European starlings in flight at sunset. Arterra / Universal Images Group via Getty Images
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If you were a bird flying thousands of miles over land or sea with other migrating birds, what would you talk about to pass the time?
Songbirds may converse with other species during their long migrations, forming social bonds and possibly exchanging information about the flight, according to a new study led by researchers at University of Illinois Urbana-Champaign (UIUC).
“The night sky teems with migrating songbirds, aloft in their millions following routes etched in evolutionary time. But those flight paths may not be entirely innate,” a press release from UIUC said.
The researchers analyzed data from more than 18,300 hours of calls recorded in-flight, which suggested songbirds might “talk” with migration mates.
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“We can’t be sure what they’re saying, but birds might broadcast calls during flight to signal their species, age, and sex. And we can certainly speculate that these flight calls could relate to navigation or finding suitable stopover habitat,” said lead author of the study Benjamin Van Doren, an assistant professor in UIUC’s Department of Natural Resources and Environmental Sciences, in the press release.
Research from 2024 by co-authors of the new study at the University of Maryland Center for Environmental Science, Appalachian Laboratory found evidence to suggest that songbirds “buddy up” with other migrating species at stopover sites, but until now there wasn’t any evidence that different species “pair up or communicate vocally on the wing.”
Van Doren believes memory and innate patterning are important drivers of behaviors during migration, but said “it’s time to rethink songbird migration through a social lens.”
“In recent years, there has been an increasing recognition of the importance of social information in bird migration, but scientists have mainly documented this in species that travel during the day or in family groups,” Van Doren noted. “The social environment also seems to be important in species like hawks and storks that form huge aggregations during their daytime migrations. Young birds learn behaviors from observing other birds and how they navigate — and not necessarily from family.”
Most songbirds make their journeys at night, when visual cues aren’t necessarily discernable. This led Van Doren to think about the possibility of other social cues, so he used his access to acoustic recordings from 26 sites of autumn nocturnal bird migrations in eastern North America taken over a three–year period.
“These nocturnal acoustic recordings are really the only window onto this unseen but absolutely massive flow of birds — hundreds of millions aloft over the U.S. on any given night during migration,” Van Doren said. “It’s something people aren’t usually aware of because it happens when we’re sleeping.”
Songbirds migrating at night. TOLGA DOGAN / iStock / Getty Images Plus
The thousands of hours of recordings were processed by a machine learning tool that allowed the research team to detect 27 species’ signature flight calls, including 25 well-sampled songbirds.
The team first identified species, then measured the frequency with which certain calls co-occurred, testing at intervals of 15 seconds, half a minute and one minute. They found associations that were stronger than would be expected by chance, regardless of the time elapsed.
Searching for an explanation of the associations, the researchers found that the similarity of calls and wing lengths of species were most important. By contrast, birds who “buddy up” during migration stopovers were not maintaining the same relationships while flying, nor were they necessarily in the air with closely related birds or species who shared their specific habitat preferences.
“Species with similar wing sizes were more likely to associate, and wing length is directly linked to flight speed. If you imagine two species flying at similar speeds because they have similar wings, then it’s much easier for them to stick together,” Van Doren explained. “As for vocalizations, it is possible that species’ calls have converged over time because of this social link or that species that happen to give similar calls are simply more likely to gravitate towards each other.”
Van Doren noted that 25 individuals was a small representative subset of songbird species who migrate at night, some of whom don’t vocalize during flight. Van Doren and his team have plans to conduct more research, including tracking individual birds’ “conversations” with flight partners by attaching tiny microphones to be worn throughout their migrations.
The preliminary results bring up many speculative theories, such as that short-lived songbird species who aren’t able to rely on their parents for guidance might rely on social ties during the journey. In addition, the rapid loss of bird biodiversity due to habitat destruction and climate change may jeopardize co-migrating partner species.
“This study really calls into question the long-held idea that songbirds migrate alone, solely following their own instincts,” Van Doren said. “Learning more about the consequences of these social connections — not only for migration, but also for other aspects of their biology — will be important to inform and manage the risks they face in a changing world.”
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