Go dark at night to help avian superhighway

By Dr. Beth Leermakers

Lights Out! Bird Migration Alert! You may have seen signs in your neighborhood encouraging people to help migrating birds by turning off non-essential lights between 11 p.m. and 6 a.m. in March through June. Peak migration is from April 22 to May 12, so now is the time to go dark.  

Millions of migratory birds soar across our Texas skies every spring and fall. Brightly lit buildings can confuse and disorient birds on their journey, resulting in deadly collisions. As many as 3.5 billion birds die from collisions with buildings every year in the United States. Light pollution makes the Dallas-Fort Worth metroplex the third most dangerous area in the U.S. for migratory birds to travel through. 

Let’s examine what makes migrating birds so special — and worth a few hours of darkness at our homes. 

Some birds are medium distance migrators, covering a few hundred miles, while others travel long distances. Hummingbirds (weighing as little as .1 oz.) are the smallest migratory birds, with one species traveling 3,900 miles between its Alaskan breeding grounds and its Mexican wintering grounds. Great bustards (up to 44 lbs.) are among the heaviest birds that fly. Asian great bustards travel more than 2,000 miles from their Mongolian nesting grounds to their Chinese wintering grounds. Closer to home, Bar-tailed Godwits nesting in Alaska fly more than 6,000 miles without stopping for food or rest to their winter home in Southeast Asia, Australia or New Zealand. 

Many (350) species of North American birds undertake long-distance migration, traveling from breeding ranges in the U.S. and Canada to wintering grounds in Central and South America. Migrating birds tend to follow regular routes on their biannual flights. 

Bounded on the west by the Rocky Mountains, the Central Flyway is an “avian superhighway” that runs through Texas, Kansas, Colorado, Wyoming and Montana, extending into the Great Plains. More than 50 percent of North America’s migratory waterfowl use this flyway, as well as many shorebirds like the Snowy Plover.  

Migrating birds typically fly 15 to 55 miles per hour, covering 15 to 600 miles or more per day. Most birds travel at night, when there are fewer predators and colder air temperatures reduce the risk of overheating. Night flying is riskier than it used to be, with well-lighted buildings and communication towers attracting and disorienting birds. 

Before migrating, birds enter hyperphagia — bulking up on food for several weeks to store fat that will fuel their long, demanding journeys. A blackpoll warbler doubles its body weight before making the 70-80 hour, 2,000-plus mile nonstop transatlantic flight between their nesting grounds (in the northeastern U.S., northern Canada or Alaska) and South America. 

Why do birds undertake such an arduous journey? They migrate to follow resources, leaving areas with scarce or declining food and nesting locations to reach regions where they are abundant or increasing. Birds who nest in the Northern hemisphere typically migrate north in spring to benefit from growing insect populations, budding plants and plentiful nesting sites. As winter nears and food sources decline, they head south again. While avoiding the cold plays a role, many birds — like hummingbirds — can survive freezing temperatures if enough food is available. 

A combination of factors — changes in day length, lower temperatures, shifts in food supplies and genetic predisposition triggers migration. Migratory birds kept in cages undergo zugunruhe (migratory restlessness) in the spring and fall, repeatedly fluttering toward one side of their cage. 

Migratory birds often travel the same route every year with little deviation. Some species, like waterfowl and cranes, follow specific migration routes linked to key stopover sites that offer essential food. In contrast, smaller birds often migrate in wide fronts, with eBird data showing many take different spring and fall paths to take advantage of seasonal patterns in weather and food availability.

Young birds frequently make their first migration on their own, finding their winter home without ever having seen it before. The next spring, they return to the exact location where they were born. How do they navigate so successfully? 

Scientists don’t fully understand birds’ navigational skills, which involve several senses. Birds can get directional information from the sun and stars and by sensing the earth’s magnetic field. The position of the setting sun and landmarks seen during the day also provide navigational guidance. Some birds, such as homing pigeons, also rely on their sense of smell. 

Soaring to 

Remarkable Heights

Bar-headed geese are the highest-flying migratory birds, reaching altitudes of 16,000 to 20,000 feet while flying over the Himalayas between India and Mongolia. At those high altitudes, where PO2 is approximately half of that at sea level, there’s less oxygen available to support their metabolism. 

These high-flying geese are more likely to be disoriented by a shooting star than a cell tower. 

To learn more about protecting migratory birds closer to home, visit tcatexas.org/lights-out-dfw.