In late summer, fall, and winter, reservoir levels in the Tennessee River Valley drop drastically as the Tennessee Valley Authority releases water from its series of reservoirs along the river, exposing mudflats that become rich feeding grounds for migrant and wintering birds throughout northern Alabama. When low water levels coincide with shorebird migration, hundreds of shorebirds of various species use this habitat, while wading birds such as herons and egrets hunt frogs, snakes, crayfish, and small fish in the shallow water, and later in the year ducks and gulls also take advantage of the conditions. Longer-legged species such as the Great Blue Heron and Great Egret can forage in deeper water, and Bonaparte's Gulls are frequent visitors in the shallow waters and on the exposed mud. Mudflats also attract many sandpipers, including yellowlegs, dowitchers, and peeps, with the Least Sandpiper noted as the only commonly encountered peep in Alabama with yellow legs, as well as plovers including the Killdeer, Semipalmated Plover, American Golden Plover, and Black-bellied Plover. Because shorebirds migrate great distances, these mudflats can also produce unusual visitors, including the American Avocet, Ruddy Turnstone, and White-rumped Sandpiper.