Our hardest to find resident bird is the boreal owl. These little balls of feathers are about 10 inches high and weigh less than five ounces. They reside in boreal forests and are most common in Canada. Until recently they were thought to only be winter visitors in Colorado, but there was evidence that they may be more than just seasonal in the state.
Coloardo State University’s Ron Ryder and his students set out to find hard evidence of breeding boreal owls in the early 1980s. Their study centered on Cameron Pass that straddles the boundary between Larimer and Jackson counties. The habitat was right – mature subalpine forests dominated by Engelmann spruce and subalpine fir – and boreal owls had been heard calling in the area. The work had to be conducted at night from March through May when owls are vocalizing. Sure enough, they found more than 25 calling males and eventually located several nests in old woodpecker cavities. The feeling is boreal owls have always nested here, but the fact that they favor high elevation forests and are generally only calling at night during late winter, made them difficult to find.
Upon hearing that the owls had been found just 20 miles to the north of Boulder County, some of us concluded “if they are there, they might be here.” Naturalist Steve Jones organized a research project in the mid 1980s through the Boulder County Nature Association to better document the numbers of all the small forest owls, including boreal, northern saw-whet, northern pygmy and flammulated. People went out at night via car, foot and skis to listen for the owls.
I worked the areas along the Peak-to-Peak Highway and west, including Brainard Lake, Caribou and the Fourth of July road. The full- moon period is a good time to go out and listen for owls, and it needs to be a fairly calm night, always a hard thing to find at high elevations.
Initially, I had good luck in finding calling northern saw-whet and northern pygmy owls. Then, one calm moon-lit night in April while on the Brainard Lake road, I heard the calling of a boreal owl on the hillside to the south. Their call is much like the winnowing of a common snipe, but hollower and less breathy.
Since then, boreal owls have been found breeding in the Southern Rocky Mountains from southern Wyoming to northern New Mexico. They have been heard and observed in Boulder County from Wild Basin to Hessie, and many places in between including Caribou and Chittenden. Most of my encounters with them have been at night, but a half dozen times I have heard them calling during the day, always when it is cloudy and sometimes outside of breeding season.
Boreal owl’s main food source is small mammals. They often prefer wet habitats near streams as these sites generally have good populations of small rodents that the owls can catch. Red-backed voles, most common in mature spruce-fir and lodgepole pine forests, are a preference.
If you manage to get out for a full-moon ski tour or walk in April, take the time to stand still and listen. You may hear a series of faint hollow whistles off in the distance from one of our more secretive fellow inhabitants. Of course, the key to good nighttime owling is no wind, which is not the norm for this neck of the woods, but if you get a calm night, open your ears.
April nature happenings in the Nederland area include the following.
Bird species returning from the south include common snipe, band-tailed pigeon, broad-tailed hummingbird (end of the month), red-naped and Williamson’s sapsuckers, tree swallow, ruby-crowned kinglet, yellow-rumped warbler (end of the month), common crackle, fox sparrow and song sparrow (sometimes they arrive in March and a few may even overwinter).
Late April is the peak time for great horned owls to hatch. Mammals tend to be emerging or moving. Snow level permitting, elk will begin a movement from their winter to transitional range. Chipmunks and ground squirrels may be seen during periods of mild weather. Black bears are emerging from dens in March and April. Their favorite foods at this time of year are vegetation and carrion.
The peak time for bobcat young to be born is April and May. Mink breed from late February until early April. Long-tailed weasel litters are born in April and May.
Butterflies that overwinter as adults, such as mourning cloaks, tortoiseshells and commas, may appear during periods of mild weather.
Pasque flowers may be found blooming on south-facing hillsides if the weather is mild enough.
March and April are prime time for hearing the calls of our small forest owls: northern pygmy-owl, northern saw-whet owl and boreal owl.