It’s one of the small ways in which many people choose to commune with nature. But a new Canadian study says the practice of using bird feeders may be having the opposite of its intended effect.
The study, led by the University of Alberta grad student Justine Kummer is called “Bird feeders and their effects on bird-window collisions at residential houses”. It was published recently in the journal Avian Conservation and Ecology.
The study examined 55 windows at 43 residences in the Edmonton area. Researchers asked homeowners to record collisions between the windows and birds and found a decided pattern: with homes that had bird feeders present there were 94 reported collisions. Windows not located near the presence of a bird feeder reported just 51 collisions.
Kumer, however, cautions against drawing a straight line in the data, saying other issues such as vegetation and where a feeder is located may also be at play.
“We’ve determined that the presence of a bird feeder does indicate collision risk, but there are other factors involved,” she said. “The general public enjoys feeding birds in their yard, but they want to know how to do so safely. Homeowners can certainly reduce some window collision risk by altering feeder placement.”
So what exactly can bird lovers do to prevent these accidents? An article in Cornell’s Citizen Science blog says there’s a magic number: put your bird feeder within three feet of the window, or more than thirty feet away. The reasoning behind the numbers is that a feeder placed close to the window doesn’t allow a bird to build up enough speed to harm itself in a collision. Place it five metres away, cautions the article, and the likelihood a window strike ending in a fatality rises sharply.
Kummer’s study follows on the finding of another University of Alberta study from wildlife ecologist Erin Bayne that found that putting a bird feeder around your house approximately doubles the chance that a bird will strike your window. And Bayne said the collective mass of feeders is adding up to a real problem.
“If you multiple simply the numbers of residential structures that exist in North America by these collision rates — even though they’re low, and they’re still really low compared to some of the big high-rise buildings in major urban centers — it might even be one bird a year, or half a bird per year,” she said. “But there are so many houses, that adds up pretty darn quick.”
The numbers on how many birds die each year from collision with windows is notoriously tough to pin down, notes the BBC. The oft-quoted figure is a billion, but that figure represents the top end of an educated guess made by biologist Daniel Klem in the Journal of Field Ornithology way back in 1990. The U.K.’s British Trust for Ornithology estimates that a third of the 100-million birds that strike windows each year result in fatalities.
A 2013 study from An Environment Canada said that that more than 270-million birds are killed every year in Canada from human-related activity. But bird feeders, at an estimated 25-million deaths were nowhere near the worst killer on the list. That would be cats, which kill an estimated 200-million birds every year.