Northern harriers fight for survival

In a wetland near Boulder Reservoir, two courageous northern harriers have been fighting the battle of their lives.

On May 26, Boulder Parks Recreation volunteer wildlife monitors Gretchen and Peter Ridgeway watched an adult male strafing a marauding coyote.

“After several acrobatic leaps at the harrier, the coyote seemed to have enough of this bird and turned to leave,” said Peter. “However, the harrier was clearly not finished. He landed squarely on the coyote’s back with talons extended, and the coyote left the area.”

But throughout June, volunteers reported seeing no further evidence of incubation or nest provision at this particular site.

Though the dark female helped to chase the coyote away, the nest apparently failed a week or two later. Peter Ridgeway photo.

Every summer, nest monitors observe coyotes stalking ground-nesting harriers, and nearly every summer we lose one or more nests. In July 2015, a female harrier lost her mate, and monitors watched from a distance as a pair of coyotes dodged her strafing flights and carried off her young.

Nest monitors observe from several hundred yards away, but they’re able to track nesting progress by watching the behavior of the adults. During incubation, the female is rarely visible except when her mate flies in, hovers, and drops a mouse or vole. When the female flies up to snatch the prey item from mid-air, we’re able to map the nest location.

By early July, the female begins to make short foraging flights of her own, and when we observe both adults bringing prey items into disparate areas of the marsh, we know that the young have walked off the nest. The chocolate-breasted youngsters take flight a week or two later.

Northern harriers, are listed as “imperiled” in the Boulder County Comprehensive Plan, with only six known nesting sites active since 2000. In summer of 2019, three nests fledged a total of 11 young.

Historically, nesting harriers were considered fairly common in Boulder County. Fragmentation of wetlands and grasslands by roads, trails, trees, and agriculture has made it harder for adults to find secure nesting sites. Proliferation of human-adapted predators, including coyotes, raccoons, red-tailed hawks, and free-roaming pets, has created an unnatural situation where ground-nesting birds struggle.

Annual monitoring of nests helps to track populations over time and identify potential threats. Boulder Parks and Recreation Department Natural Lands Program Coordinator Joy Master initiated the birds of special concern monitoring in 2004, and 20-25 volunteers participate each year.

“We started our monitoring program with the goal of making data-driven decisions when it comes to protecting harriers in their habitat,” she said. “We’re hoping to maintain these areas as successful nesting sites.”

There’s been an uptick in northern harrier breeding success as nesting habitat has been seasonally closed to public access and enhanced through prescribed burns and removal of invasive trees. To learn more about the program, visit bouldercolorado.gov/parks-rec/seasonal-jobs-volunteer-opportunities-and-internships.

Look for harriers performing their low, graceful foraging flights throughout the year. As they tilt their wings from side to side, listening for scurrying mice and voles, think back and imagine a vast mosaic of undisturbed grasslands, wetlands, and woodlands stretching halfway across the continent.

Other July events

Blue grosbeaks sing their chattering song from treetops in plains and foothills grasslands.

Monarch butterflies emerge from chrysalises and begin searching for mates.

Watch for spectacular sunrises and sunsets as the 5000-mile Sahara dust plume streams overhead.

Stephen Jones and Ruth Carol Cushman are authors of Wild Boulder County and The North American Prairie.


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