Other common small mammals include the wily, weasellike marten, found in coniferous forests; the playful river otter, found in rivers, lakes, and ponds; and two species of weasel (also known as ermine), widespread in both willows and spruce–fir forests. Beavers dam watercourses and cobble together lodges adjacent to trails in both parks.
Animals rarely seen by hikers include the sagebrush-loving badger and the red fox, found in the Lamar Valley and around Canyon Village at the edges of forest and sagelands. A recent three-year study confirmed the presence and reproduction of the wide-ranging Canadian lynx, which hides out in remote subalpine forests, on Yellowstone’s eastern flank. Other rare mammals include the relatively scarce raccoon; the carnivorous, forest-dwelling fisher; the weasel-like mink, occasionally seen in riparian forests; the striped skunk, seen flitting between the forest and riparian zones; and the fierce, elusive wolverine, the largest land member of the weasel family. Researchers live-trapped and released a wolverine in March 2006 just north of Yellowstone park—pretty impressive given the animal’s 350-to 500-mile range.
Three territorial species of chipmunk are common in conifer forests. Four squirrel species are common around rocky outcroppings in forests. The yellow-bellied marmot is commonly seen, or at least its high-pitched whistle is heard, where trails traverse rocky slopes. The bleating, round-eared pika is also common in this kind of landscape. Other rodents often spotted scurrying about the forest understory include gophers, mice, several species of voles, shrews, muskrats, bushy-tailed wood rats, and porcupines.
At last count, 322 bird species were winging around the skies above Greater Yellowstone, with 148 of those observed nesting. Early morning in spring (from mid-May through early July) is the best time for birding. While hiking around lakes and waterways, keep your eyes peeled for big raptors such as the threatened but recovering bald eagle and trout-loving osprey swooping around hunting for prey. Majestic but imperiled trumpeter swans range between Montana’s Paradise Valley and the Madison River. The reintroduced peregrine falcon, which preys on songbirds and waterfowl, nests in Yellowstone and is well on its way to recovery but is rarely seen.
Other common species that exhibit entertaining antics include the boisterous Clark’s nutcracker, the diminutive mountain chickadee, the mountain bluebird, and Steller’s jay, a bold scavenger. Other monitored species of special concern include the American white pelican, common loon, harlequin duck, osprey, colonial nesting bird, and great gray owl.
Yellowstone contains one of the most significant aquatic ecosystems in the United States. It’s home to 16 fish species: 11 native and 5 nonnative. Since 2001, regulations have required the release of all native sport fishes hooked in park waters. The fishing season runs from Memorial Day weekend through the first Sunday of November.
The three subspecies of native cutthroat trout are an essential but increasingly threatened source of grizzly sustenance. They are being eaten out of house and home by the proliferation of illegally introduced, nonnative lake trout, also known as mackinaws. Other native sport fish are the rare, protected Arctic grayling and the slender, silver mountain whitefish. Introduced sport fish include brook trout, brown trout, rainbow trout, and lake chub.
Bald eagle nest: Eagles are often found fishing for trout around Heart Lake (Trail 22).
Six species of reptiles (prairie rattlesnake, bull snake, valley garter snake, wandering garter snake, rubber boa, and sagebrush lizard) and four decreasingly common species of amphibians (boreal toad, chorus frog, spotted frog, and tiger salamander) are found in Yellowstone. Encountering a poisonous prairie rattlesnake in Yellowstone’s low-lying Northern Range is unlikely but possible.
More than 12,000 insects, including 128 species of butterflies, provide fodder for many quick-tongued predators. Of greatest concern to hikers are mosquitoes (see Trail Safety).
When to Go
As two of North America’s most popular summer destinations, both parks have the unfortunate reputation of being overcrowded, especially Yellowstone. This certainly can be true on major holiday weekends, on heavily trafficked roads, and at campgrounds and must-see attractions, but solitude is not hard to come by—if you know where to look.
Both parks are four-season recreation destinations. Less than 5% of Yellowstone’s visitors arrive between November and April. Likewise, in Grand Teton 80% of visitors arrive between June and September. Annual Yellowstone visitor numbers have risen noticeably in the past 15 years to almost 4 million (most coming via the West Entrance), while Grand Teton averages around 3 million.
Thankfully, even in summer, escaping the crowds is reasonably easy, especially in Yellowstone. To find solitude, head for the backcountry. Surveys by the Park Service found that less than 1.5% of visitors apply for a backcountry permit in Yellowstone; only half of 1% do so in Grand Teton.
To avoid crowds, especially in the frontcountry, the usual rules of thumb apply: visit midweek instead of on weekends, and during spring and fall shoulder periods. Some of the finest hiking conditions coincide with diminishing crowds after Labor Day weekend and the peak of fall-foliage colors. The last week of August is a good time to come, for its combination of summer weather and slightly lighter crowds.
Accommodation in Yellowstone is a different matter. During the peak months of July and August you need to have booked your park accommodation at least six months in advance (some rooms sell out a year in advance). Even the reservable Xanterra campsites are often booked up a month in advance in summer. Unreservable park campgrounds are generally full by noon, with many campgrounds full by 9 a.m. Reservations are essential in Yellowstone. There’s more room to move in Grand Teton, since most of the campgrounds are nonreservable, but you’d be wise to book RV sites in advance and make your lodge reservations at least six months ahead.
Weather and Seasons
Throughout Greater Yellowstone, conversations (and tall tales told by the fireplace over a posthike pint) are peppered with anecdotes about the region’s famously mercurial weather. Snowfall has been recorded every single day of the year here, so the best advice is to always come prepared for the possibility of extreme conditions and four seasons in a single day. Locals claim there are nine months of winter and three months of relatives. This isn’t that far from the truth. Perhaps the most reliable climate-related axiom is, “If you don’t like the weather, just wait five minutes.” In any case, on any given day, Yellowstone is often the coldest spot on a US weather map.
Always be ready for afternoon thundershowers (locally called “rollers”) and to beat a hasty retreat from the higher elevations when lightning threatens. Because conditions on the trails change as quickly as the weather, it’s best to check in with a ranger station before hitting the trail, even if you’re only going for a day hike.
Given the right disposition, conditions, and over-snow travel gear, winter can be the ideal season to explore the parks in relative tranquility. During winter, the mercury hovers around 0°F during the short daylight hours, with occasional highs in the 20s. Subzero overnight lows are the norm. Infrequent warm “chinook” winds push daytime highs into the 40s. Annual snowfall averages 150 inches in most of Yellowstone, with 200 to 400 inches routinely recorded at higher elevations.
Yellowstone’s winter tourism plan has been in flux for the last decade, as the park tries to balance the demands of local communities while limiting the number of snowmobiles through the park each day. As of winter 2016–2017, Yellowstone National Park allows a maximum of 110 daily “transportation events” (defined as one snow coach or group of snowmobiles) to enter the park. Only half of these “events” can be snowmobiles. The plan also allows one noncommercially guided group of up to five snowmobiles to enter through each park entrance every day. Noncommercial guides