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Songbirds socialize on the wing
during migration, new study says
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 [January 17, 2025]
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, according
to new research led by the University of Illinois Urbana-Champaign.
Evidence from over 18,300 hours of recorded flight calls suggests
songbirds may “talk” to other species as they migrate, forming
social connections and — just maybe — exchanging information about
the journey.
“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 study
author Benjamin Van Doren, assistant professor in the Department of
Natural Resources and Environmental Sciences, part of the College of
Agricultural, Consumer and Environmental Sciences at Illinois. Van
Doren began this research at the Cornell Lab of Ornithology.
Work from last year by the study’s co-authors at the University of
Maryland Center for Environmental Science, Appalachian Laboratory
suggested birds “buddy up” with other species at stopover sites
during migration, but there was no evidence until now that different
songbird species pair up or communicate vocally on the wing.
Although Van Doren believes innate patterning and memory are still
important drivers of migration behaviors, he says 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,” he said. “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.”
But those visual cues go dark at night, when most songbirds travel.
That’s what led Van Doren to wonder about other social cues.
Fortunately, he had access to acoustic recordings of autumn
nocturnal bird migrations from 26 sites over three years in eastern
North America.
“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.”
The 18,300-hour acoustic record would have been a processing and
analytical nightmare before AI. Now, a machine learning tool allowed
Van Doren’s team to quickly detect the signature flight calls of 27
species, including 25 well-sampled songbirds.
After identifying species, the team measured how
often certain calls co-occurred in time, testing intervals of 15,
30, and 60 seconds. Regardless of the time interval, they found
stronger associations between species than expected by chance alone.
Looking to explain these associations, they found
species’ wing lengths and the similarity of their calls were the
most important factors. In contrast, birds that “buddy up” during
stopovers weren’t maintaining those relationships in the air, and
they weren’t necessarily flying with closely related species or
birds that shared their preferences for specific habitats.
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American Redstart. Photo courtesy of Andrew Dreelin.
“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 said. “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 notes that 25 is a small subset of the songbird
species migrating at night, some of which don’t vocalize at all
during flight. He and his team plan to follow up with more
research, including attaching tiny microphones to individual
birds and tracking their “conversations” with flight partners
throughout their migrations.
Still, these preliminary results raise many intriguing, if
speculative, notions. For example, short-lived songbird species
who can’t rely on their parents to show them the way may instead
rely on social ties with others to make the trek. Also, the
precipitous loss of bird biodiversity with climate change and
habitat loss may jeopardize partner species that co-migrate.
“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.”
The study, “Social associations across species during nocturnal
bird migration,” is published in Current Biology [DOI:
10.1016/j.cub.2024.12.033] and represents a collaboration
between the University of Illinois Urbana-Champaign, the Cornell
Lab of Ornithology, the University of Maryland Center for
Environmental Science, Appalachian Laboratory, the University of
Leeds, Durham University, and Actions@EBMF. The research was
supported by an Amazon Cloud Credits for Research grant, the
Cornell Lab of Ornithology, the Cornell Presidential
Postdoctoral Fellowship, and the National Science Foundation
[award no. 2146052]. Additional funding was provided by NERC
(NE/V013483/1) and WildAI (C-2023-00057).
[Source:
Benjamin Van Doren, vandoren@illinois.edu
News writer:
Lauren Quinn, 217-300-2435,
ldquinn@illinois.edu]
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