Migrators are a sign of the season in High Country
When we turned the calendar from August to September, Mother Nature took the opportunity to remind us fall’s on the way, with cold weather marking the transition for us – and reminding the animals it’s time to start thinking about moving on to warmer climates.The cooler evenings and longer nights not only require us to shrug on a jacket, they’re also signs for wild animals. They’re cues for their winter survival.Summit County has year-round residents like the magpie, snowshoe hare and red fox, but other animals migrate. And it’s not just southward from our neck of the woods. Sometimes it’s just to lower elevations. Other times, it’s further underground.Starting as early as July, birds, mammals, fish, reptiles and even insects are on the move.The above-ground traffic increases this time of year with wildlife from other areas of the country and beyond. Colorado is part of a major North American flyway, or “bird superhighway” for migration, meaning the valleys, rivers and lakes serve as a rest stop as animals from elsewhere move south. Some species only migrate through our state, and spring and fall is our only chance to catch a glimpse of these travelers, like the cinnamon teal or arctic peregrine falcon.Some are very visible, like the flocks of geese that cruise in a “V” formation across the sky above the Tenmile Range. Monarch butterflies may make their way through. And the movement of sandhill cranes across the plains is a popular bird-watching option.Shannon Schwab, district wildlife manager with the Colorado Division of Wildlife, said sandhill cranes also pass above Summit County, but they fly high.”If you know what to listen for, you can hear them,” she said.
Some leave together in large groups, like Swainson’s hawks or white-throated swifts. Others that commonly migrate in the daylight include pronghorn, loons, white pelicans, swallows, nighthawks, hawks and vultures (larger raptors need to take advantage of thermal updrafts from the heat of the sun).But still others are more discreet. Corridors on the side of the highway allow deer, elk, sheep and goats to go to lower elevations to browse and look for mineral licks, but they tend to travel near dawn and dusk – followed by mountain lions. Bats, owls, ducks and other waterfowl, tanager, buntings and other songbirds often travel at night and rest and refuel during the day. This way, they can find food easier, or take advantage of darkness as cover from predators.And underwater is another story. We might not see it, but Colorado’s pike minnows migrate long distances from their spawning sites to calmer pools and eddies for the winter.Meanwhile, Kokanee salmon head upstream to attempt a spawn – sometimes as far as the inlet of Green Mountain Reservoir clear to Silverthorne, and along the Upper Blue River from the Dillon Reservoir inlet toward Breckenridge.Brown trout are also making the move, which generally takes about a month to two months to complete. They hang in water pockets and eddy jump upstream to lay their eggs. Both types of fish die after the spawn, Schwab said.
Often, it’s the shorter days that triggers hormonal changes in the pituitary gland that initiate a physiological response. Animals get “twitchy” or restless and spend less time sleeping and more time on the move.Surviving the cold, much of it having to do with food sources, is another reason to move on. They depart to routes that have served them and their ancestors for generations.”Their instincts are to move to areas where foraging will be easier for them in the winter,” Schwab said. “So they’re going to move to areas where it’s easier to live. Whether it be food, shelter, weather.”Deer and elk are Summit County’s biggest source of movement, Schwab said, the next being the birds. Big game begin moving in fall, when pressures increase from weather and snow, as well as hunters.Much of their wintering ground is downvalley, east of Green Mountain Reservoir, “where there’s open sagebrush to feed on and less snow,” Schwab said, adding that other big game head south to Park County. Still others stick around for winter if they’ve found good forage to last through winter.”What changes year to year is the amount of snow that pushes (big game) to those wintering grounds,” Schwab said. “If we get a lot of snow early on, they’ll make a bigger push to get those wintering grounds earlier than they would have the year before.”Movement can also depend on breeding cycles, as babies born in spring become independent enough to make the trip, or, like elk, fall begins the annual mating season.As they enter the rut, as it’s known, elk behavior is all about a male trying to get as many females in his harem as possible and breed with them. The displays of dominance and the unique bugling call are characteristics of the fall mating season. Because of hunting and recreation pressure, it’s not common to see or hear elk in Summit County; Estes Park and Rocky Mountain National Park are likely the closest spots to see the rut in action in the open.”You certainly can hear them, but getting to see them is probably more likely by hunters,” Schwab said, adding that the best chance to see them is in the evenings.
Some animals, our year-round residents, are able to forage under mounds of snow. Rodents, squirrels and snowshoe hares are examples of animals capable of foraging in what’s known as the subnivean parts of the forest – what grows between the snow and the Earth. Fox, lynx and coyote stick around because their small mammal food source remains. Some elk stick around through winter in Keystone and along the Tenmile Range. Deer remain in and around housing subdivisions. Goats and bighorn sheep also remain regular residents, as do many moose and bears, who can move large distances but generally prefer to stay and den in Summit County, Schwab said.
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