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Study finds nearly one bird per day dies in collision with campus buildings during migration season

Omar Yossofzai, a fourth-year biology student, organized the U of T Scarborough portion of a massive North American study on migratory bird collisions. (Photo by Ken Jones)

Omar Yossofzai grew up in an urban area surrounded by buildings, but he didn’t fully appreciate their impact on bird mortality until he took part in a large North America-wide study on migratory bird deaths.   

“It was kind of stunning to see dead birds on the ground,” says the fourth-year biology student who organized the U of T Scarborough portion of the study.  

Yossofzai led a group of 20 undergraduate students over a 21-day period during fall migration to monitor six buildings across campus and collect birds that died colliding with windows. U of T Scarborough was one of 40 college and university campuses across North America involved in the project. 

He says taking part in the study was important since his team was the only one to provide data from Toronto and southern Ontario, which falls in an important migratory corridor for birds.

The study, led by Professor Stephen Hager of Augustana College in Illinois, sought to understand the effect building size and vegetation cover has on migratory bird mortality rates as a result of collisions. Researchers found that large buildings in areas of low urbanization – those surrounded by vegetation like forests and gardens – had a higher collision rate than large buildings in areas of high urbanization, like those surrounded by other buildings or parking lots.

A total of 19 bird carcasses – all non-native migratory species – were found on campus during the 21-day period. Of that number, 12 died in collisions with the Humanities Wing (HW). It makes sense that HW is a magnet for bird collisions, notes U of T Scarborough Biology Professor Jason Weir.  

“It’s a large building next to an area of low urbanization with lots of vegetation, so naturally it’s a hotspot for birds, especially migratory birds,” says Weir, who supervised Yossofzai and whose fourth-year ornithology class participated in the project.

That’s not to say greater urbanization in general doesn’t have an effect on bird collisions, adds Weir. More buildings, especially large ones, increase the overall risk of a collision. Rather, he says the take home message should be that all large buildings, but particularly those in areas of low urbanization with vegetation coverage, should adopt better conservation practices.

“Toronto is an important place to consider because even though it’s urban, we have a lot of natural vegetation with extensive amounts of forested areas in an urban setting, and it’s in a migratory corridor,” he says.

It’s estimated that nearly 1 billion birds die annually in North America as a result of colliding with building windows. Since the 1970s Weir says there’s been a sharp decline in boreal forest bird populations. While climate change and loss of winter habitat in central and south America are factors, he says what’s happening when these birds migrate could be a major factor in driving their numbers down.  

“Human-caused mortality on migratory birds is astronomical,” he adds.

In addition to building collisions, house cats also have a huge effect on the migratory bird deaths, notes Weir. Past studies showed that house cats are responsible for as many as 4 billion bird deaths every year across North America.

He says practices such putting decals on the outside of windows every few feet and turning out lights or lowering blinds during early morning and late evening, especially during migration, are good starts. Keeping cats inside, or at the very least putting a bell around their neck, can also go a long way in reducing bird deaths.

“We need to do more about it, especially with cats but also window collisions,” he says, “Any conservation steps that we can take to mitigate the mortality rate would be very helpful.” 


© University of Toronto Scarborough