ASSATEAGUE — The circle of life is evident again this week at Assateague Island with three aging mares missing and presumed dead, but they are expected to be replaced with a veritable foal boom on the barrier island.
It was good news, bad news this week when Assateague Island National Seashore officials announced the results of the February population census of the island’s most famed wild residents. The census revealed three aging mares, Bessy Twister, Patty and a third known only as N6H, are missing and presumed dead.
That bad news was tempered by the results of the annual fall pregnancy testing of mares in the wild horse population on the Maryland side of Assateague Island. The results revealed four mares on Assateague, including Gokey Go Bones, Ms. Macky, Annie Laurie and Susi Sole, tested positive and are expected to produce foals in the coming months. One the positive tests, Susi Sole, actually birthed her foal in January in what was a midwinter surprise.
Historically, new foals on Assateague are birthed most often in the spring and summer, although the pregnancy testing does not predict due dates. Instead, the pregnancy testing only indicates four mares in this case were at least three months pregnant when the samples were taken.
With the presumed loss of the three older mares, the total population of the Maryland herd now stands at 76, which is the lowest number in recent memory.
According to the February census, the size of the herd now stands at 76 including 21 stallions and 55 mares. The ideal target range for the population is 80-100 and with at least three more foals expected this year, the total should come right back to the front edge of that target range.
Three new foals were born on the island last year, but there were also some losses in the population due to old age, illness and vehicle collisions. It’s a pattern that has repeated most recently with the losses of old horses offset by the births of an in-kind number of new foals.
Each November, Assateague Island National Seashore biologists conduct pregnancy tests on the mares among the population of wild horses on the barrier island in an attempt to predict how many, if any, new foals are expected to join the herd in the coming year. Essentially, staffers follow the mares and wait for them to defecate. Samples are collected, frozen and sent to a lab to be analyzed to determine if any of the mares will be expecting next spring.
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 injected, or darted more appropriately, 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.
After years of trending above the ideal population range, a combination of natural losses, attrition, old age and some accidents has brought the number of wild horses on the barrier island down to the low end. As a result, in recent years National Park Service staffers have moved from a reduction strategy with the contraceptive program to an adaptive management strategy.
No mares were darted with contraceptives last year and, as a result, four new foals are expected this year including one birthed in January.