Dave Hallock, Peak to Peak.

Evening can be a magical time for learning about our fellow inhabitants. Some types of wildlife are most active at night, with special equipment (eyes and ears) designed for hunting in the dark. For those animals that can carry out some of their life functions (feeding, courtship, raising young) at night, they find a landscape where humans are home and inside. In essence, the available habitat for nocturnal animals increases at night.

One group of birds most active at night is owls. Their ears and eyes allow them to zero in on prey at night, most often small mammals, while their flight is quieter than a mouse. Owls have uniquely developed hearing systems that allow them to locate even faint sounds with remarkable accuracy. Their silence on the wing comes from a serrated (rather than smooth, as most birds) forward edge of the first primary feather. This disrupts the flow of air over the wing while in flight and eliminates noise, allowing the owl to arrive upon its prey without a sound.

Probably our most seen and heard owl is the great horned owl. They are also our largest owls, having an average body length of 22 inches. Their call is a series of 4 - 7 loud, deep hoots, the second and third hoots often short and rapid (the staccato second and third hoots are more common of females). Their calling and courtship begins in earnest in January and February. Egg-laying peaks in mid March and hatching in late April, with nests generally being made of sticks and shredded bark (often abandoned nests of hawks or squirrels) and located high in trees. Their favorite foods include rabbits and rodents. Diane Brown and I vividly remember one winter morning when we started out on a ski trip over at West Magnolia. We saw a large silent bird flying toward us down the trail with its talons full of prey. Just before it reached us, the great horned owl dropped what it was carrying; a snowshoe hare in winter coat.

We also have several small owls that inhabit our region. The two most common are the northern pygmy-owl and the northern saw-whet owl. A third, the boreal owl, is found in higher elevation forests. Pygmy owls average 7 inches in body height; saw-whet owls average 8 inches and boreal owls 10 inches. All three owls nest in abandoned tree cavities. Calling activities peak in March through May, with the full moon period in April being the best for hearing these birds. The main call of the saw-whet owl is a repeated single-note (sometimes paired) hollow whistle at a rate of 2-3 per second. Pygmy owl calls are similar, but slower (1-2 whistles per second) and more monotonous.

Boreal owls sound similar to winnowing snipes; a rapid series of ascending notes, but hollower and less breathy than the wetland loving snipe.

Not much was known about the numbers of these small owls in Boulder County until naturalist Steve Jones organized a research project in the mid-1980s through the Boulder County Nature Association. People went out at night via car, foot and skis to listen for the calling owls. Pygmy and saw-whet owls were found to be fairly common in the foothill and montane habitats of the county, with saw-whets also venturing into subalpine areas.

Prior to the BCNA study, boreal owls had not been recorded in Boulder County, but a study in the early 1980s by CSU biology students located 27 boreal owls near Cameron Pass in western Larimer County, just to our north; we speculated if the owls were there, they were likely here. Sure enough, we documented the first calling boreal owl in the county while skiing at night along the Sourdough Trail near Brainard Lakes. Since then, they have also been found at several other locations, including Hessie. Boreal owls generally inhabit mature to old-growth forests. Their main food is the red-backed vole, whose populations also peak in older high-elevation forests. They are one of the primary owls of the boreal forests of Canada but extend their range south through the Rockies into northern New Mexico.

Two other types of owls may be present in our neck of the woods. Long-eared owls are infrequently found in the mountains. They have been documented nesting at 10,700 feet in Rocky Mountain National Park. They are slightly smaller (15 inches in length), slenderer, and lack the white throat of the larger great horned. There is a feeling that long-eared owls are being displaced by the more aggressive great horned owls who live more comfortably around people. The flammulated owl is another small owl, averaging 7 inches in height, and is most common in lower elevation ponderosa pine forests.

While owls are most active at night, sometimes they can be spotted during daylight. A good clue that an owl may be present is if you hear a group of other birds making a lot of scolding noises in the forest. Chances are they are mobbing an owl. We are not sure why other birds, like chickadees and jays, mob owls that may eat them. Some speculate that it is akin to trying to catch 1 ball when10 are thrown at you at the same time. So maybe they are confusing the owl. At any rate, if you hear birds making a lot of commotion, take the time to look in the nearby trees. Keep looking for it. It may take a long time to see a 7-inch bundle of feathers tucked on a limb near the bole of the tree.

So, if you manage to get out for a full moon ski tour or walk in April or May, 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 our neck of the woods. But if you get a calm night, open your ears.

Following are some of the April nature happenings in the Nederland area. Bird species returning from the south include Wilson’s snipe, the band-tailed pigeon, broad-tailed hummingbird (end of the month), red-naped and Williamson’s sapsuckers, tree swallows, ruby-crowned kinglet, yellow-rumped warbler (end of the month), common crackle, fox sparrow, and song sparrow. Late April is the peak time for great horned owls to hatch. April is a prime time for hearing the calls of our small forest owls: northern pygmy-owl, northern saw-whet owl and boreal owl.

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.