Imma Perfetto
Cosmos science journalist
A study of thousands of hours of flight calls suggests that songbirds may be forming social connections with other species as they migrate, possibly even exchanging information about the journey.
It’s time to rethink songbird migration through a social lens, says Benjamin Van Doren, assistant professor at the University of Illinois and lead author of the study published in Current Biology.
“This study really calls into question the long-held idea that songbirds migrate alone, solely following their own instincts,” Van Doren says.
Van Doren and collaborators used machine learning to process and analyse 18,300 hours of acoustic recordings of autumn nocturnal bird migrations from over 26 sites in eastern North America. They detected the signature flight calls of 27 species, including 25 well-sampled songbirds.
The team measured how often different species’ calls could be heard together in the same recording – testing 15, 30, and 60 second intervals – and found stronger associations between species than expected by chance alone.
These social associations were stronger among species with similar wing size and calls.
“Species with similar wing sizes were more likely to associate, and wing length is directly linked to flight speed,” Van Doren says. “If you imagine 2 species flying at similar speeds because they have similar wings, then it’s much easier for them to stick together.
“As for vocalisations, 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.”
Last year, the co-authors found that birds across northeastern North America “buddy up” with other species at stopover sites during migration. Their new findings suggest that social relationships between songbird species are also important during migratory flights.
“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,” says Van Doren.
They speculate that short-lived songbird species, which do not learn their migration routes from their parents, may rely on social ties with other species alongside innate patterning and memory to make the journey. As climate change and habitat loss causes declines in bird biodiversity, this may jeopardise co-migrating partner species in unknown ways.
“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,” says Van Doren.
To better understand these dynamics, the team now plans to attach tiny microphones to individual birds to track their “conversations” throughout migration.
