miles to forage, parents alternating days while one remains at the nest. By their fourth week after hatching the growing young leave the nest and gather in groups, first flight occurring around twelve weeks of age. Any number of factors can cause mortality among these young birds and in any given year only about half of the adults will succeed in raising a chick to independence.
In recent years, the West Nile virus has been responsible for the death of thousands of young. Other factors can cause widespread losses, too. This past summer the Chase Lake [ND] colony suffered a total nest failure, all 30,000 adults abandoning the eggs and young. In this case there may have been a failure of the food supply, unseasonably cool temperatures perhaps driving the small schooling fish upon which the pelicans depend into deeper water. A seemingly catastrophic loss, but hope lies in the fact that pelicans commonly live long enough for several nesting attempts.
White Pelicans wander widely after breeding before moving south, groups of birds arriving on the wintering grounds from late summer until late in the year. Part of the population winters on the Pacific Coast from California south. Most, however, move south and east to the Gulf States and Mexico, a few thousand of these birds stopping over every year at Mitchell Lake.
Sources and More Info:
San Antonio Audubon Society, 5150 Broadway
#257, San Antonio, TX 78209-5710, (210)
These pages are Copyright ©2005 San Antonio Audubon Society. Permission is granted to other nonprofit organizations to reprint articles, unless otherwise noted. Reprints must refer to the originating web site or newsletter and give credit to San Antonio Audubon Society and the specific author.