On January 31, Toronto became the first city in the world to implement protections for migratory birds by controlling light emissions, through public education, and bird rescue. Bird deaths, especially during spring and fall migrations when when millions of birds are moving generally north and south (birds also migrate east and west), occur when birds are distracted by bright lights and glass windows during evening hours. It’s estimated that upwards of 10,000 migrating birds are killed each year in Toronto alone. The program encourages businesses to turn out their lights during spring and fall migration periods to attempt to reduce bird strikes.
Light pollution and the effects on wildlife has become a hot topic of research, study, and debate over the past few years, not just in North America, but all over the world. Bird strikes against windows have been studied and recorded since the 1930s, bird strikes against aircraft has been studied for years and is ongoing. Other man-made structures causing bird mortality are wind turbines, communication towers, and powerlines, not to mention other causes of mortality such as collisions with automobiles, ingestion of poisons, pesticides, insecticides, and illegal shooting.
All these hazards combined exact a heavy toll twice each year on migrating birds from sparrows to eagles. Age, size, and health of the individual bird does not seem to play a role in determining the probability of striking an object or dying as a result of a strike. About 50% of bird strikes cause direct mortality. An unknown number of the remaining 50% will survive while the rest will die from various causes, external or internal injury, increased susceptibility to predation due to injury, starvation due to injury (the inability to feed or catch prey), disorientation resulting in a second strike, etc.
Each city is different in terms of number, height, arrangement and distribution of buildings, proximity of the city to migratory flyways, weather conditions, and a host of other factors. While extrapolating from studies conducted in cities with similar configuration can be a starting point, to be accurate, studies need to be conducted in each city to develop effective management plans.
A 1990 study by Daniel Klem, Jr. Journal of Field Ornithology. 1990. 61(1):120-128 states that in the U.S. alone, Klem estimated 97 – 976 million birds are killed each year in window strikes. Other estimates range from 3 million and up. Klem’s study was conducted using residential buildings rather than commercial structures and his estimate was 33 deaths per year at a single dwelling. While Klem looked at the numbers of strikes and resulting mortality, his study looked at preventative measures (silhouttes, wind chimes, flapping cloth) and their success in deterring birds from windows. He found that a single object placed on a window is not enough to prevent bird strikes. The window must be uniformly covered by objects on or close to the window 5 – 10 centimeters (2 – 4 inches) apart.
Birds do not recognize glass as a barrier, so one or two decals on the window will not let them know to be careful. If the decal is of a hawk or owl silhoutte, they will just try to go around and hit the window anyway.
When I worked in the Zoology Department at the Denver Museum of Natural History (now the Denver Museum of Nature and Science), we received a large supply of bird specimens from local area residents picking up bird kills outside their windows. While unfortunate, this was a very good source of data in terms of species, distribution, age, plumage, etc. that would otherwise have been difficult to collect and was a better use of the carcass than taking it to the landfill.
Other cities around the world should take Toronto’s lead. Besides reducing the number of migrants killed, turning off lights will save a bundle of energy. Who said wildlife wasn’t useful for anything?