Assateague Island, a long barrier island straddling the coastlines of Maryland and Virginia, is known for its population of wild horses, often referred to as Assateague’s ponies. These equines roam the beaches, dunes, and salt marshes. The specific number of horses is not static but is an actively managed total, split into two separate herds with distinct administrative oversight. This article details the current population and the unique contexts that govern their existence.
The Dual Herds and Official Counts
The total horse population is divided into two distinct herds, separated by a fence at the Maryland-Virginia state line. Because the two herds are managed under fundamentally different philosophies, there is no single, fixed census number for the entire island.
The Maryland herd, managed by the National Park Service (NPS), operates under a population goal of 80 to 100 individuals. This range ensures the health of the horses and the island’s fragile ecosystem. The most recent census conducted in March 2025 placed the Maryland herd count at 79 horses, keeping it within the desired range.
The Virginia herd is owned and managed by the Chincoteague Volunteer Fire Company (CVFC). They maintain the animals on the Chincoteague National Wildlife Refuge under a special grazing permit from the U.S. Fish and Wildlife Service (USFWS). This permit restricts the Virginia herd to approximately 150 adult animals. The horses are called “ponies” due to their smaller, stocky stature, a physical adaptation to the island’s harsh environment. The total adult population consistently hovers around 230 to 250 individuals, though this number temporarily swells with new foals each spring.
Historical Theories of the Ponies’ Arrival
The presence of horses on this remote barrier island gives rise to two primary theories concerning their origin. The popular local story suggests the horses are descendants of survivors from a Spanish galleon that wrecked off the coast in the 17th century. The narrative suggests the horses swam ashore and established the wild population. This theory has gained modern credence with genetic evidence showing a close relationship between the Assateague ponies and the Iberian horses brought to the Americas by Spanish explorers.
The more commonly accepted historical theory, supported by the National Park Service, suggests the horses arrived during the colonial era. Settlers in the 17th century transported their livestock to barrier islands like Assateague to avoid mainland fencing laws and taxes. These domesticated horses were left to graze freely and eventually reverted to a feral state. They adapted over centuries to the demanding conditions, thriving on a diet of salt marsh cordgrass and dune grasses.
Managing the Population Size
The distinct administrative bodies for each herd employ two different methods to maintain their target population numbers. The National Park Service manages the Maryland herd as a wildlife population, using a scientific approach focused on fertility control. This control is achieved by remotely darting the mares with the Porcine Zona Pellucida (PZ-P) immunocontraceptive vaccine.
The PZ-P vaccine stimulates the mare’s immune system to produce antibodies that block the sperm receptor sites on the egg’s outer membrane, preventing fertilization. This method is reversible, non-hormonal, and administered as an annual booster shot. This allows the NPS to precisely control the birth rate and maintain the Maryland herd within the 80 to 100 animal goal.
The Chincoteague Volunteer Fire Company controls the size of the Virginia herd through the annual “Pony Penning” event held in late July. During this event, the horses are rounded up and swum across the channel to Chincoteague Island, where most of the foals are auctioned off. This yearly auction maintains the mandated herd size of 150 adult animals and provides a significant source of revenue for the volunteer fire company.