It’s 20 degrees outside but suddenly the frozen world vibrates with music.
Most birds are as silent as the snow, but three songsters are undaunted by the cold. Townsend’s solitaires, American dippers, and red crossbills sing joyously throughout the winter.
Sometimes called “Johnny-one-note” because of their usual monotonous call, both male and female Townsend’s solitaires sing a gorgeous, complicated tune often delivered from the top of a juniper tree.
Because these members of the thrush family require between 42,000 and 84,000 juniper berries to survive the winter, they sometimes engage in fierce battles over berry bailiwicks. A good place to look and listen for them is along the Skunk Creek Trail.
American dippers, our only truly aquatic songbirds, excel both in foraging for insect larvae under cataracts and in singing while perched on the edge of the ice. Their bubbling cadenzas seems to mimic the turbulent cascades they favor.
Although they don’t migrate south in winter, many water ouzels (an older, more poetic name for this bird) make short altitudinal migrations from the high country to unfrozen creeks and rivers. Boulder Creek is a good place to find them.
Red crossbills nest any time of year, including the depths of winter, whenever and wherever there are sufficient cone crops to feed the young.
When establishing and defending nesting territories, they sing a soft, finch-like song that ornithologist David Sibley transcribes as: “tikuit ti chupity chupity tokit kyip kyip……”
They have been particularly vocal recently along the Shanahan Ridge Trail.
Great horned owls hoot rhythmically and often duet soulfully for hours in winter — their mating and nesting season. Secretive marsh wrens, with a repertoire of more than a hundred song phrases, can sometimes be heard from the boardwalk at Walden Ponds.
Other species, such as song sparrows and robins, occasionally engage in song, and most birds utterchips, chirps, and other vocalizations to keep the flock together and to share information about food or predators. Few birds, however, burst into full song for good reasons.
Singing uses up calories and can attract predators. The cost might be worthwhile during mating season since a singing male attracts more females, but why take that risk when mating is over? The usual answer is that the birds are defending winter territories.
Another possibility is that they are practicing for courtship or laying claim to next spring’s nesting territory. Or, could singing be a byproduct of increasing testosterone prior to mating? Or, might they sing for the sheer joy of singing?
When we hear a tiny dipper emerge from icy water to let loose with a cascade of song, we can almost hear Pete Seeger belting out “How can I keep from singing”!
A recent study by Marjorie Sorensen on reed warblers wintering in Africa argues in favor of the rehearsal theory. After performing experiments to rule out other theories, Sorensen recorded the warblers and found the songs were more “meandering” with a slower tempo than summer songs.
She hypothesizes the birds are working on new material that’s not yet “crowd-ready, instead of trotting out old standards.” She also found that the most enthusiastic winter vocalists were drab males that needed song instead of colorful plumage to lure a mate.
Perhaps there are multiple and mixed reasons for different species to sing in spite of snow, sleet, and storm. Finding the reason for winter singing seems to open up an endless supply of dissertation topics.
To hear snippets of song from these jubilant choristers, Google Cornell’s “All About Birds” website and click on “sounds.” Another database that includes only Colorado recordings is tinyurl.com/Xeno-Canto-Colorado.
Ruth Carol Cushman and Stephen Jones are authors of “Wild Boulder County” and “The North American Prairie.”