As fall bird migration nears its end in New York City, a troubling trend may be emerging: preliminary evidence suggest that more avians collided with buildings this season compared with last autumn.

NYC Bird Alliance surveys suggest that collisions are up citywide and that it has proved to be a “particularly bad” autumn for collisions. While spring 2024 showed fewer collisions than in 2023, about 60-75% of such accidents occur during fall migration, which peaks from early September to October.

Rita McMahon, director of Wild Bird Fund, said that volunteers and Good Samaritans brought a daily average of 60 to 70 injured migratory birds to the rescue organization during peak fall migration in October.

The spring always sees fewer accidents because there aren’t as many migratory birds as in the fall, McMahon explained.

“All the birds going up in the spring are going up to mate and have babies and follow the insects,” McMahon said. “In the autumn we have returning adults and newer adults, so fall is much larger than spring migration.”

Fall migration also has more accidents, “because this is the first time a young bird might come through New York and doesn’t know glass and hasn’t learned about it.

“We have to learn glass as a child. Everyone at one point or another has walked into glass,” she continued. “It’s very hard on the young.”

New York City is dangerous for migratory birds as they are at risk of accidentally flying into tall buildings’ reflective glass surfaces. The skyscraper-laden metropolis is located on the Atlantic Flyway, an area through which migratory birds fly between locales as far north as the Article Circle, south to Latin America.

As numerous migratory species, notably most songbirds, fly at night, the combination of bright light and reflective glass buildings can prove deadly, attracting and disorienting them. A bird might see reflections of the sky or plants, fly into a window at full speed, loose consciousness, and plummet to the ground.

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Dozens of volunteers peruse the sidewalks near shiny skyscrapers every morning, counting the dead and transporting the injured living to the fund in paper bags.

Andrew Farnsworth, a visiting scientist at Cornell University’s Lab of Ornithology, said that researchers didn’t have all the numbers yet, but it seemed that earlier in the fall, there was up to a 20% increase. This belief is based upon the information available thus far.

“We know that the estimate in New York City – close to 250,000 birds dying in collisions every year – is definitely an underestimate, no question,” Farnsworth said.

Katherine Chen, senior manager of community science and collision reduction at NYC Bird Alliance, said that several factors present difficulties in making definitive statements about an uptick in collisions this year. The season hasn’t yet ended, so there isn’t definitive data, and numerous factors affect how collisions are detected – among them random variation.

The aggregate number of estimated bird collisions and resulting deaths is calculated using data from on-the-ground volunteers who count the injured and dead, and then extrapolating what this sample means overall given total migration numbers and prior mortality statistics.

“Just anecdotally, this does seem to be higher this year compared to what they have seen last year, at least,” Chen said.

“We started off the season with a pretty heavy week, which usually starts late August, early September, and this year was a pretty startling week to start off with,” Chen said. “We found over 100 birds during that first week, which isn’t something that we’ll typically find there.

“Again, there are a lot of factors that go into how many birds you find, and we are monitoring more locations this year than we were last year, so that could be another factor.” But, Chen said, “we didn’t find over 100” in fall 2023.

One reason why advocates might be seeing increased collisions: data indicates that more migratory birds are flying through New York, with more than 9.7 million passing over Manhattan so far this fall, compared with about 9.5 million in 2023.

This data, from BirdCast, uses the US weather surveillance radar network to track nocturnal bird migration. Farnsworth, who co-founded BirdCast, said it was normal for the number to fluctuate season-over-season.

Jessica Wilson, NYC Bird Alliance executive director, said that the bird collision crisis – the group estimates that more than 1 billion birds die every year in the US from glass collisions – could be stopped if cities and buildings took just a few steps.

“Collisions with windows represent a major, but fixable, threat to wild birds,” Wilson said in a statement. “Simple, commonsense solutions can prevent many of these deaths.”

Some city buildings, Wilson noted, voluntarily turn out needless lights at night, preventing reflections that can fatally confuse migrating birds. Other buildings have put in bird-safe glass.

“But voluntary actions are not enough: millions of buildings still pose deadly risks to birds due to artificial light at night and untreated glass.”

A bill aimed at preventing light-related bird collision deaths is pending in New York City.