There's a mystery afoot in the moss world.

Mosses, liverworts, and hornworts—collectively known as bryophytes—have some of the widest ranges of any species on the planet. Why genetically close populations can crop up thousands of miles apart, from the frigid tundra to the balmy Argentinian countryside, is a question that has baffled scientists for decades.

As it turns out, migratory birds may be their long-distance carriers.

Researchers at the University of Connecticut believe that migratory shorebirds carry diaspores—the seeds or spores plants use to reproduce—in their feathers, a possible mechanism for the plants' amazing ranges. While this theory was proposed by botanists as long ago as the 1940s, "it's all been circumstantial until now," said Lily Lewis, lead author on the paper.

In a study published this week in PeerJ, Lewis and her colleagues sampled feathers from eight shorebird species in the summer months before their annual migration from the Arctic to their wintering grounds below the equator in South America. They found that three species—the semipalmated sandpiper, the red phalarope, and the American golden plover—were carrying bryophyte diaspores on their bodies, likely thanks to their habit of nesting on the ground in mossy beds.

Though just 23 birds were screened, Lewis is optimistic they've uncovered a common phenomenon. "Certainly a greater sampling will improve our inferences," she said, "but even with that small sample size we still found a lot of diaspores."

Even if shorebirds did transport the mosses over long distances, would the plants survive the trip? Lewis and her team are already culturing them in the lab to find out. They expect they bryophytes will grow just fine: Another group of scientistsrecently discovered moss specimens buried beneath a glacier for 400 years. After all that time, they were still capable of growing.

Bryologists and ornithologists worked together to unravel the mystery in a symbiosis that mirrors their findings: The study is an example of the surprising connections between two very different organisms—and the amazing ways they work together in the natural world.

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