Brewer’s sparrow research seeks to solve 100-year-old mystery

Photo courtesy Colorado Parks and Wildlife

A male sagebrush Brewer’s sparrow sings his distinctive “buzz and trill” song, described as one of the most complex among North America’s songbirds. There are about 600,000 Brewer’s sparrows living in Colorado.

 

Wake up early one May or June morning and get yourself to a sagebrush meadow. If you’re lucky, you’ll hear a cacophony of Brewer’s sparrows in full throat, singing one of the most complex songs among North American songbirds. 

“It’s alive and it’s spectacular,” said Colorado Parks and Wildlife avian researcher Brett Walker.

Walker is about halfway through a yearlong study of the Brewer’s sparrow, an otherwise nondescript brown and gray migratory songbird that weighs in at just 10-11 grams. The males’ (only males sing, which is common in North America) “long” songs – described as “buzzes and trills” – can last 10 seconds. There are about 600,000 Brewer’s sparrows in Colorado; they typically migrate to northern Mexico and southwest U.S.

There are two known subspecies of Brewer’s sparrows. The sagebrush subspecies, the Colorado variety, lives almost exclusively in sagebrush ecosystems between 3,000 and 9,800 feet. The timberline subspecies typically lives above 11,000 feet in the Canadian Rockies and northwestern Montana. But as early as 1914, birders have reported sightings of the Brewer’s sparrow in the gnarled low brush in Colorado’s high alpine in locations such as Berthoud Pass, Mount Evans, Guanella Pass and the Flattops Wilderness. 

So which subspecies is living in Colorado’s alpine tundra?

Walker and birder assistant Aaron Yappert spent about six weeks in the field this past spring and summer gathering information to solve the mystery of the high-altitude singers. Of the possible theories, Walker said they could be sagebrush birds that breed lower early in the season then in drought years go higher and breed again (called itinerant breeding). They could be timberline sparrows who came a long way south. Or – least likely but most exciting, Walker said – they could be a new subspecies altogether.

To find out, Walker and Yappert visited 37 potential breeding sites – 20 high-elevation sites and 17 lower sagebrush sites – to gather data. They discovered Brewer’s sparrows at 12 of the 20 alpine locations, around 12,000 feet high. They recorded the songs of more than 160 males. (Not only do both subspecies have a unique song, Walker said, but individual males can be identified by their own song.) 

The researchers captured 40 male birds in both sagebrush and alpine habitats. Each bird was photographed, weighed, measured and banded. Feathers and tiny samples of blood were taken from each for – most important – DNA analysis. Then each bird was released back to his habitat.

The closest the researchers came to Salida was a sagebrush area on the south side of Poncha Pass and an alpine site on Cumberland Pass. Walker said he really wanted to get up to Billings Lake (north of North Fork Reservoir) but ran out of time. 

Why study only males?

“They’re a lot easier to catch,” Walker laughed. The males are very territorial (females not so much), so when Walker and Yappert would broadcast recordings of other males’ songs, males in the vicinity were quick to react. It was helpful, too, he said, to keep the sample to one sex so they could compare apples to apples.

It will take the researchers several months to analyze their data. They’ll compare DNA, songs, photos, measurements, etc., and should have results next spring.

But why should we care about what’s happening to this tiny brown songbird?

“We’ve been surveying wildlife in this country for well over 100 years,” Walker said. “A new discovery (of a new subspecies) would be quite significant.” That discovery inevitably would spur more study. 

If the research shows the alpine nesters are “sagebrush birds doing weird things,” Walker said, it would tell scientists that the Brewer’s sparrow population is larger than previously thought and therefore less of a conservation concern.

Even though the Brewer’s sparrow is the most abundant songbird of the sagebrush ecosystem, its population in Colorado has declined about 2.9 percent annually from 1968 to 2012, according to the Second Colorado Breeding Bird Atlas. 

The sagebrush ecosystem is the largest interconnected habitat type in America, one of our last remaining wide-open spaces, according to the U.S. Fish and Wildlife Services. But it’s under threat by habitat loss and fragmentation through livestock grazing, residential and energy development, agricultural conversion and spread of invasive plants like cheatgrass that can serve as fuel for wildfires.

If their research findings show the birds found in the Colorado alpine are the timberline subspecies, that would indicate a “huge range extension,” Walker said, meaning the timberlines are breeding much further south than previously known.

“Colorado has lots of suitable alpine willow/krummholz habitat at treeline similar to what they use further north,” Walker said.

Walker, who earned his doctorate in fish and wildlife biology from the University of Montana-Missoula, is headquartered in the Grand Junction CPW office. He said anyone spotting a Brewer’s sparrow in an alpine region next spring or summer is invited to post their findings on the Cornell Lab of Ornithology ebird.org site or on the eBird app. Walker said he used eBird to locate some of his study sites this summer. He’s also available by email at brett.walker@state.co.us.

For more information, and to listen to a recording of the Brewer’s sparrow lovely long song, visit coloradooutdoorsmag.com and search for Brewer’s sparrow.