Built for Speed: a Year in the Life of Pronghorn

Natural History, Nov, 2003 by Laurence A. Marschall

by John A. Byers Harvard University Press, 2003; $24.95

Travelers passing through the Great Plains called pronghorn antelope "prairie ghosts," as a testament to their speed and agility; an adult pronghorn can accelerate from zero to almost sixty miles an hour like a benzene-fueled dragster, and it cruises along effortlessly at forty-five miles an hour, easily outrunning anything that comes after it. Ever since the last lions and cheetahs died out in North America more than 10,000 years ago, there has been no serious predator on the continent that can match the pronghorn for speed. Today's hungry coyotes--the only mammals, other than you-know-who, that effectively hunt pronghorn--can only hope to snatch an occasional fawn in an unguarded moment.

John A. Byers is a field biologist who has spent almost a quarter of a century chasing pronghorn antelopes on Montana's National Bison Range. Byers observes his subjects with such patience that he can recognize individual faces the way most people recognize friends and family. He's read John James Audubon and John Muir, and, as he proves with stirring accounts of his experiences in big-sky country, he can spin a phrase with a skill worthy of those master wordsmiths. But Byers is a hard scientist as well as a lucid writer, and the image of the pronghorn that emerges from his research is not altogether a model of grace and beauty.

If you spied a pronghorn browsing among the summer grasses on the western plains of North America, you'd think they haven't a care in the world. But pronghorns maintain an exceedingly rigid dominance hierarchy that makes everyday life a constant battle. Females, Byers found, expend huge efforts bullying other pronghorns, and much of their time is taken up jostling each other for the choicest napping spots. When one female gets pushed out of her spot by a more dominant individual, she'll wander around looking for an even weaker female to rouse--and so on, until everyone except the weakest has gotten in a lick. Young males challenge equals and inferiors with their horns, playfully at first--then, as they mature and begin to compete for mates, with injurious and even deadly intent.

It's even a bit misleading to describe them as "placidly browsing." Unlike bison or sheep, which simply mow down everything edible in their path, pronghorns are extremely fussy diners. Most of the time they aren't actually eating but nervously nuzzling plants, like a matron at a tea party looking for the choicest nibbles.

And yet, despite their choosiness, I wouldn't want to adopt their nutritional habits. Like cows and camels, they are ruminants, and true prong horn serenity comes from burping up a recent meal, which has been fermenting in an outer stomach, and then chewing it all over and over again for an hour or more. The continuing mastication helps digest the tough material they take in, but it reminds me of one of those stomach-churning ads that run on the seven o'clock news.

What sounds even worse are the special snacks reserved for nursing mothers. After dining on fresh placenta, a pronghorn mom regularly chows down her fawn's feces for several weeks, apparently as a way to manufacture disease-fighting antibodies transmitted to her offspring through the mother's milk. "Natural selection," Byers writes, "can shape the brain to make anything that contributes directly to reproduction feel like fun." Yummy.

The dramatic climax of the pronghorn year, and of the book, is the rut. With winter approaching, pronghorn males each gather small harems of females into gullies and valleys on the prairie, trying to keep them out of sight of their rivals while they woo them. But the females will have none of it. They resist amorous advances time and again. Often, for several weeks, they move from one harem to another, sometimes with a male in pursuit, leaving behind the spilled blood of rejected suitors. Byers's account of one female's experiences is filled with white-knuckle suspense. Which male gets to mate with the lovely pronghorn ingenue? Will she fall in love with Archie's subauricular gland? Will an interloping yearling take her by force before Kareem gets a chance to charm her? It's the pronghorn equivalent of a bodice-ripper, and a natural history lover's delight.

Laurence A. Marschall, author of The Supernova Story, is the W.K.T. Sahm professor of physics at Gettysburg College in Pennsylvania, and director of Project CLEA, which produces widely used simulation software for education in astronomy.