Billions of birds are preparing for (and even already embarking on) their cool-weather exits. Isn’t it intriguing how many migratory birds seem to quietly disappear as summer fades away? Turns out most of us humans tend to miss these massive avian departures because they typically happen at night. According to the Audubon Society, 70% of terrestrial recurring birds (aka birds that spend much of their time nesting or foraging on the ground) in North America are migratory, and 80% of them travel after dark.
While there’s still much to learn about why birds take off after sunset, researchers have a few decent explanations:
The atmosphere is more stable after dark, making it easier for birds to chart a smooth and steady course — especially smaller species that move more slowly
Darkness shields vulnerable birds from predators and provides a safer voyage
Cool nighttime temperatures keep these hardworking birds from overheating
Most importantly, birds rely on the stars and moon as GPS, helping them navigate to their warmer destinations
Unfortunately, we humans and our penchant for artificial outdoor lighting can throw off those avian navigation systems. Light pollution can confuse migrating birds, causing them to stray off course and even collide with buildings and structures; some birds become so disoriented they exhaust themselves to death trying to get back on track. To combat this problem, organizations like the Audubon Society and DarkSky International promote the Lights Out Program, which encourages building owners to reduce light pollution, though you don’t have to be a real estate mogul with a flair for excessive lighting to take part. Simply turning off or dimming exterior lights on your home or business between 11 p.m. and 6 a.m. during migration seasons can support traveling birds. When should you start?
Fall migration begins August 15 and ends November 30
Spring migration runs from March 1 to June 15
While flipping the switch on your porch lights might seem pretty minor, it’s a small move that can support birds in a big way. A 2019 study revealed North America’s avian populations have declined by nearly 3 billion birds over the last 50 years — an extensive loss that particularly affects many backyard feeder species like Dark-eyed Juncos, Red-winged Blackbirds, and other songbirds. Light-reducing efforts give birds a fighting chance at departing and returning safely, and may be one tool at combating that population slump.
Art note: “Bird with autumn foliage” by L. Prang & Co, 1873, courtesy of the Library of Congress.