Changing weather is affecting songbirds’ migration. Tracking devices will find where they're going
In 2020, the world saw its fair share of extreme weather and natural disasters. At the end of that summer and into that fall, the western United States was enveloped in severe wildfires, and smoke plumes filled weather reports. Laramie and its surrounding areas had a severe wildfire that spread a blanket of smoke across the sky. A month later, there was a cold snap, and temperatures dropped into the single digits. Suddenly, thousands of reports of migratory dead bird sightings were posted on citizen science apps.
Di Yang is a geographer and geospatial scientist from the University of Wyoming (UW). She and a team of researchers hypothesized that the birds were trying to leave a month earlier than usual as a result of the cold snap, but they got caught by it.
“We use citizen science data and try to put that into the geospatial modeling to find the reasons and the drivers of what is really causing the massive bird death,” Yang said.
After she collected the data from citizen science apps like Inaturalist and Ebird, Yang said she found that the combination of the smoke and the cold snap made the largest contribution to migratory bird deaths.
Two extreme weather events following each other is pretty dramatic and has a big impact on songbirds. However, even smaller phenomena like the seasons ending and starting earlier are also having impacts on them.
Until recently, UW researchers didn’t have enough funding for the technology that would allow them to track small songbirds. Now, researchers are using a light geolocating device to track when and where small songbirds are migrating.
UW associate professor and researcher in the Zoology and Physiology department, Anna Chalfoun studies declining species in Wyoming. She said some variation in when birds arrive in Laramie in the spring is normal.
“Our [nesting] sites are fairly high elevation sites, so you get a lot of annual weather variation,” she said. “We’ll get several weeks of variation in terms of when the first main pulse of nesting begins.”
But she said rising temperatures can lead to what is called a temporal mismatch. That means birds may migrate to their breeding grounds earlier than when their food sources are present. For example, plants they depend on may have not budded or insects may not be reproducing yet.
This may have been the case in June 2021. Laramie experienced an abnormally hot summer where temperatures reached the high 80s and low 90s F. Chalfoun and UW Ph.D. student, Emily Shertzer, observed migratory birds that usually nest in Laramie until September were already gone in June. Shertzer said the birds may have migrated to a different location.
“It’s super hot, so there’s probably fewer insects, and [that makes it] harder to feed their young,” she said.
Unfortunately, Shertzer and Chalfoun can’t know for certain where they went because they had no way to track these small songbirds, like finches and sparrows.
The only evidence they had was that people found lots of dead songbirds on migratory routes. Shertzer said the deaths could be because they were caught in the extreme heat.
“There’s a good chance a lot of our birds were caught by that. But, unfortunately, because we don’t have GPS trackers, we can’t say for sure when they died. But, we do know it was a rough year,” Shertzer said.
Shertzer and Chalfoun pointed out that small songbird research gets less funding than game bird research. Also, game and large migratory birds can be tagged with a satellite transmitter. Sadly, Chalfoun said those transmitters are too heavy to put on small songbirds.
“There are a lot of songbird species that are very tiny,” she said. “I think 10 grams is just the weight of a few paperclips, so tiny, tiny birds. And so, this is as good as technology has gotten us.”
Chalfoun is referring to the light geolocator technology. The geolocator is small enough to attach to small birds without harming them or impacting their ability to fly. It was invented in 2007, but researchers at UW only began using them in late 2021. That’s because they weren’t able to get funding for the trackers until then.
Shertzer pulled out one of the trackers from a white envelope. It looks like a wire butterfly. The wire is cinched in shoelace fashion to a small bulb.
“We figured out the size that works for each species by testing them out for a little bit. And then, all the harnesses are the same size for each species,” Shertzer said.
They wrap the harness around a bird’s legs and the bulb stock will rest on its chest or abdomen. The bulb can’t tell researchers exactly where the bird is since it’s not a satellite transmitter, but the bulb tracks light throughout the day, so researchers can find approximate locations based on what time the sun is rising and setting, according to the tracker.
So far, they put the harness on 100 birds of different songbird species, including sagebrush sparrows and sage thrashers. Chalfoun said they want more data before they can suggest how and why these tiny songbirds are changing their migration. However, they are hopeful that the technology will allow them to get that data, so they can find out why songbird populations are declining.
“It’s a first attempt at starting to expand our understanding,” Chalfoun said.
Chalfoun and Shertzer said they hope that satellite transmitters will soon be small enough to attach to small birds. That way, they can upload data without having to recapture the birds and get more reliable data. Until then, the light geolocators are the best technology they have.