Homeowners vs. Birds: the Depressing Probability of Window Collisions
Erin Bayne got to thinking about how often birds collide with windows because, at his own home in suburban Edmonton, they seemed to be doing it regularly. Bayne is a wildlife ecologist at the University of Alberta, where he studies human impacts on biodiversity. And he’d frequently heard theories on this subject in his work with Canadian industries.
“One of the comments I often got from industry was ‘cats and windows kill way more birds than I ever do, so why don’t you leave me alone?’” he says. “There’s a general perception.”
But is that true? And what about the birds bouncing off his own windows? Skyscrapers get the bulk of the attention when we talk about the one-two punch of urbanization on some of nature’s smallest creatures (first, we raze their habitats, then we put in their place deceptively reflective high-rises). But there are a lot more windows out there on private homes than office towers. And they must have some effect, too.
In researching this question with one of his undergraduate classes, Bayne has produced some of the clearest estimates we have to date of this hard-to-measure bird vs. window phenomenon. The results, just published in the journal Wildlife Research, come from an online survey with 1,458 people in the Edmonton area. Thirty-nine percent of them said they had observed a bird-window collision in the previous year at their home, and many of them saw more than one.
On average, this data suggests that at least 1.7 birds careen into the typical home in a given year (although there was wide variation among the homes in this sample). Extrapolate that out to the entire country, and that means about 22 million birds die this way across Canada each year.
“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,” Bayne says, “but there are so many houses, that adds up pretty darn quick.”
Calculations like this are invariably flawed. As Bayne and his co-authors acknowledge in the paper, researchers are unlikely to ever convince citizen-scientists to conduct truly rigorous searches for bird carcasses around a representative sample of homes at exactly the same time (see, also, the related imprecise study of the urban bird menace from cats). But a few intriguing patterns emerged from this research that may hold up better than the specific numbers do.
For one thing, having a bird feeder in your yard roughly doubles the odds of a bird-window collision. “Putting up a bird feeder is kind of a catch-22 in a way,” Bayne says. In other words, you may be doing those birds a favor by feeding them, but you’re also luring them into the realm of your deadly windows. And Bayne suspects that bird feeder placement matters; putting it further from your home can help. So can putting it right next to your building, where birds coming and going from it are less likely to be traveling at top speed (birds are subject to the same principle as cars ramming into a parked object; the faster they’re moving, the worse the wreck).
In this survey, birds also seemed to fare poorly in relatively older neighborhoods. In Edmonton at least, the age of a neighborhood is a good proxy for something else: the presence of the kind of big, old trees that birds like to occupy. Newer subdivisions, with their scraggly saplings, just logically don’t have the same appeal.
Bayne is working on further research that will break down the relative menace from those industries pushing the window-and-cat narrative. But, for now, he tells us this: “Based on these estimates that we have, windows and cats remain two of the highest killers of birds annually. The caveat to that – something that’s very important for the public to understand – is just because a bird is killed every year, doesn’t mean it results in the most dramatic decrease to a population. Converting a forest into a parking lot has a much greater long-term effect than just killing some birds in one year.”
So, at least, you can feel better about that.