The same factors that draw birds to your backyard may also contribute to their death by window, suggests a recent study.
University of Alberta masters student Justine Kummer published a study in The Condor this week on factors related to bird-window collisions in Alberta.
The study builds on a similar one done by co-author and U of A biologist Erin Bayne in 2012.
"Recent estimates have said up to 22 million birds (in Canada) are dying from collisions with windows of our houses each year," Kummer said, citing a conclusion of the 2012 study.
While previous studies have identified several ways where humans raise the risk of bird deaths, Kummer said that this was the first to compare many of them to determine their relative importance.
Kummer recruited 1,315 Albertans, mostly from the Edmonton and St. Albert region, through the Birds and Windows Project in 2013. Kummer had them monitor their homes for evidence of bird collisions each day for (ideally) 28 days. She and her team also used Google Earth to determine general landscape features of each monitoring site, such as distance to the nearest tree stand. The team took the 930 collisions recorded, 102 of which were fatal, and ran them through several analytical models to determine which factors were most associated with collisions.
The team found that time of year and home location were the most significant factors when it came to what caused a bird to hit a home. Birds were six times more likely to hit windows at rural locations during the fall than they were to hit them at urban ones in the winter.
Tall trees were another risk. Birds strikes were 3.6 times more likely to happen in yards where homes had trees that were taller than two stories compared to those that had no trees. Having a bird feeder raised collision risks by 1.7 times.
Happy home, deadly home?
Kummer said she wasn't that surprised by these results.
"These are things that are attracting birds to a house," she said, and the more birds you have, the better your odds of having a collision.
We get more collisions in the fall as migration brings more birds to our homes, she explained. Rural homes have more trees, which means more habitat and birds. Winter might reduce collisions because the birds that stay here tend to stick around the same yards, making them more familiar with hazards such as windows.
St. Albert's tall trees are great places for birds to find food and shelter and are also often at the same height as windows, which makes them risk factors as well.
The study found that bird feeders raised the risk of collisions even for birds that didn't use them. The study suggests that this could be due to feeders often being in yards with lots of vegetation or other attractants, such as bird-baths.
Kummer suggested that protecting natural areas and keeping yards small could help reduce the risk of bird collisions, as would repositioning your bird feeder. Removing trees could help, but few people are willing to do that.
You can reduce the risk caused by your bird feeder by putting it within three feet of your window (so the bird doesn't have room to get up to ramming speed when it flies away from the feeder) or more than 10 feet away (so it has room to steer), said Dave Cleary of Edmonton's Wild Birds Unlimited.
"A lot of bird fatalities are house sparrows," he noted, which frequent feeders and spook easily. The reflections caused by windows confuse them, causing collisions.
Black stickers help break up a window's reflection, but also obscure your view through it. Cleary suggested using transparent UV-reflective ones instead, as the birds will see the UV light.
If you find a concussed bird that's still alive, Cleary suggests gently picking it up in a tea towel to keep it warm and leaving it in an open box off the ground so it's safe from cats.
The study is available at www.aoucospubs.org/loi/cond.