We know that waterfowl like geese migrate at night, but did you know that songbirds do too? Beneath Western Colorado’s vast, star-strewn skies, migratory birds like Warbler’s, and Swainson’s Thrush embark on a breathtaking odyssey, their wings slicing through the night during peak migrations in May and September, from 10 p.m. to 2 a.m.
“This time of year, in Western Colorado, the skies are filled with warblers,” Zach Hutchison of Audubon Rockies reported in the (Telluride) Daily Planet (May 10, 2025). These insectivores—warblers, flycatchers, vireos— navigate thousands of feet above, guided by the North Star and constellations, their instincts decoding stellar patterns with astonishing precision, (per Cornell Lab 2019). The moon and Earth’s magnetic field refine their celestial compass, steering them across continents.
Nocturnal artificial light drowns cosmic beacons and lures these feathered voyagers into artificial light. Imagine a warbler, drawn off course by artificial light, crashing into a window or circling a light source to exhaustion, its journey silenced. When birds encounter excessive light, they become disoriented—a phenomenon called "light entrapment.”
A 2019 Cornell Lab study estimates 1 billion U.S. birds die annually from collisions, driven by light pollution’s glare. During peak migration, radar studies detect up to 420 million birds crossing Colorado in a single night. The Black Swift, which nests exclusively behind our mountain waterfalls, and the Virginia's Warbler, with 90% of its breeding population dependent upon Colorado habitats, are among those at risk. Here in Colorado, artificial light can draw migrating birds off course by up to 5 miles, increasing mortality by 30-40%.
A May 10, 2025, Telluride Daily Planet article notes that 80% of Western Colorado’s migratory birds travel at night. This article also mentions that one-to-three-story structures, common in the San Juans, account for 44% of bird mortality. It’s not just high rise buildings that attract birds. Western Colorado loses an estimated 3.5 to 5.8 million birds annually from building collisions, with 82% occurring during migration. Even more alarming, North American bird populations have decreased by nearly 3 billion birds since 1970—that's one in every four birds, gone.
Our six native swallow species—Cliff, Barn, Tree, Violet-green, Bank, and Northern Rough-winged—are particularly vulnerable. A single Cliff Swallow colony consumes over 50 tons of insects in one breeding season, providing natural pest control for our farms and communities.
The Western Slope Dark Sky Coalition (WSDSC) battles this tragedy, pushing for San Miguel County to become a Dark Sky Reserve. With lighting codes instituted in 2021, a $5,000 county grant, and 70 hours of state consulting, WSDSC’s mission protects these winged voyagers. Join WSDSC’s “Lights Out” campaign. Dim non-essential lights during migration. Use lower lumen bulbs (under 800 lumens) and warmer color temperatures (below 3000K).
Daytime crashes can be mitigated by applying window stickers 2 inches apart and hanging paracord curtains.
Support WSDSC’s Dark Sky Reserve at westcoloradodarksky.org and track bird migration at birdcast.info.
Your actions matter. By dimming our lights, we rekindle the stars, ensuring these celestial navigators soar safely, their melodies resounding throughout our canyons.