Bridget Stutchbury has a chest freezer stuffed with songbirds, a makeshift morgue that troubles her heart.

“There’s just so many in here,” says Stutchbury, a York University ornithologist, lifting the freezer’s lid in her lab and rummaging through stacked Ziploc bags. “Here’s an oriole, a grosbeak, a meadow lark, an oven bird — we get lots of oven birds.

“Look at them all,” she says. “It’s very upsetting.”

The small birds met a painful end, slamming into windows at York University. About 2,000 die this way at York’s main campus each year — part of the 25 million birds killed in window collisions annually across Canada.

Stutchbury is one of North America’s leading ornithologists. And during a quarter-century of work at York, she’s witnessed what felt like a massacre in her backyard: birds that survived long, perilous migrations ending their lives with a head-crushing thump.

An especially proficient death trap was the ground-level glass wall of the Executive Dining Room at the Schulich School of Business.

“The people dining there didn’t express any concerns,” Stutchbury says, noting the results of a student survey of the site. “But the staff working there every day said it was so depressing to hear that thunk on the window — ‘And there goes another one.’”

In October, after three years of lobbying efforts by Stutchbury and her students, York became one of the first universities to tackle the problem. It spent $90,000 to buy and install “bird-friendly” patterns on windows at five of the most deadly sites on campus.

The pattern is a simple sequence of small dots, a signal to birds that transparent glass is not an open space they can fly through. A sixth building will be fitted next spring. If the patterns reduce collisions, other buildings will get the treatment once budgets permit, says Ronald Ogata, York’s manager of renovations.

Stutchbury’s students surveyed the deadliest spots on campus by collecting dead and injured songbirds. At the Schulich Executive Dining Room, 57 had died or injured themselves during migrations this spring and last fall.

The dining room was especially deadly because birds would land in its courtyard to feed, mistake the reflection of trees and bushes on the glass wall for the real thing and fly to their deaths trying to reach them.

“Birds aren’t stupid,” Stutchbury says. “They’re not just flying into buildings because they don’t know where they’re going.”

York University isn’t an especially bad killing field in Toronto. The city stands in the path of a major migratory corridor and at least one million birds collide with windows each year. Since 2010, new Toronto buildings must include design features that reduce the chances of these accidents.

What particularly disturbed Stutchbury is that some birds found dead on campus, like the wood thrush, are listed as threatened in Canada.

“When we dissect birds that have collided, the brain hemorrhage is really obvious,” says Stutchbury, a professor of biology. “They literally have dents in their heads and extensive internal injuries. It’s like someone in a terrible car crash who wasn’t wearing a seatbelt.”

Stutchbury is 57 and grew up in Montreal. She developed a love of the outdoors as a child at her parents’ cottage in the Adirondack Mountains. Her fascination with the behaviour of birds began at Queen’s University while studying biology.

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She was working on a field project examining the nests of tree swallows in bird boxes. She lifted the lid of a box and saw two female swallows in violent combat, one of them with a bloody head ripped of feathers.

“They froze in a wrestling hold looking at me, one of them just going, ‘Please help me,’” Stutchbury recalls. In the bird world, it’s males who usually fight for territory. Stutchbury went on to do her thesis work on violence between female tree swallows when competing for nest sites.

Another behaviour she documented was the “premeditated divorce” practices of female blue-headed vireos. In her book, “Bird Detective,” Stutchbury notes that both male and female birds build the nest, incubate the eggs and feed the chicks.

Throughout this time, however, the female sneaks off when she can and secretly woos another male. When the chicks fledge she abandons her loyal partner and quickly mates with her secret lover. If she didn’t cheat on her first partner, she wouldn’t have time for a second brood, Stutchbury notes.

Her most celebrated work came while leading a research team in 2009. They figured out how to track songbirds weighing only 50 grams, too small to carry GPS tracking devices on their backs.

They placed modified light sensors called geolocators, weighing 1.5 grams, on wood thrushes and purple martins. For the first time, researchers could track individual songbirds.

Songbirds will return to exactly the same spots to refuel or breed during a migratory round trip. Half will die along the way. To analyze the data, Stutchbury’s team had to recapture the lucky few who returned with light sensors on their backs.

By analyzing the level of light captured by the sensors, and calculating sunrises and sunsets, the team determined the route the birds took, where they stopped to feed and how fast they made the trip — information important for species conservation.

The purple martins flew from Brazil’s Amazon rainforest to the Canada-U.S. border — more than 9,000 kilometres — in two and a half weeks. “We had no idea they were moving that fast,” Stutchbury says.

Most songbirds travel at night and can rest half their brain in near sleep mode by keeping one eye closed, she adds. They’ll consume all their body fat in one overnight flight and then land to refuel. They rarely live more than two years and only about half survive migration and come back to breed.

A recent study estimated the bird population in Canada and the U.S. declined by three billion — 29 per cent — since 1970. Pesticides and habitat loss are partly to blame. But the biggest menace that can be measured, Stutchbury says, is cats — they kill 250 million birds a year in Canada. Keep cats indoors, she pleads.

She raised the alarm about the rate of disappearing songbirds in her 2010 book “Silence of the Songbirds.” Still, Stutchbury believes the birds are here to stay. Passerines make up half of all birds on Earth and have shown an incredible capacity “to recover from the onslaught that we’re sending their way,” she says.

She just hopes the bird-friendly window installations at York University fill her freezer with fewer birds and specimens for her students to dissect.

“They’re yellow and red and just beautiful to look at,” Stutchbury says, examining a bag of birds. “Except that they’re dead.”