The Wild Mares of Assateague

Nancy Marie Brown
December 01, 1995
2 horses, nose-to-nose, on a beach

Suddenly Paul leaped to his feet. "Look!" he cried as a red streak broke from the herd and went crashing into the woods. "It's the Phantom! I saw the white map on her withers. I did. I did!"

For a full minute the pony was lost among the pines. Then out she came heading toward the White Hills. Behind her whipped the Pied Piper, and his ringing cry was a command. . . . Pied Piper was overtaking the Phantom. He was running alongside her. Now he was twisting into the air, lacing her with his forefeet. They could hear the dull pounding of his hooves aganst her body. Then they saw the Phantom turn. They saw the droop of her tail as she gave up her dash for freedom and meekly followed the stallion into the woods.

Long seconds after they were gone, the air seemed to quiver with the Pied Piper's bugle.

"I hate him!" cried Maureen, bursting into tears. "I hate him! I hate him!"

"Quit acting like a girl, Maureen! Pied Piper knows she's better off with the band. Even the Phantom knows it. Grandpa says horses got to stick together for protection. Same as people."

- from Misty of Chincoteague by Marguerite Henry, 1947

From Tingles Narrows south to the fence at the Maryland-Virginia line, eight bands of wild horses roam the white Assateague sands. They're not the same herds that swim the bay each Pony Penning Day, their foals to be sold off by the Chincoteague, Virginia, Fire Department. Yet they're akin to famous Misty and her mother, the Phantom: They spring from the same stock, descendents of the wreck of a 17th-century Spanish galleon (says one legend) or of a 19th-century tradeship carrying blinded horses destined for deep South American mines. Fat-bellied, big-headed, shaggy-maned ponies, they stand 12 to 13 hands at the shoulder (about 50 inches) and come colored any kind of pinto, pied, skewed, or solid. They organize themselves in the age-old equine way: herds of one stallion with two to nine mares, yearlings, and foals. Bachelor bands of young males form on the fringes, biding time until each can win a herd of his own.

Wild, hemmed in by fence and sea, easy to tell apart, they are perfect animals with which to test our assumptions: In such "harems," as animal behaviorists tag the herds, does male competition alone control who has sex, who sires the generations? Or are we blinded by our metaphor?

3 horses, one head, one butt, one in background. All in high green brush.

"Females are associating in these bands with one stallion," says anthropology graduate student Lisa Ludvico, "but are they mating exclusively with that one stallion?

"I found one mare," she adds, matter-of-fact, "that over a 34-month period visited nine different stallions."

Which is not to say the mare mated with all nine.

"You can't watch all the time," acknowledges Ludvico, whose dissertation research led her to live with the ponies for a year. "It's hard to study large mammals. Horses are a lot more clever than I expected. They could lose me in a second. There's a lot of vegetation, and then they'd swim these guts to these little islands in the bay-" The west shore of Assateague seems to disintegrate into a scatter of spotty islands - all just parts of the "range" to an Assateague mare, but leaving Ludvico on the far shore wishing her offroad pickup would transform into a canoe.

She was never the horsey type. Originally, she had wanted to study primates, her interest in female reproductive strategies being purely anthropological, that is, concerned with how our assumptions about human behavior blur our vision of animals. "But no primates fit the requirements of my hypothesis - that even when males and females are the same size, we assume that the males mate with many, the females only with one."

Horses did fit. "I had made arrangements to work out west, with Joel Berger" - author of Wild Horses of the Great Basin. "Then I found out Ron Keiper was right here." Keiper, a professor of biology at Penn State's Altoona Campus, had been studying the Assateague ponies since 1975 and had, early on, begun poking holes in the harem picture of horse society: He and Katherine Houpt of Cornell had found, for instance, that the stallion was neither the most dominant nor the most aggressive horse in a herd.

In a 1984 Research/Penn State article reporting that work, Keiper had wondered "if we designed that study properly. We counted the number of aggressive acts between adult horses - shouldering another animal aside, threatening to bite, biting, threatening to kick, kicking. The thing we didn't consider is the distance an animal keeps between itself and its nearest neighbor. Often a stallion stays off by himself. When he's got that bubble of space around him, he doesn't have to be aggressive."

Yet other evidence soon confirmed that a stallion was not the sultan of his mares. "When he died, for instance," Keiper says now, "they stayed together."

Ludvico wondered if the mares had more choice in the matter than it might seem. A DNA study of mustang foals, published shortly after she submitted her thesis proposal, convinced her she was on the right track. "They didn't do long-term behavioral studies like I did," she explains. "They came in with a helicopter, rounded up the horses, and found that the stallion they had assumed was dominant in a herd had not sired a third of the foals in his band."

In the spring of 1991, Ludvico moved house to the National Park Service's research station at Tingles Narrows and met her research subjects. They were, she recalls, "real skittish. These are not the horses that will put their heads in your car."

The rest of the year, each day, rain or shine, she picked a herd and watched it for four hours, marking - every five minutes - the distance between individuals ("you do horse lengths, basically, and convert it later") and what each was doing; grazing, biting a fly, rolling in the sand, standing in the waves, fighting.

"Stallions don't have territories," she says, "they have home ranges." The difference is the quality of the defense. "If another stallion comes onto the home range," Ludvico continues, "the home stallion won't leave what he's doing to run him off. Unless he gets too close to the band. Then he'll run up and do some aggressive posturing.

"And 'too close' varies from season to season. In summer, when the insects are biting, I've found three bands less than two feet from each other - one horse after another after another all lined up on the sandbars, out in the water where the flies can't get them. There's hardly room to move out there, much less fight.

"How do I know? I waded out there." (It took her a while to figure out the curve of the bar underwater. The first time she ended up swimming.) "There we were, lined up on the sandbar for four hours: 37 horses and me."

Throughout the year, she also surveyed the vegetation, hoping to gauge the relative desirability of each stallion's home range. "Every third of a kilometer I'd get out of the truck and lay down a transect - a measuring tape, essentially - pull it out 30 meters and see what plants were there. Sometimes there was nothing, sometimes an impenetrable shrub. I haven't finished the analysis yet, but just walking the land, the ranges to the south seemed fantastic - there were really productive little islands of land with lots of grass on them."

Then, in the winter of 1992, she began collecting DNA. "I shot them with a biopsy dart I got from Bill Karesh of the New York Zoological Society." Shaped like a stocky arrow with red plastic fletching, the dart lacks an arrowhead: Instead its cylindrical aluminum shaft is open, leaving a round, sharp mouth; inside are two wire barbs. "It's sharp enough, but it doesn't cause an open wound. The cutting edge cuts a little bit of tissue from the horse, and these barbed brooches hold onto the tissue when the dart pops off the horse." Penn State anthropology professor Henry Harpending, another member of Ludvico's committee, taught her how to shoot. "And the Park Service sent people out with me to make sure I really was a good shot. I had to hit each horse in the rump, the really fleshy part."

She also tried to extract DNA samples from feces ("That's really easy to collect: Just follow them around") and bones. Mitochrondrial-DNA - the single-stranded DNA favored by biologists doing species-to-species comparisons - was readily recovered from feces, but not the undegraded snippets of double-stranded nuclear DNA that she needed to test paternity. (She hopes to continue this work after she finishes her degree.) The bone work was more successful. "I was looking for this one horse, and I couldn't find him. In the spring I got a call from the Park Service saying, 'We've found some bones from him.'" One that she had them send up, an ulna, or front leg bone, is pockmarked with sampling holes. "I've gotten some good DNA out of it," Ludvico says.

In a long, airy room cluttered with beakers and tubes and chemical workstations, Ludvico electrically separates the stallion and foal DNA samples into their component parts, or alleles, and compares the resulting bands, spread out in blue and violet stripes in an agar gel, under ultra-violet light. "It's a test of polymorphism - of difference between individuals. You've heard of DNA fingerprinting? It's like that, but simpler." Certain alleles tagged so that they light up under U-V light are her markers. If enough of the lit-up alleles are found in the same places along the length of the stallion and the foal's DNA bands, then the two horses are related.

If not, the myth of the mighty stud, the sultan of his mares, might have to be rewritten.

"If you go into an animal behavior study with a mindset that says male control," Ludvico says, "you're not going to be looking for female-female interactions."

"Harem," a term liberally applied in animal studies, doesn't seem to fit when the males are no larger, no stronger, and no better equipped than their mates. "With elephant seals," Ludvico says, "you've got a harem. The males are 60 to 80 percent larger than the females. See them together on a beach, and it looks like two different species.

"Or hamadrayas baboons. The males have really big canine teeth, big mantles of fur. And they actually take adolescent females and help rear them until they're mature, then mate with them. That's a classic example of what we think of as a harem organization.

"But horses? They're the same size. Both sexes disperse from their natal band when they're two years old. In the literature, it says that the females leave the natal band, hook up with a stallion, and stay. What I found was that the females move around a lot."

If a mare left her stallion, it was believed, her fertility would decline. "Not true," says Ludvico. For the horses she followed, the single life did not seem to be any more stressful: "Foaling success was not going down," Ludvico says, concluding that "mares don't need the stability of a herd." Nor was the mare harassed by her stallion - as the fictional Phantom was by the Pied Piper - when she left the band to live alone. Not even if she took her offspring with her.

Yet the mares Ludvico watched did seem to prefer the company of their own kin. "Mares associated with their sisters and mothers," she explains, "more than you'd expect them to be doing if it was random: they were together 33 percent of the time."

Could the mares themselves be responsible for the herd? Could their mother-sister group be holding the stallion at bay (Keiper's observed "bubble of space"), permitting him to accompany them, standing by while he fights off male challengers, preferring his home range over another stallion's for its familiarity or the quality of its grazing, but not submitting to the stallion's direction or, necessarily, even mating with him?

Keiper and his colleagues had found that 19 percent of female foals stayed in their father's band instead of dispersing, leading them to draw the conclusion "that inbreeding did occur among wild horses," Keiper notes. "Now Lisa's found that you might stay with your father, but if you have a foal it might not be his," he says.

"There is value in staying with your father," he adds. "You know the home range, you already have a place in the hierarchy." And staying wouldn't harm the genetic fitness of the species, if the stallion does not sire all the foals in his herd - that is, if your "father" is not necessarily the father of your foal. This final question Ludvico's DNA paternity tests will answer.

"This part is the most fun," she says, "but it also took the longest to get to," since to read social structure from a foal's fathering, Ludvico felt she needed to know for certain which stallion was with the herd when the mare conceived. "So I'll find everything out at the end of the study."

Applying for a grant from the National Science Foundation's anthropology section, Ludvico had struggled to keep "Horse" out of her project's title. "They would have put me in biology," she explained, not anthropology.

What she came up with - "Reproductive Strategies of Harem Females" - elicited some snickers and a great deal of prurient interest at the annual Graduate Research Exhibition at Penn State (where she tied for first prize in the Social and Behavioral Sciences category). "People asked me, 'How long did you work for the Sultan?' I hadn't even thought of it that way."

Even the faculty on her doctoral committee occasionally ribbed her as her data accumulated. "My committee's all male," she says, laughing, "and they say, Is this some feminist agenda you've got?"

"Actually, Darwin refers to it." That the males of all mammals eagerly pursue the females is notorious to every one, Darwin wrote in The Descent of Man in 1871. Yet, he continues, the female, though comparatively passive, generally exerts some choice and accepts one male in preference to others. Or she may accept, as appearances would sometimes lead us to believe, not the male which is the most attractive to her, but the one which is the least distasteful. The exertion of some choice on the part of the female seems a law almost as general as the eagerness of the male.

"Why are some birds so brightly colored, Darwin asked? It works against natural selection," Ludvico notes. Yet it may give a bird the advantage, as Darwin put it, in charming the females.

"Everyone jumped on Darwin for the mate choice part," Ludvico continues, "and discounted it until 1971." That year, the book Sexual Selection and The Descent of Man: 1871-1971 was published, a collection of essays by well-known biologists and evolutionary theorists re-examining Darwin's theory. Then, in the early '80s, experiment joined theory, as scientists became able to test the paternity of animals in the field.

Studies on birds, for instance, have shown that "lots of extra-pair copulation is going on," Ludvico notes. "In red deer, they've found some males mating more than they thought." While a 1995 study of gray seals found that the harem leader had sired only 2 pairs of the 48 pairs of pups tested (a pair being pups of the same mother in two consecutive years). "That's what's good about genetic work," says Ludvico, "it's hard data.

"I think the whole focus of my study," she adds, "is to look at female reproductive strategies where you don't expect to find them - where you don't expect it because of the label, harem."

Or, perhaps, because you grew up on the world of horses in Misty of Chincoteague?

"I never read it as a kid," Ludvico laughs. "It was only after I figured out what I was doing for my dissertation that I read Misty. It was a requirement."

Lisa Ludvico expects to receive her Ph.D. in anthropology from the College of the Liberal Arts in 1996; e-mail lul@psu.edu. Her adviser is Henry Harpending, Ph.D., professor of anthropology, 318 Carpenter Building, University Park PA 16802; e-mail hxh5@psu.edu; 814-863-2694. Ronald Keiper, Ph.D., a member of her doctoral committee, is Director of Academic Affairs and Distinguished Professor at Penn State Mont Alto Campus; e-mail rrk1@psu.edu; 717-749-6050. Ludvico's research has received funding from the National Science Foundation, the University's Hill Foundation, Sigma Xi, and the dean of the College of the Liberal Arts.

Last Updated December 01, 1995