For songbirds, migration is the most difficult time of year. As they pass through thousands of miles of varied terrain, migrants must navigate a host of threats while urgently searching for habitat where they can rest and refuel. For a long time, it was assumed that birds completed these daunting journeys alone. But new research suggests migration is no solitary trek—it’s a social affair that encourages different species to band together. In a pioneering study published last week in the Proceedings of the National Academy of Sciences, researchers discovered that songbirds socialize across species lines, forming “migrating communities” as they travel. While ornithologists previously believed migrant species like the American Redstart and Magnolia Warbler just happened to end up flying near one another, we now know that this closeness is no coincidence: It’s a sign that different bird species can form ecologically meaningful relationships and may even help each other out...