The family Pelecanidae was introduced (as Pelicanea) by the French polymath Constantine Samuel Rafinesque in 1815. Pelicans give their name to the Pelecaniformes, an order which has a varied taxonomic history. Tropicbirds, darters, cormorants, gannets, boobies, and frigatebirds, all traditional members of the order, have since been reclassified: tropicbirds into their own order, Phaethontiformes, and the remainder into the Suliformes. In their place, herons, ibises, spoonbills, the hamerkop, and the shoebill have now been transferred into the Pelecaniformes. Molecular evidence suggests that the shoebill and the hamerkop form a sister group to the pelicans, though some doubt exists as to the exact relationships among the three lineages.
The pelican is the subject of a popular limerick originally composed by Dixon Lanier Merritt in 1910 with several variations by other authors. The original version ran:
Anatomical dissections of two brown pelicans in 1939 showed that pelicans have a network of air sacs under their skin situated across the ventral surface including the throat, breast, and undersides of the wings, as well as having air sacs in their bones. The air sacs are connected to the airways of the respiratory system, and the pelican can keep its air sacs inflated by closing its glottis, but how air sacs are inflated is not clear. The air sacs serve to keep the pelican remarkably buoyant in the water and may also cushion the impact of the pelican's body on the water surface when they dive from flight into water to catch fish. Superficial air sacs may also help to round body contours (especially over the abdomen, where surface protuberances may be caused by viscera changing size and position) to enable the overlying feathers to form more effective heat insulation and also to enable feathers to be held in position for good aerodynamics.
The combined population of brown and Peruvian pelicans is estimated at 650,000 birds, with around 250,000 in the United States and Caribbean, and 400,000 in Peru. The National Audubon Society estimates the global population of the brown pelican at 300,000. Numbers of brown pelican plummeted in the 1950s and 1960s, largely as a consequence of environmental DDT pollution, and the species was listed as endangered in the US in 1970. With restrictions on DDT use in the US from 1972, its population has recovered, and it was delisted in 2009.
DDT pollution in the environment was a major cause of decline of brown pelican populations in North America in the 1950s and 1960s. It entered the oceanic food web, contaminating and accumulating in several species, including one of the pelican's primary food fish – the northern anchovy. Its metabolite DDE is a reproductive toxicant in pelicans and many other birds, causing eggshell thinning and weakening, and consequent breeding failure through the eggs being accidentally crushed by brooding birds. Since an effective ban on the use of DDT was implemented in the US in 1972, the eggshells of breeding brown pelicans there have thickened and their populations have largely recovered.
In the late 1960s, following the major decline in brown pelican numbers in Louisiana from DDT poisoning, 500 pelicans were imported from Florida to augment and re-establish the population; over 300 subsequently died in April and May 1975 from poisoning by the pesticide endrin. About 14,000 pelicans, including 7500 American white pelicans, perished from botulism after eating fish from the Salton Sea in 1990. In 1991, abnormal numbers of brown pelicans and Brandt's cormorants died at Santa Cruz, California, when their food fish (anchovies) were contaminated with neurotoxic domoic acid, produced by the diatom Pseudo-nitzschia.
The great white pelican is the national bird of Romania. The brown pelican is the national bird of three Caribbean countries—Saint Kitts and Nevis, Barbados, and Sint Maarten—and features on their coats of arms. It is also the state bird of the US state of Louisiana, which is known colloquially as the Pelican State; the bird appears on the state flag and state seal. It adorns the seals of Louisiana State University, Tulane University, Louisiana Tech University, the University of Louisiana at Lafayette, Loyola University New Orleans, Southeastern Louisiana University, and Southern University, and is the mascot of the New Orleans Pelicans NBA team, the Lahti Pelicans ice hockey team, Tulane University, and the University of the West Indies. A white pelican logo is used by the Portuguese bank Montepio Geral, and a pelican is depicted on the reverse of the Albanian 1 lek coin, issued in 1996. The name and image were used for Pelican Books, an imprint of nonfiction books published by Penguin Books. The seal of the Packer Collegiate Institute, a pelican feeding her young, has been in use since 1885.
The American white pelican has increased in numbers, with its population estimated at over 157,000 birds in 2005, becoming more numerous east of the continental divide, while declining in the west. However, whether its numbers have been affected by exposure to pesticides is unclear, as it has also lost habitat through wetland drainage and competition with recreational use of lakes and rivers.
As waterbirds that feed on fish, pelicans are highly susceptible to oil spills, both directly by being oiled and by the impact on their food resources. A 2007 report to the California Fish and Game Commission estimated that during the previous 20 years, some 500–1000 brown pelicans had been affected by oil spills in California. A 2011 report by the Center for Biological Diversity, a year after the April 2010 Deepwater Horizon oil spill, said that 932 brown pelicans had been collected after being affected by oiling and estimated that 10 times that number had been harmed as a result of the spill.
In May 2012, hundreds of Peruvian pelicans were reported to have perished in Peru from a combination of starvation and roundworm infestation.