Colorado is famous for mountain peaks, high country wildflowers, and iconic alpine wildlife, like bighorn sheep, mountain goats, pika, and ptarmigan. But one of Colorado’s more secretive alpine wildlife species remains a mystery.
A migratory songbird known as the Brewer’s Sparrow is a small, nondescript, brownish-gray bird, the ultimate “little brown job” or “LBJ” as they are known to birders. This species is known more for its long, buzzy songs than its looks, but long-term declines in populations and threats to their habitat make Brewer’s Sparrows a priority for research, management, and conservation.
The subspecies that breeds in Colorado, the sagebrush Brewer’s Sparrow (Spizella breweri breweri), is typically considered a “sagebrush obligate” because it nests almost exclusively in sagebrush. Since the early 1900s, reports have occasionally surfaced of Brewer’s Sparrows in willow and krummholz in Colorado’s high country, including some well-known locations like Mount Evans, Guanella Pass, and the Flattops Wilderness. But the identity of these birds remains unknown. A less well-known subspecies, the “Timberline” Brewer’s Sparrow (S. b. taverneri), nests in stunted shrubs and krummholz near treeline in the Canadian Rockies, but their closest known breeding populations are in northwestern Montana.
Undiscovered Populations of the Timberline Sparrow?
Are Brewer’s Sparrows in alpine areas of Colorado previously undiscovered populations of the Timberline Sparrow? If so, it would extend the subspecies’ known breeding range more than 800 miles south. Or are they simply sagebrush Brewer’s Sparrows using non-typical habitats? Or are they sagebrush birds that nest in low-elevation sagebrush in spring, then move upslope in summer to nest again in alpine willows, a phenomenon known as itinerant breeding? Or, an outside possibility, are they a third subspecies altogether?
As an avian researcher with Colorado Parks and Wildlife, I set out to answer this question this past May. I first compiled historical and recent records of Brewer’s Sparrows from various sources, including records from eBird (www.ebird.org), survey data from the Bird Conservancy of the Rockies (formerly Rocky Mountain Bird Observatory), and observations by U.S. Forest Service biologists and numerous Colorado birders. After hiring Aaron Yappert, an expert birder, to assist with fieldwork, we visited 37 potential breeding locations across the state where Brewer’s Sparrows had previously been reported. This included 20 high-elevation alpine sites and 17 lower-elevation (6,000-9,000 ft) sagebrush sites. At each site, we surveyed for birds, and if present, we then recorded singing males and captured them to get measurements, photos, and genetic samples. Altogether, we recorded songs of more than 160 males and captured and collected data on 40 males in each habitat type. We found Brewer’s Sparrows at 12 of the 20 alpine sites we visited. It was both exciting and odd to find this species normally seen in sagebrush in large patches of alpine willow and krummholz at 12,000 ft! Other birders and volunteers also confirmed the presence of Brewer’s Sparrows at 6 other alpine sites.
When will we know?
We will finish analyzing and comparing genetics, measurements, songs, and photos between alpine and sagebrush Brewer’s Sparrows this fall and winter, so look for more information in spring 2022. Regardless of what the answer is, this project will help Colorado Parks and Wildlife better understand the taxonomy, distribution, and ecology of one of our high-priority non-game species and solve a nearly century-old question about Colorado birdlife. If they indeed are Timberline Sparrows, we will undoubtedly be looking for assistance from capable and adventurous birders interested in helping document their distribution and abundance in mountain ranges across Colorado.
Tune into the Terry Wickstrom Outdoors – 104.3 The Fan on Saturday, October 23, 2021, to hear a boots on the ground account from Colorado Parks and Wildlife’s avian researcher, Brett Walker.
Article by Brett Walker. Brett is an avian researcher for Colorado Parks and Wildlife. Video produced and filmed by Jerry Neal. Jerry is the senior video producer and media specialist for Colorado Parks and Wildlife.