Birds Form Surprising Relationships With Other Avian Species During Migration, Study Suggests

In the spring and fall, migratory birds make death-defying trips between distant sites, sometimes traveling from Canada all the way down to Mexico or South America. During their long treks, they may encounter bad weather and predators or contend with habitat loss and light pollution. Now, a new study suggests birds do not make these journeys alone—and they may actually be teaming up with other species during migration.

Scientists generally thought that birds of different species merely happened to fly near each other while migrating, without interacting much. But the research, published in Proceedings of the National Academy of Sciences in August, suggests this sharing of space isn’t by chance. Instead, the creatures form cross-species migrating communities that could prove to be beneficial to the birds.

“It seems like common sense: When all of these birds are concentrating in really high densities, they are likely interacting with each other,” says Joely DeSimone, the study’s lead author and a biologist at the University of Maryland Center for Environmental Science, to Audubon magazine’s Benjamin Hack.

Tracing the interactions between migrating animals can be difficult, but DeSimone and her co-authors approached the task by focusing on stopover sites—locations where birds rest and refuel during their migratory journeys. These sites also often serve as bird banding stations, where researchers capture birds in lightweight mist nets, study them and affix tiny numbered bands to their legs before releasing them back into the wild.

DeSimone and her team analyzed more than half a million records collected over 20 years to parse avian social networks. The data, collected from five different bird banding stations in northeastern North America, represented 50 songbird species.

“We found support for communities on the move—considering migrating birds as part of interacting communities rather than random gatherings of independently migrating species,” says study co-author Emily Cohen, a biologist at the University of Maryland Center for Environmental Science, in a statement. “This work could change the way we study and conserve animal migrations.”

In the study, the researchers focused on noting which species were present together and which species didn’t overlap at a stopover site. They ran an analysis to test whether various species appeared together more frequently than they would if their overlap was just random. But they didn’t record specific interactions between the birds.

“With our data set, we can’t say whether these relationships are positive or negative,” DeSimone tells National Geographic’s Jason Bittel. “We could be seeing affiliations among birds that are chasing each other into the net, or we could be observing aggressive relationships.”

But surprisingly, the researchers found that songbirds tended to show up together rather than avoid each other. American redstarts and magnolia warblers reliably appeared together in the researchers’ nets in spring and fall. The same thing happened with ruby-crowned kinglets and white-throated sparrows. Out of all the species, only American redstarts and ruby-crowned kinglets seemingly avoided each other—a pattern seen at just one banding site—but the researchers don’t know why.

The species that overlapped tended to have similar foraging habits and non-breeding ranges. Scientists had expected to see more competition, especially where food was concerned. But the prevalence of these overlapping encounters hints at a more positive network between them. “The presence of other birds with similar foraging behavior or similar food preferences may signal to newcomers where the good habitat is,” helping them refuel more quickly, DeSimone tells National Geographic.

Future research could examine whether successful migrations depend on these networks, or whether key links between species are vulnerable to habitat or climate changes, Steve Dudgeon, a program director at the National Science Foundation, which funded the study, says in the statement.

But for now, the paper is already pioneering a shift in understanding bird migrations.

“This really allows for a big picture view of what’s happening,” Janet Ng, a wildlife biologist at the department of Environment and Climate Change in Canada who was not involved in the study, says to National Geographic.

As humans build roads and cut down forests, migration becomes an increasingly difficult journey for many animals. For birds specifically, research has shown that sometimes their migratory behavior is rooted in their genes, and this could make it harder for them to rapidly adapt to new environmental conditions. But by changing the lens used to understand these bird species, the paper could help conservationists home in on where to direct their efforts.

“For a long time, scientists have been working under the idea that a lot of these birds just sort of do their own thing during migration,” says Jill Deppe, the senior director of the National Audubon Society’s Migratory Bird Initiative who wasn’t involved in the study, to Audubon. “Because we weren’t sure about whether birds were moving together and had these interactions, a lot of our approach to conservation has been one species at a time.”

But the findings suggest researchers should be able to help declining populations and fast-track conservation actions by understanding migration as communal, she adds. “One species at a time just isn’t going to be fast enough to protect these species and bend that bird curve.”

Alexa Robles-Gil | | READ MORE

Alexa Robles-Gil is a bilingual science journalist based in New York City. Her work has appeared in the Guardian, Undark, Inside Climate News and more.