In an ecosystem with the dramatic seasonal temperature swings of Grand Teton and Yellowstone National Parks, the landscape and wildlife can look remarkably different from month to month. If you have only visited the parks in one season, returning to visit in another time of year will reveal a whole new world of wildlife activity. Here is a calendar featuring some of the wildlife highlights from month to month across the Greater Yellowstone Ecosystem.
March
Most of the Greater Yellowstone Ecosystem is still covered in snow in March, but the first signs of spring are arriving. Lower elevations are melting out, eagles have already mated and are on their eggs, and the first Mountain Bluebirds have arrived to feed on early insects on the snow. The contrast of a bright blue bird against the bright white snow highlights the plumage of the male mountain bluebird at its most stunning – perhaps for a good reason, as the first females also arrive and are beginning to choose their mates.
April
While the first grizzlies of the season may emerge from their dens as early as late February, April is the peak of bear sightings in Grand Teton and Yellowstone National Parks. Both black bears and grizzlies have emerged and are readily seen in open areas, feeding on fresh spring grasses, roots of meadow plants, and old carcasses from winter-killed animals. Wildlife watchers eagerly await the appearance of female bears with cubs, some of whom use the presence of humans to avoid the attention of more road-wary male bears and other predators.
May
For birders, May is the peak of bird diversity and sightings in the park. Most of our resident breeding birds have arrived and are busy competing for territory and mates. Males are in their brightest colors and most vocal behavior. May is also the time to look for migratory populations of water birds such as loons and ibises as they stop by for some good meals on their journey north. But what for many is the birding highlight of the year is the brief visit of the Harlequin Duck. Harlequin ducks from their Pacific Ocean winter homes to feed and court in the whitewater of area rivers before parting ways for the rest of the year.
June
Spring produces the most lush, digestible plant growth in the parks, and the hooved animals give birth in spring to take advantage of it. Almost all hooved animals, or ungulates, reach the peak of birthing activity in June – the exception is the bison, which typically reach the peak of calving in May. Many ungulate young are orange to blend in with the green grass. Wait a moment – orange, blending in with green? That doesn’t make much sense! But when your main predators are large carnivorous mammals – coyotes, wolves, cougars, and bears – an orange color is perfect camouflage against green because most mammals are red-green color blind.
July
When the bison calves begin to swap the red-orange color of newborns for the standard dark brown coat they will sport the rest of their lives, the male bison have already begun to think about starting the next year’s crop of calves. The bellows, threat displays, rolls in dusty urine-soaked wallows, and rare serious fights begin to shake the landscape with their power. A male will attempt to isolate a female approaching estrus for several days and must stay alert, as the window for breeding only lasts a few hours. Breeding behavior begins in June and continues through September, but reaches its peak in July and August.
August
As the green grasses of summer fade into the golden grasses of autumn, the rodent population is at its peak. Hundreds of migrating birds of prey, especially juveniles, arrive in the local grasslands and sagebrush flats to take advantage of the abundant food source. Kestrels, Prairie Falcons, Northern Harriers, Swainson’s Hawks, Redtail Hawks, and Ferruginous Hawks are the most likely species to encounter and can be seen in the ecosystem through autumn before they leave to avoid the deep snows of winter.
September
If you would like to see a pronghorn reach a speed of over 50 miles per hour, September is the best time of year to observe these elite athletes show off their skills. Males accompany small groups of females and are kept busy not only chasing off rival males, but also trying to keep the females together. When they return to their harem after escorting a rival miles away, we can often observe the black tongue as they pant – a trait they share with their closest living relative, the giraffe.
October
By early October, the golden leaves of aspen are at their peak and so is the rut of the Rocky Mountain Elk, or Wapiti. The mountains echo with the bugles of the males, a behavior that intimidates other males and impressed the females. A successful male could lose up to 25% of his body weight as he is run ragged breeding with his harem of females and chasing rivals. Satellite bulls – younger or less impressive bulls – stalk the edges of the harem, always alert for a moment of distraction from the large bull. The first bugles of the rut can be heard as early as late August, but the peak of the breeding season runs from mid-September though mid-October.
November
November is the month of transition from fall to winter and is the best time of year to observe and photograph bull moose. While their breeding season parallels the elk in September and October, they are actually more readily visible in November and December as temperatures cool down and cloudy weather increases. Dozens of moose emerge in Grand Teton National Park to feed in areas with high concentrations of Antelope Bitterbrush, a high-protein shrub that the deep snows of winter and the high temperatures of summer prevent them from accessing at other times of the year. Bull moose retain their antlers through November in hopes of perhaps attracting a female that is late into estrus, but as winter hits hard in December, the antlers are a mere burden and begin to shed. By February, it is unusual to see a bull moose with antlers until they begin the process regrow in May.
December
After the rest of the hooved animals have had their moment of glory, it is time for the bighorn sheep to shine in December. By this time of year, the deep mountain snows have pushed the mountain sheep down into the valleys where they are more readily visible by visitors. December is the best time of year to observe and photograph the battles between the rams over the ewes, and the dramatic chases that ensue when an ewe becomes receptive to breeding. Whether it is by nature or the fact that their low population results in little hunting pressure, bighorn sheep are remarkably tolerant of human visitors and photographers.
January
In the silent, frosty month of January, the rivers of Yellowstone come alive with the trumpet of the swan. The hot springs of Yellowstone and the surrounding region feed into the creeks and rivers, preventing them from freezing over and promoting the growth of rich plant life for swans to feed on. It becomes the winter vacation destination for thousands of Trumpeter Swans migrating south from Alaska and Northwestern Canada. One of the January highlights is watching a pair of pure white swans cross a gray winter sky, their resonant calls echoing off the surrounding mountains.
February
As winter progresses, February becomes the month of the wolf. Weakened by lack of food and deep winter snows, their hooved prey becomes easier to catch. The oversized paw of a wolf helps them float over the snow that bogs down elk and deer. Extra fur grown each winter between the toes help spread the foot even wider, acting like snowshoes. February is also the peak of the breeding season for wolves, so individuals are more likely to be seen as they split off from their natal pack and seek a mate. Howling, which chiefly serves as a communication tool amongst wolves, also peaks in February as packs settle their borders.
