The San Francisco Bay Area network of national parks is home to many wading bird species such as the Great Blue Heron (Ardea herodias), the Great Egret (Ardea alba), the Green Heron (Butorides virescens), the Black-crowned Night-Heron (Nycticorax nycticorax), and the Snowy Egret (Egretta thula). In fact, Alcatraz Island in the Golden Gate National Recreation Area is home to one of the largest breeding colonies of Snowy Egrets and Black-crowned Night Herons in the entire San Francisco Bay Area.
Wading birds are carnivorous and spend much of their time in or near fresh or brackish water hunting for small aquatic creatures, and sometimes for small birds and mammals. Many herons and egrets, and most notably the Snowy Egret, were once hunted heavily for their beautiful feathers prompting early US conservation legislation such as the Migratory Bird Treaty Act of 1918. Today wading birds in the United States are coping with different threats such as a 50 percent reduction in wetland habitat and an ever-present risk of poisoning from oil, pesticides or heavy metals.