ASSATEAGUE — The birth of a new foal on Assateague Island last month is the first of what should be many this year on the barrier island.
In late March, a new foal was born to the herd of wild horses on the Maryland side of the Assateague Island National Seashore. The mare is Mieke’s Noe’lani and the suspected sire is Mr. Frisky Hooves. While public access to the state and national parks is restricted during the current pandemic, life goes on as usual at Assateague for its most famed residents with a veritable baby boom expected.
Each fall, Assateague Island National Seashore biologists conduct pregnancy tests on the mares to predict how many new foals are expected to join the herd in the coming year. The results from the pregnancy tests conducted last November confirmed eight mares on the Maryland side of Assateague were expecting at that time, meaning at least seven more foals are expected this year.
The popular horses on Assateague are wild animals and generally left to the whims of nature. However, in the interest of maintaining a healthy population size, the National Park Service several years ago began a contraceptive program for the mares. In almost each year since, selected mares have been darted with a non-invasive contraceptive called PZP in an effort to maintain the size of the herd on the Maryland side in its manageable threshold. The target range for the horse population on the Maryland side of Assateague is 80-100, and there were times over the years when the population was well north of those numbers.
According to the March census, the number of wild horses in the Maryland herd now stands at 73, with the birth of the new foal and three documented deaths over the winter.
As a result, the National Park Service’s contraceptive program has shifted to an adaptive management phase.
“Eight is the most pregnant mares we’ve had in many years, due to no contraception for the last four years,” Assateague Island National Seashore Chief of Interpretation and Education Liz Davis said. “One mare was contracepted in 2016, but none have been since then. We’re allowing mares to reproduce freely until such time as the population once again reaches the upper end of our goal range of 80-100.”
While it certainly isn’t the most glamorous aspect of managing the famed wild horses on Assateague, biologists each November conduct pregnancy tests on the many mares on the barrier island in an attempt to determine how many new foals might join the herd next year. The biologists follow the mares in the herd essentially waiting for them to defecate. The samples are collected, frozen and sent to a lab to be analyzed to determine how many, if any, of the mares are expecting.
“The contraceptive program is in an adaptive management phase,” she said. “We look at the population dynamics each year and make changes as needed. Precise balancing of mortality and foaling is not possible because the age at death varies greatly for each horse, as does the number of mares that will foal in a given year.”
The wild horses on Assateague are just that and generally left to the whims of nature. However, managing the herd size is in the horses’ best interests and the contraceptive and pregnancy testing programs are not invasive.
“The sole reason for monitoring the population, including documenting births and deaths, is to provide the data we need to support a successful management program,” she said. “We want our management actions to not stress the population any more than absolutely necessary, which includes minimizing the attention to pregnant mares.”