To have a stable population of living creatures, the number of births has to equal the number of deaths. It doesn’t matter if that creature is a human or animal or if the animal is a bird, reptile or mammal. If the birthrate doesn’t replace the death rate, the population will decline. If more are born than die (as is now the case with humans) the population will increase.

Birthrate verses death rate is controlled by many things and for most migratory birds a stable population is maintained by them producing large clutches of eggs when they are nesting. Despite big clutches of eggs and the resulting high birth rates, the population of many migratory birds are decreasing. In many cases, it’s the migration which is the killer.

Most migrants couldn’t survive without migrating from their summering area to their wintering grounds. But that migration, often thousands of miles, is the most perilous time of their lives. Any number of natural or unnatural calamities can occur. Migrating birds can be caught in storms, lost in fog over the Great Lakes, killed by predators, starve or simply run out of energy.

They can be chopped up by wind energy farms, struck by flying airplanes or collide with tall buildings. In fact, an estimated 600 million birds die from colliding with buildings every year in the United States.

Scientists at the Cornell Lab of Ornithology recently published new research highlighting city lights at night as a contributing factor to bird collisions with windows and buildings. They also ranked the metro areas where birds are at greatest risk of being attracted to and/or disoriented by lights and crashing into buildings. The risk comes from a combination of the amount of light produced and the geographical location of the cities. The research combined satellite data showing light pollution levels with weather radar that measures bird migration density.

The most dangerous American cities for birds overall when looking at both fall and spring migrations are Chicago, Houston, and Dallas. Because many birds take different migration routes during spring and fall, rankings of the most-dangerous cities change slightly in the spring and fall migration seasons.

During spring migration, billions of birds migrate through the central United States between the Rockies and Appalachians, so it’s not a big surprise that cities in the middle of the country are among the most dangerous during fall and spring migrations. Greater spring migration along the West Coast also puts Los Angeles on the spring’s most dangerous cities list. Fall bird migration tends to be more intense along the heavily light-polluted Atlantic seaboard, which is why four eastern cities make the “top 10” list during autumn.

In our area, we have our own brand of “northern lights.” These have nothing to do with the aurora borialis which comes from electrically charged atmosphere over the Arctic. Ours comes from the lights from Chicago glowing to our north. If we can see it, so can the birds and for the birds, it can be fatal.

The 10 Most Dangerous American Cities for Birds during FALL Migration: 1) Chicago, 2) Houston, 3) Dallas, 4) Atlanta, 5) New York, 6) St. Louis, 7) Minneapolis, 8) Kansas City, 9) Washington, D.C., 10) Philadelphia. The 10 Most Dangerous American Cities for Birds during SPRING Migration: 1) Chicago 2) Houston 3) Dallas 4) Los Angeles 5) St. Louis 6) Minneapolis 7) Kansas City 8) New York 9) Atlanta 10) San Antonio.

Chicago, Houston, and Dallas are uniquely positioned in the heart of North America’s most trafficked migration corridors. This, in combination with being some of the largest cities in the United States, make them a serious threat, regardless of season.

Now that it’s known where and when the largest numbers of migratory birds pass heavily lighted areas it’s hoped this information can help spur extra conservation efforts in these cities. For example, the Houston Area Audubon Society uses migration forecasts from the Cornell Lab’s BirdCast program to run “lights out” warnings on nights when large migratory movements are expected over the city.

Though less common, an estimated quarter-million birds die from collisions with houses and residences every year. Even in our area, homeowners can play an important role in stopping bird deaths. It’s simple. If you don’t need lights on, turn them off. If you need lights at night, simply close the shades or curtains! It will save energy and can make a difference, one bird at a time if the practice is widespread.