Large populations of birds inhabit the island, including
American oystercatcher,
great blue heron, and
snowy egret. There are over 320 species that are known to inhabit the island during some portion of the year. These include gulls, terns, and other shorebirds along with raptors, waterbirds, and waterfowl. The
piping plover is a
threatened species that nests on Assateague. The
feral horse population of Assateague Island is alternately known as the Assateague horse in Maryland and the
Chincoteague pony in Virginia. This distinction, made both on per-breed and per-individual basis, is sometimes a matter of disagreement. The traditional definition of a horse or a pony is based on whether the animal in question falls over or under . The equines on the island tend to be under 14.2, but have a horse
phenotype. It is argued that their relatively small size is primarily due to environmental, rather than genetic conditions. The National Park Service provides information about these animals through brochures and the internet. The Maryland and Virginia horses are kept apart by fencing at the border between the two states. Though commonly called "wild," these horses had domesticated ancestors. Legend states their ancestors were survivors of a Spanish galleon that shipwrecked along the coast, and DNA evidence indicates the modern population includes the closest living descendants of Spanish horses brought to the Americas in the early 1500s. Previously, it was suggested the horses originated from late 17th century mainland owners who brought their horses to the barrier islands to avoid fencing laws and taxation. In Virginia, the Pony Penning Days auction keeps the horse population at levels required by agreement with the Chincoteague National Wildlife Refuge. ==Climate==