These are pronghorn antelope:
But they aren't actually antelope like the ones in Africa
(Antilopinae). Pronghorn are all by themselves in their own taxonomic family of American
antelope (Antilocapridae), roaming the sage flats around the Wild West,
including here in Grand Teton National Park. They used to have about 12 other
brother and sister species (some the size of small rabbits!), which, for
whatever reason, didn’t have the evolutionary edge to survive the last two ice
ages. The lone surviving species, however, is probably the park’s most spectacular
example of adaptive success.
Most animals exist in constant stress with not enough food.
Imagine being a ground squirrel in this ecosystem. Your preferred plant food is
only available for a few short months, and everything is trying to eat you: wolves,
bears, cougars, bobcats, hawks, falcons, badgers, coyotes, fox, weasels, etc.
Your best bet to avoid becoming dinner is to spend a few short weeks
aboveground to frantically gather and store food, then return to your
relatively safe burrow for the next 8 months. If you are an elk and don’t even have
the luxury of hiding underground, you now have to deal with 6 feet of snow and
-40 degree nights.
Pronghorn seem to be the impressive exception to this stressful
reality, so if I had to be any animal in the park, it would be a pronghorn. For
starters, they almost always have more than enough food. Despite growing everywhere here, sagebrush is only eaten
regularly by one mammal: pronghorn. Sagebrush leaves are full of noxious
alkaloids that mildly poison most herbivores, but pronghorn have the right
complement of intestinal bacteria to break down and digest this otherwise
unpalatable forage. And if I were a pronghorn in a vast expanse of sage, I
would almost certainly be able to see a predator coming. My eyes would be so big
and set so far to the side, I could see more than 270° without even turning my head.
Now suppose a pronghorn was so focused on its sagebrush lunch that
a wolf managed to wind up within 50 yards of it. The wolf starts the chase,
running flat-out at 42 mph towards the surprisingly unconcerned antelope. At
this point, if I were a pronghorn, I would take a few more bites of sagebrush,
chew for a while, scratch an itch, stretch my legs, look at some clouds, and
maybe decide what direction I should move. No need to panic, because when I do
decide to distance myself from the wolf, I could do so at 60 mph, and I could
keep up this speed for a very long time. Within seconds I would leave the wolf
in hundreds of yards of dust, and merrily return to eating sagebrush.
Why evolve the ability to run so fast? It reminds me of the wily
coyote vs. the roadrunner. Natural selection in a predator/prey relationship
results almost every time in a prey species that is just barely faster than its predator. If you could run, say, 45 mph, you
could easily outrun the fastest thing chasing you in the western hemisphere.
Nothing requires a pronghorn to run
60 mph, so, ostensibly, there is no evolutionary advantage to do so. Well, not
anymore at least.
This is (a rendering of) a North American Cheetah:
Once the fastest thing in the world, it went extinct during the
last ice age.
The pronghorn has outlasted
its only historical predator, and now enjoys a life of bountiful food and
virtually no threat of predation.
The pronghorn in Grand Teton National Park have one more trick up
their sleeve. In the winter, the snow gets too deep for the antelope to move
around in. So they migrate. They head east over the Gros Ventre mountain range,
150 miles southeast into central Wyoming, where the snow is thinner and the
temperature ever-so-slightly warmer. It’s the second longest land migration in the
western hemisphere (after caribou in Canada). The “Path of the Pronghorn” is
known only by the 400 antelope that summer here in the park. They learned this
ancestral trail from their parents, generation after generation, and walk such
a reliable route every year that they leave, in some places, a trail as wide as
a road.
Isn’t nature awesome?