Migrating Birds Sing to Team Up with Other Species
NEWS | 28 March 2025
Tiny songbirds such as grosbeaks and warblers migrate thousands of miles, flying at night and resting during the day, to and from their wintering grounds—and unlike many larger birds, they often forgo flocks and travel independently. But recent research suggests they’re not entirely alone in the dark sky. Benjamin M. Van Doren, an ornithologist at the University of Illinois Urbana-Champaign, and his colleagues set up ground-based microphones at 26 sites across eastern North America and collected more than 18,300 hours of calls from birds in flight. The researchers found that solitary migrating songbirds seem to cooperate across species, possibly sharing information with other solo travelers about who they are and what to watch out for ahead. The findings, published in Current Biology, add to growing evidence that interspecies social interactions may influence songbirds’ migratory behavior far more than was previously believed. The conventional wisdom had been “that each bird is following its own internal instinct or its own experience,” Van Doren says. “If it is not a young bird and has already migrated a few times, they definitely rely on memory and experience—but generally they’re just on their own.” On supporting science journalism If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today. Flying in the dark presents challenges to airborne cooperation; for example, visual cues such as other birds’ flight paths are absent. And it presents challenges to researcher observations, too, notes biologist Allison Pierce, who studies plover migration at the University of Colorado Denver and was not involved with the new study. To examine the process, Van Doren and his colleagues had to look—or rather listen—for alternative data: the seemingly random pings songbirds chirp out every few seconds to every minute. “It’s really been unclear why exactly they are spending all this energy and all this effort calling while they’re migrating,” Van Doren says. “There must be some reason or benefit to this behavior. Otherwise they’re just wasting energy.” To analyze what ended up being a gigantic amount of data, Van Doren and his colleagues used machine-learning technology adapted from Merlin, a bird-call-identification app developed by the Cornell Lab of Ornithology. The scientists found that individual birds from different species were flying near one another and calling out using certain patterns, “more so than we could explain by chance,” Van Doren says. So there appeared to be some reason the birds were staying in proximity. Rather than the birds finding their way from Chicago to Argentina completely solo, he says, “maybe there’s actually some social information being exchanged among these billions of songbirds migrating at night, which would totally flip around our understanding of how songbird migration works.” It’s still unclear exactly what information the birds may be communicating, Van Doren says. But researchers have some pretty good guesses. For instance, different bird species had different calls, but even within the same species, their “pings” varied across age or sex groups—suggesting that birds might be using such information to introduce themselves. Whatever the case, it’s highly likely that “staying in touch with other individuals could help them navigate more effectively,” Van Doren explains. They could be exchanging knowledge about landing spots and tricky weather conditions such as fog or rain, for example. “Migration is a very risky time even for birds that have done it before.” Scientists have previously observed that songbirds form what appear to be mixed-species flocks while searching for food and avoiding predators during the day, Van Doren adds. The new study suggests such partnerships could play a more significant role than researchers realized. Ideally, additional studies will further test these hypotheses by using more direct methods such as tagging specific birds to track them during migration. According to Pierce, “if we could take it from this big population-level scale and try to understand what the individual’s doing, it is going to be a key to understanding how birds are migrating.” Van Doren adds, “To me, it speaks to the amazing complexity of how nature works—and it’s exciting to be still learning new things about these well-known phenomena that are just spectacular.”
Author: Sarah Lewin Frasier. Gayoung Lee.
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