There are nearly 3,500 square miles of protected wilderness in Yellowstone National Park, but visitors can see only a small fraction of it from its 466 miles of road that wind through Wyoming, Montana and Idaho. The oldest national park, established in 1872, it is home not only to the famous geyser Old Faithful, but to over 300 different species of birds, fish and mammals — the largest concentration of mammals in the lower 48 states.

The visually stunning Nat Geo Wild special "Wild Yellowstone," which premieres Dec. 6, follows 31 different species found in the greater Yellowstone ecosystem (including Grand Teton National Park and the region's national forests), and we got a closer look at many of them on a trip to the park in October. Local expert and guide Taylor Phillips, who leads Eco Tour Adventures provided insights into this fascinating world.

1. The wolf population in Yellowstone numbers about 100 today, but it dropped to zero in the 1930s, when more than 50,000 were trapped, shot or poisoned under a program to eliminate predators. Wolves were reintroduced to the park in the mid-1990s, when animals were captured in Canada and released in the park. That had an effect on the coyote population in Yellowstone, as wolves search out coyote dens and kill the pups.

2. Bison are arguably the most dangerous animal in Yellowstone. They can run as fast as 30 miles per hour and their behavior is unpredictable. During the breeding season in August, males become more aggressive due to built-up testosterone, and they often take it out on nearby trees. But they’re not the only species that destroy trees. Bears strip them of bark, especially when sap is running, and beavers fell others: it takes nearly 100 trees to feed a family of beavers for the winter.

A grizzly bear and its cubsThe grizzly population in Yellowstone is lower than the population of black bears, but grizzlies seem more comfortable with people, which is why they're spotted more often. (Photo: Yellowstone National Park/flickr)

3. Black bears and grizzly bears exhibit some very different behaviors. Grizzlies don't climb trees very well; black bears do all the time. Grizzly bears have claws three to four inches long and do a lot of digging. They often dig their own dens, excavating 2000 pounds of dirt. Black bears don't have that ability and use existing cavities underneath rocks or trees. There are an estimated 500-600 black bears in the Yellowstone ecosystem and 675-850 grizzlies, but grizzlies are often spotted more often because, according to Phillips, they seem to be more comfortable with people and come closer to the road. Grizzlies, which live 25-30 years, are on the threatened species list. They’re slow to reproduce and have one to four cubs at a time that stay with their mother for two to three years.

4. There are between 11,000 and 12,000 elk — or wapiti, which means white rump — in the Yellowstone ecosystem, and many head south to the national elk refuge north of Jackson Hole in winter, where food is provided for them in the form of pellets. In mating season in the fall, males display their impressive antlers — the more points, the better — and sound a bugle (mating call) to attract females. One male bull can mate with as many as 30 females. They don't eat during this stressful time, and many succumb to starvation and predators in their weakened state. Those that survive drop their antlers every year and grow a new set. Females tend to congregate together but give birth in seclusion, usually to a single calf, though twins do occur. Many newborns fall prey to grizzly bears and wolves, but the survivors can expect to live from 12-15 years.

Bighorn sheep butt heads in Yellowstone National ParkBighorn sheep butt heads in Yellowstone National Park. (Photo: Nat Geo Wild)

5. About 80 percent of the country's pronghorn sheep are found in Wyoming. Most newborn fawns have been killed by coyotes in the past, but with a smaller population of the predator now, the pronghorn population has increased. The much larger bighorn sheep males literally butt heads, like in the picture above, with their rivals for dominance. Their horns alone weigh up to 30 pounds, a 10th of their body weight.

6. Lake trout are a non-native species of fish that were introduced to Yellowstone Lake in the 1980s by fisherman, and they're killing and replacing the native cutthroat trout, a prime source of food for grizzly bears. Since lake trout aren't as easy to catch as the cutthroats that spawn in river tributaries, grizzlies began to focus on elk for food.

7. Before it was banned in 1972, the insecticide DDT damaged the Yellowstone environment: it seeped into waterways and accumulated in the fish that birds ate, adversely affecting their birthrate. Populations were diminished, but have since bounced back to healthy levels.

Trumpeter swan flies over a snowy riverTrumpeter swans are the largest water fowl you can find in the U.S. (Photo: Kent Ellington/Shutterstock)

8. Trumpeter swans, the largest waterfowl in the United States at an average of 30 pounds with an 8-foot wingspan, have a small population in Yellowstone. Some migrating birds from Canada and Alaska spend the winter there, and the nests of a few year-round residents have been spotted.

9. Of the four species of moose in North America, the smallest is found in Yellowstone. There are fewer than 200 today, due to forest loss, predators and global warming. Moose are well adapted to cold and deep snow but don’t do well in temperatures higher than 60 degrees. With climate change causing more warm days, the stressed moose are producing fewer calves.

10. The iconic geyser Old Faithful is so named because it erupts roughly every 90 minutes, shooting about 7,000 gallons of water into the air. Park rangers measure the length of each eruption and can pinpoint the time of the next one. There are more geysers in Yellowstone than anywhere else on Earth. Steamboat is the largest, and its eruptions reach 300-400 feet. You can see one of the park's famous geyser's, Beehive, erupting in the video below:

11. In 1988, 12 different fires destroyed 900,000 acres of forest in Yellowstone. Because of the dry climate, many of those charred trees are still standing.

11 facts you never knew about Yellowstone
The fascinating secrets of America's oldest national park.