The Endangered Species Act was passed by congress on Dec. 28, 1973, which means Saturday marks its 40th anniversary, Tri State Neighbor reported.

Under its bipartisan legislation, thirty one species, including bald eagles, eastern sea lions, American alligators, Lake Erie water snakes, and Virginia flying squirrels have regained their numbers and over 2,000 have benefited from its protection, according to Tri State.

As one of the act's executors (along with the Commerce Department's National Marine Fisheries Service), the U.S. Fish and Wildlife Services (FWS) published several features this week in honor of the ESA going over the (ant) hill. A few interesting historical facts are highlighted below.

The first endangered species legislation dates back to 1900 over concerns of the diminishing passenger pigeon population, according to the FWS website. (Unfortunately, they went extinct in 1914 because of hunting and habitat destruction.) In 1903, noted animal lover Teddy Roosevelt helped create the first Federal Bird Reservation, established on Pelican Island, Florida.

Acts designed mostly to protect birds and Rachel Carson's "Silent Spring" dominated the movement for the next fifty years or so until the federal governments passed its first law, the Endangered Species Preservation Act of 1966. Its inaugural group of species included the Timber Wolf (populations successfully restored in Minnesota and Michigan by 2007), Florida Panther (still endangered), Grizzly Bear, Indian Bat, and 10 other mammals, 36 birds, 3 reptiles, 3 amphibians, and 22 species of fish, according to fws.gov.

The 1966 act would be amended several times before the ESA was signed by Richard Nixon into law in 1973. Over the years, invertebrates (such as clams and insects) and plants would fall under its protection. In 1985, the brown pelican became the first species to be taken off the list for showing substantial recovery. The American alligator was delisted two years later. In 1989, the act extended its influence overseas by banning the trade of ivory.