[This is part two of a series of posts featuring photos from our March programs in Yellowstone with Natural Habitat Adventures and Wildlife Expeditions of Teton Science Schools.]

A big bull interrupting our preparations for a snowshoe hike

This week in Yellowstone featured the bison. Granted, it’s almost impossible to visit this park without getting stuck in the middle of a bison herd at some point. But the contexts in which we saw these big ice-age behemoths this week really showcased the lives they lead and the hardships they endure.

Bison walk on packed paths to avoid breaking trail in deep snow. This guy picked our path to walk on.

The thick, dark fur on their face protects their skin from the abrasive icy crust they must break to access grass beneath.

Bison are built for life in winter. Their massive head and shoulders effortlessly dig through snow to the forage below. Their gut is adapted to pull every last bit of meager nutrition from the dead grass they depend on. Their fur is so well insulated, snow and frost builds up on their backs by the inch. They seem to have a radar for finding the highest-quality food available under any snow depth. They consistently find the easiest travel routes and the safest valleys.

Even with these physical and behavioral adaptations, though, life is still tough. Winter is a time of perpetual starvation, insanely cold temperatures, and serious vulnerability. As winter draws on, ribs and hips become more and more defined. Grass becomes scarce. Wolves become stronger and braver.

Under this pressure, many bison find the roadway and follow it west. They follow it past the Lamar Valley, where their kin were restored to today’s healthy numbers after teetering at the brink of extinction. They follow it past Crystal Creek, the reintroduction site of the one wolf pack that specializes on hunting bison. They follow it past Blacktail Lakes, where a few bulls fall through thin ice and drown every year.

This calf has nearly survived his first Yellowstone winter.

Bill bison walking through the Lamar Valley, the historic Buffalo Ranch in the background.

By the end of the winter, some bison look like skin draped over bones. Green-up can't come soon enough.

Even in winter, there is fresh forage available along the shore of some spring-fed creeks.

They arrive at the Gardiner Canyon, and follow the river downhill to the edge of the park. At this low elevation, the ground is snow-free and the temperatures are spring-like. Having found what seems like an oasis at the end of the bitter winter, the bison walk through the Roosevelt Archway, crossing an invisible but significant border between Yellowstone National Park and Gardiner, Montana. Here, bison are no longer property of the American People. They are not ogled and admired by tourists and naturalists. Instead, they are legally considered escaped livestock. The farther the bison venture beyond the arch, the tighter the rubber band of state tolerance stretches. Eventually, that ecological oasis is replaced by a political minefield.

Behind the gate, bison are managed "For the Benefit and Enjoyment of the People." Beyond it, they are considered escaped livestock.

Some bison, you see, carry a disease called brucellosis. This disease causes failed pregnancies and therefore kills the reproductive potential of the herd. The problem is, this disease affects cattle too. Montana is considered a brucellosis-free state with respect to livestock, so stock growers can transport cattle across their state line without penalty, fee, or testing. Should Yellowstone bison intermingle with cattle and transmit brucellosis into domestic herds, the whole state’s brucellosis-free seal would be revoked, with devastating effects to the livestock industry.

So when a few hundred bison venture out of the park into the Gardiner Basin at the wrong time each year, their fate is gloomy. This year, about 600 bison were removed after leaving Yellowstone. In years past, these migrants were killed by the thousands. That still happens, but not with such reckless abandon as in previous years. Instead of an outright firing-line at the border, the herd is now rounded up and brought to slaughter, the meat given to Native American tribes. About 200 bison met this fate this year.

One of the park's biggest bulls looking for fresh grass along the Yellowstone River.

Upset by the annual annihilation of America’s most treasured bison herd, advocates and managers are now trying to design solutions that please all stakeholders. For instance, researchers have just concluded that with proper quarantine, testing, and culling, you can definitively declare a group of bison “brucellosis-free.” With this stamp of approval, the bison can be brought to Native American reservations to be used as agricultural and cultural resources. Or be brought to Ted Turner’s huge conservation ranches. In the future, the cleared bison may be the source for restoration herds on the American Prairie Reserve or the Tribal National Park.

A small herd of females and calves passing by.

Only 60 bison were quarantined this year. About 200 were consigned to slaughter. What happens to the remainder? Native American tribes are given special permits to exercise century-old treaty rights to hunt bison off-reservation under their own rules and regulations. These hunts accounted for roughly 263 bison this year. It’s nice to see the federal government following through on some much-needed reparations, especially after we slaughtered 99.999% of America’s bison to starve out the Indians. However, these tribal hunts have meant that gut-piles and bloody snow litter the Gardiner Basin, making for some interesting discussion on wildlife watching excursions like ours. Native Americans are also in disagreement over the ethics of hunting these animals in such circumstances.

Things are looking promising for these big guys. Which is good, because they have enough to worry about as it is. The Montana Supreme Court just ruled that bison may now be legally tolerated in roughly 400,000 acres outside the north and west entrances. Also, the World Wildlife Fund and the Intertribal Buffalo Council are working together to establish tribal quarantine facilities so that more wandering bison can be held and transferred to reservations and restoration projects instead of being killed.

A train of bison walking through the Gardiner Canyon, heading towards the park's boundary.

Hopefully, with continued conservation efforts, fewer of these Yellowstone migrants will be economic nuisances to the cattle industry, and more will become the pioneers of new herds across the Great Plains.

An hour-old bison calf standing for the very first time. May 2013.