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Every morning during fall and spring migration, volunteers gather in cities across the United States to search for dead and dying birds. Their killer isn’t cats, pesticides, or BB guns. It’s glass.
“When they hit, they don’t die from a broken neck,” says Tim Jasinski, a wildlife rehabilitation specialist at the Lake Erie Nature & Science Center. “They actually die from cranial swelling. The brain is bleeding, basically.”
In some cities, especially those that are stopover sites like Cleveland due to Lake Erie, the frequency with which birds fall out of the sky can be startling. One autumn, volunteers counted more than 1,800 birds dead from collisions.
“They’re hitting, and you’re picking them up, and another one hits, and it falls on your back or it falls next to your hand,” says Jasinski, who volunteers with Lights Out Cleveland looking for birds each morning before work. “It’s just like raining warblers and sparrows. It really sucks.”
“A lot of the monitoring programs are based on finding dead birds or birds that are severely injured. We could be underestimating how big this problem really is.”
– Lucas DeGroote, avian research coordinator
On average, 600 million birds die each year in the U.S. upon striking glass. Most birds have eyes on the sides of their heads and can sense predators lurking behind them, but they have poor depth perception, making it hard for them to see windows until it’s too late.
But not all birds die after a crash. Some fly away. What happens to those birds? The truth is, scientists have no idea.
“A lot of the monitoring programs are based on finding dead birds or birds that are severely injured,” says Lucas DeGroote, avian research coordinator at Powdermill Nature Reserve, Carnegie Museum of Natural History’s biological field station in the Laurel Highlands. “We could be underestimating how big this problem really is.”
But not for long if DeGroote has anything to say about it. He’s been collecting data for three years using an emerging technology known as Motus.
Latin for “movement,” Motus consists of two relatively simple parts: tiny, lightweight transmitters that can be attached to birds as small as a magnolia warbler, which weighs about as much as two pieces of paper; and receiving stations, radios that can pick up the signal from a transmitter up to nine miles away. The genius of Motus is that each transmitter produces a ping that is unique, which means a bird wearing one of these tags is under surveillance everywhere it goes for the life of the bird or the battery—whichever dies first.
This is an enormous upgrade to the bird-banding system that avian scientists have used since the early 1800s. Banding continues to be invaluable for long-term scientific studies. But bird bands have their limits, since they only tell us something when a bird is caught by another researcher or found dead by someone who knows to submit the data online.
Bands only tell us about the bird in hand, so to speak. Motus can tell us about the bird in the bush.
As part of a national U.S. Fish and Wildlife Service-funded research initiative, DeGroote and his team are partnering with scientists, wildlife rehabilitators, and volunteers in Pittsburgh, Cleveland, and Baltimore to attach transmitters to six species of birds that have hit windows and undergone rehabilitation and release. At the same time, bird-banding operations near each city have been attaching transmitters to birds of the same species that have not struck glass. Then, as both groups are released, the Motus network provides real-time data on where the birds end up.
While it’s early in the process, the project is already producing some interesting results.
Sometimes the glass-smacked birds turn up dead a stone’s throw from where they were released. Sometimes they migrate in unexpected ways. DeGroote says one of the gray catbirds they tagged after a collision in Cleveland flew due east all the way to Boston. When it hit the sea in mid-June, it turned south toward Cape Cod. Then it disappeared. This is really unusual because the bird should have been breeding in June, not heading south. On the other hand, two magnolia warblers, one that hit a window in Cleveland and one that was captured at a banding station in Presque Isle, both migrated 350 miles northeast to the mouth of the St. Lawrence River in less than five days.
Of course, the flights of a few birds aren’t enough to draw conclusions. But DeGroote says around half a dozen other gray catbirds that had hit windows and were released likely didn’t survive long enough to migrate at all. This suggests that some species may be more affected by collisions than others.
Jasinski says people often tell him that they saw a bird hit a window and fly away fine.
“Well, is it really fine?” he wonders. “This study, that’s where these questions are going to be answered in the next few years. We’re going to see what is really happening.”
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