The goldfinch she saw killed when it flew into the glass of a tiger’s enclosure at the Philadelphia Zoo made a deep impression on Victoria Sindlinger, though she was only 10 years old.

It’s one reason she was so horrified last year when Philadelphia reported bird deaths on a much larger scale, but from the same cause.

“I’ve loved birds for my entire life,” she said. “It was a really shocking event for everyone in the birding community.”

On Oct. 2, 2020, up to 1,500 birds died in a 3½-block radius in Center City after flying into windows of high-rises. The birds, migrating with the change of the seasons, likely hit the buildings in the predawn hours; thousands more likely died throughout Philadelphia.

One birder said at the time nothing like it had happened in the city in more than 70 years.

On the anniversary of the mass deaths Saturday, Sindlinger, now 17 and a junior in high school, stood beneath a tree in the plaza outside Three Logan Square where origami birds strung from the boughs danced in the breeze. Represented in bright-colored paper were hummingbirds, cranes, swans ... an array of species that symbolized the extent of the carnage.

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“That’s to highlight the huge diversity of birds that were lost that night and the huge diversity of birds that pass through Philadelphia,” she said.

The origami flock was her idea, a way to commemorate the deaths and remind people of the ways they can help prevent future mass bird kills. Those migrating birds, who use stars as part of their navigation, were confused by lights in the city’s buildings, said Stephen Maciejewski, 71, a retired social worker and volunteer for Audubon Pennsylvania.

“It was a combination of weather, of low clouds, rain, and the birds come through in waves, and that was a big migration day and the weather kind of pushed them down,” he said. “Once they were down they were all over the place.”

Along with the lights, reflections could have tricked the birds into thinking trees were inside the buildings, and indoor atriums could have also drawn them.

In the past year, organizations devoted to birds have introduced Lights Out Philly, which encourages people to protect migrating birds by turning off inessential lights from midnight to 6 a.m., between Aug. 15 and Nov. 15. The program’s participants now include 36 commercial buildings, 43 residential towers, and six municipal buildings, according to Drexel University’s Academy of Natural Sciences.

The kill last year was a catalyst for the initiative, said Jason Weckstein, the academy’s curator for ornithology.

“It’s sort of a win-win situation,” he said. “You’re spending less money on electricity and you’re saving birds at the same time.”

Sindlinger’s exhibit included tips on how to make homes safer for birds, including applying paint, film, or paracord to windows in strips 4 inches apart to keep birds from going toward the glass.

“The reality is window strikes have been anywhere there’s glass,” said Randall Sindlinger, Victoria’s father. “Almost any piece of glass can be a problem.”

His daughter’s passion for the natural world goes back to early childhood, he said. He remembered a piece of art she drew when she was 5 of wolves and birds with “I love the earth” written on it. She made frequent visits to the zoo, and as she’s grown, birds have become deeply important to her.

Sindlinger, who lives in West Philadelphia, had sought a way to commemorate the anniversary since early this summer, and in August settled on an origami bird display.

“I wanted something that would evoke the idea of spirits,” she said, “sort of suspended in space.”

The Delaware Valley Ornithological Club provided hundreds of dollars for paper, thread, and waterproofing to protect the paper birds.

As recently as 10 days ago, it was unclear if she would be able to find a place to host the display. But the management at the building was supportive, she said, and it allowed her to hang the birds, made by her and six other families in the area, near where so many died.

The public space at 18th and Cherry Streets is a small sanctuary for wildlife, she said. Unlike many of Center City’s parks and squares, which are largely lawn spaces, the area has trees, bushes, even a fountain, a welcome respite for birds traveling thousands of miles in their southern migration. Near the decorated tree, Sindlinger spotted a Connecticut warbler and a hooded warbler. In the tree, she and her father spotted a tiny bat roosting.

“This place is a beautiful little haven,” she said.

» READ MORE: Philly can save thousands of birds that crash into our buildings and die | Opinion

Though last year’s bird kill was extraordinary in its scale, deaths and injuries from birds hitting windows are common , Maciejewski said. Since August, he said, he’s collected 165 killed and injured birds during walks in Center City.

And it doesn’t have to happen. The National Audubon Society encourages developers to use bird-safe glass, which uses fritting, silk-screening, or ultraviolet coating that alters glass’ reflectivity in a way that birds can see it.

“All the architectural schools, all the design schools are responsible for creating this nightmare, this death trap for birds everywhere.” Maciejewski said. “That has to change.”