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A recent study by �ʹ�����’s University researchers reveals that even common city-dwelling birds, which are equipped to cope with human-altered environments, are not protected from ongoing population declines being seen across North America.

Avian population declines in North America have resulted in a loss of an estimated 3 billion individual birds since the 1970s, reflecting the current global biodiversity crisis. While even seemingly abundant species have suffered declines, the factors that influence each species’ vulnerability to decline are not well understood.

The findings of the study, conducted by then-undergraduate student Julianna Petrenko (now a master’s student at �ʹ�����’s Biology), with supervision from Fran Bonier (Associate Professor, �ʹ�����’s Biology), along with collaborators Rachel Fanelli (former master’s student, �ʹ�����’s Biology), and Paul Martin (Associate Professor, �ʹ�����’s Biology), were recently highlighted in an article published in , a journal of the Royal Society.

It concludes that although the factors that influence a species’ vulnerability are not well known, how well a species tolerates urban environments is not one of them.

The result wasn’t what the team was expecting.

“We know we're losing a lot of birds and though our study did set out to explain some of the variation in the trajectories we didn't find a reason why some species are more vulnerable than others,” explains Petrenko, the lead author of the article and a member of The Bonier Lab. “Coming in, we expected species that thrive in cities, and are generally better suited to many different conditions, would be doing better, but our results show that they aren't guaranteed protection. They were just as likely to be increasing or stable or declining as birds that completely avoid cities, which is surprising.”

This is what’s known as a negative finding, but it was equally as important in providing guidance for future studies.

“It was such a surprising result, and it's one of the rare cases where a completely negative result – like, absolutely no relationship – is still super important,” Dr. Bonier says. “That's unusual in science in general, where a finding of absolutely no relationship is quite important and publishable. This finding tells us that no, just because you see a lot of birds in the city, it doesn’t mean their populations are doing well.”

Massive amounts of data

The study looked at 397 North American bird species with data gathered from 1993 to 2019. It is the first to test for an association between a bird species’ ability to cope with urban environments and overall population trends.

With such a massive amount of data, maintaining the highest level of organization throughout the process was paramount. Inspecting metadata, making sure there are not duplications or misplacements, and then checking again and again. It meant countless hours of work for the team to ensure that everything was accurate. The rigour was extremely high but as Dr. Bonier explains, “a study’s only as good as the quality of the data.”

Pandemic shift

Petrenko’s line of research for her undergraduate honours thesis was influenced by the pandemic. Fieldwork is an important form of information gathering for biologists but as the pandemic took hold, and lockdowns required people to stay home, the members of the Bonier Lab had to alter course.

“Due to the pandemic we shifted to a lot of these sorts of projects, that I always appreciated were powerful, these big comparative studies using huge amounts of public data. This shift created a new focus in my lab, where we’re tapping into the power of these data projects to answer broad, important questions,” says Dr. Bonier.