Dimming Lights at Night Can Help Billions of Migrating Birds, Says Purdue Expert

Every fall, billions of birds take to the skies across North America, and the vast majority of them travel under the cover of darkness. According to Kyle Horton, an associate professor in Purdue University's Department of Forestry and Natural Resources, roughly 70% of the continent's bird species are migratory, and about 80% of those migrants fly at night, typically lifting off around sunset and peaking three to four hours later.

On peak nights, Horton notes, hundreds of millions of birds — sometimes close to a billion — may be in the air across the lower 48 states. These birds have evolved to navigate in darkness over hundreds of thousands of years, but in just the last century or two, artificial lighting has dramatically altered the nighttime skyline.

Like insects, migratory birds are attracted to lights at night. That attraction can leave them disoriented and raise the risk of collisions, particularly with windows. To reduce these hazards, Horton recommends turning off or dimming lights between 11 p.m. and 6 a.m. Other helpful measures include pulling down window shades to limit indoor glow and switching to warmer, more orange-toned lighting.

Such steps, he says, can cut down on the attraction that draws birds toward buildings and ultimately help lower migratory bird mortality. For those hoping to observe the migration, Horton points out that hotspots can be found almost anywhere — a local park, a wooded area, or a marsh, where shorebirds and waterfowl may be seen.

Tracking these movements is challenging because the birds fly at night and at high altitudes. One of the most effective tools for quantifying their migrations, Horton says, is radar data.