Evidence collected from over 18,300 hours of recorded flight calls suggests that migrating songbirds may communicate with different species, building social relationships and possibly sharing knowledge about their migrations.
The night sky is alive with songbirds on the move, millions pursuing paths crafted by evolution. However, new research from the University of Illinois Urbana-Champaign indicates that these migration paths might not be purely instinctual. Analysis of more than 18,300 hours of flight call recordings reveals that songbirds may “talk” to other species as they migrate, forming social links and potentially exchanging valuable information regarding their travels.
“Although we can’t definitively decipher their calls, it seems likely that birds use their vocalizations while flying to communicate aspects like species, age, and gender. We can also speculate that these calls may help with navigation or finding appropriate resting places,” stated Benjamin Van Doren, the study’s lead researcher and an assistant professor in the Department of Natural Resources and Environmental Sciences at Illinois. This research began during his time at the Cornell Lab of Ornithology.
Prior studies conducted by co-authors from the University of Maryland Center for Environmental Science, Appalachian Laboratory showed that birds often associate with other species at migratory stopover sites. However, up to this point, there was no proof that different songbird species interacted vocally while in flight. Although Van Doren recognizes that innate behavior and memory are vital for migration, he argues that it may be time to examine songbird migration through a social lens.
“In recent times, there’s been an increasing recognition of the role of social information in bird migration, primarily observed in species that migrate during the day or in family groups,” he noted. “The social context also seems important for species like hawks and storks, which gather in significant numbers during their daytime migrations. Young birds often learn from the behaviors and navigation skills of other birds, beyond just those in their immediate family.”
However, when flying at night, visual communication is unavailable, leading Van Doren to investigate other means of social interaction. Fortunately, he had access to a vast archive of acoustic recordings from autumn bird migrations, collected from 26 locations over three years in eastern North America.
“These nocturnal recordings afford a rare glimpse into this largely unseen but extensive movement of birds – hundreds of millions flying across the U.S. each night during migration,” Van Doren noted. “This event often goes unnoticed by many since it takes place while they are asleep.”
Before the advent of advanced AI methods, processing and analyzing the 18,300 hours of acoustic data would have been an overwhelming task. Now, with the help of a machine learning tool, Van Doren’s team swiftly identified the flight call patterns of 27 species, including 25 commonly observed songbirds.
After identifying these species, the researchers analyzed how often specific calls occurred together in different time intervals of 15, 30, and 60 seconds. They found that the associations between species were stronger than what would be expected by chance, no matter the time frame.
To explore these interactions further, they discovered that the species’ wing lengths and the similarities in their calls were the most significant factors contributing to these connections. Interestingly, birds that flock together during stopovers did not necessarily maintain these associations while in flight, nor did they always migrate alongside closely-related species or those with specific habitat needs.
“Species with comparable wing lengths tended to stick together because wing size affects flight speed. If two species have similar wing structures and fly at similar speeds, they can more easily remain together,” Van Doren explained. “As for vocalizations, it’s possible that the calls of these species have evolved to resemble one another over time due to social interactions, or perhaps species with similar calls are more likely to come together.”
Van Doren acknowledges that the 25 species studied represent just a small portion of the nocturnal migrating songbirds, many of which do not produce sounds during flight. He and his team aim to continue their research by attaching small microphones to individual birds to monitor their “conversations” with flight partners throughout their migrations.
Although preliminary, these findings prompt numerous intriguing and speculative ideas. For instance, short-lived songbird species that lack parental assistance might rely on social bonds with others to navigate their journeys. Furthermore, the significant decline in bird diversity caused by climate change and habitat loss could jeopardize the relationships between migratory partner species.
“This research challenges the long-held belief that songbirds migrate alone, following only their instincts,” Van Doren stated. “Understanding the significance of these social connections not only regarding migration but also in relation to their overall biology is essential for addressing and managing the dangers they face in a changing world.”
