The adult brown pelican is a large dark gray-brown water bird with white about the head and neck. Immatures are gray-brown above and on the neck, with white underparts. Although the Caribbean subspecies resembles the eastern subspecies, the Caribbean brown pelican has a darker non-breeding plumage above the surface. The Caribbean pelican usually also has a darker undersurface plumage during breeding than does the eastern brown pelican. Both subspecies can reach up to 8 pounds and larger individuals have wing spreads of over 7 feet.
Brown pelicans nest in colonies mostly on small coastal islands.
The nests are usually built in mangrove trees of similar size vegetation, but ground nesting may also occur. Ground nests vary from practically nothing to well built nests of sticks, reeds, straws, palmetto leaves, and grasses. Tree nests are made of similar materials, only they are more firmly constructed. The eastern subspecies nests mostly in early spring or summer, although fall and winter nesting have been recorded in some localities. The Caribbean subspecies begins nesting between May and August, but the season is at its peak during September through November.