Even for the biggest land animal in North America, life can start out on the perilous side of things. A ranger at Yellowstone National Park recently documented this truth in a series of photographs that's attracted quite a bit of media attention.

The images, captured in the vicinity of Madison Junction in the western part of the park, show some life-or-death drama going down between a straight-out-of-the-womb bison calf and a determined coyote. There's a critical third player in the cast of characters, too: the mother bison.

Image: Ranger Joy Guffy via YellowstoneNPS/Facebook

"The cow was worn out from giving birth and the calf was unable to stand yet," Ranger Joy Guffy, the photographer, reported on Yellowstone's official Facebook page.

Despite her weariness, the bison cow wheeled and parried with the darting coyote, which in one picture has managed to get its teeth on the chestnut-brown newborn.

"The coyote was ultimately unsuccessful," Guffy wrote, "but all three appeared to be exhausted from the interaction."

Image: Ranger Joy Guffy via YellowstoneNPS/Facebook
Image: Ranger Joy Guffy via YellowstoneNPS/Facebook
Image: Ranger Joy Guffy via YellowstoneNPS/Facebook

Bison calves are "precocial": that is, they're up and about shortly after birth, able to travel with their mothers and the rest of the herd basically off the bat. This "follower" strategy – which contrasts with hoofed mammals such as elk, whose young initially hide under cover – makes sense for bison and many other open-country ungulates, given how exposed their offspring are. (Some smaller grassland grazers, however – including the pronghorn that shares the American steppes with bison – are "hiders" as newborns.)

In American Bison: A Natural History, zoologist Dale Lott noted that infant bison usually take no longer than seven or eight minutes to stand up. In that narrow window of relative helpnessness, a freshly delivered baby buffalo certainly makes a tempting target for a coyote – but as the recent Yellowstone incident demonstrates, the presence of a horned, half-ton mother is usually enough to thwart a predator.

Bison cows often isolate themselves to give birth, but once the calf is mobile, the pair rejoins the herd: a newborn moving about within the group is already that much less vulnerable.

In Wood Buffalo National Park on the boreal border of Alberta and Northwest Territories, wolves – a much more formidable potential bison predator than a coyote – selectively target bison herds with calves in early summer, but youngsters often escape by fleeing within or in front of the herd (or courtesy of some active, belligerent defence from both cows and bulls).

By a few months old, a bison calf is big and strong enough on its own to present a pretty formidable challenge for a coyote, at least one acting alone.

A coyote's best chances come when a young bison calf somehow finds itself separated from mother and herd alike. In 2009, that opportunity arose in northeastern Yellowstone: when a group of bison cows and calves swam across the Lamar River, one youngster was swept downstream and left behind. Abandoned on shore, the calf had the misfortune of being discovered by the alpha male of a resident coyote pack. It still took the wild dog some 3.5 hours to actually kill the calf, which landed a few hoof blows before finally succumbing to a drawn-out throat bite.

Humans witnessed another intriguing case of attempted coyote predation on bison in Yellowstone a few years after the park reintroduced gray wolves. In March 1999, observers saw a single wolf attacking a malnourished buffalo calf from the front, with two coyotes worrying it from behind. This was no coordinated interspecies effort on the part of the canids: after killing the calf, the wolf drove off the coyotes (though they hung around for scraps).

On the rough-and-tumble wilderness stage of Yellowstone, bison calves aren't just under threat from coyotes and wolves. In 2000, observers watched a sow grizzly run down a bison calf travelling with its mother in the park's Hayden Valley, one of the core geographies for Yellowstone's central bison herd. Though the cow did charge at the bear once it had caught the calf, the grizzly held her ground (in very non-coyote fashion), and after some 15 minutes the cow abandoned the scene. 

As the authors of a paper on the incident note, the cow and calf likely made a tempting target because they were alone. "Situations where cows with calves are isolated from herds or mixed groups as in the incident we described are uncommon except for a short period during and immediately after calving," they wrote. Bison groups have been seen presenting a tight-packed flank around calves at the approach of a grizzly, successfully convincing the bear to pursue easier dining options elsewhere.

A bison that survives its calfhood will grow into a huge humped beast that, on the whole, can move around pretty confidently among the rich predator cadre of Yellowstone National Park. And if it does, the buffalo – like so many of us –will surely have a mother to thank.



Top header image: Yellowstone National Park/Flickr