Streaked shearwaters are large birds that search for fish over the western Pacific. Dr. Uesaka and his colleagues study the birds at their breeding ground on a small, uninhabited Japanese island.
A behavioral ecologist at the University of Tokyo, Dr. Uesaka had intended to study how the seabirds run along the water’s surface as they take off in flight. But when the No. 1 thing he noticed in his recordings was No. 2, he decided to shift his focus. He learned that streaked shearwaters almost never defecate in the water. Yet they go more than five times an hour, on average, while flying. The finding was published Monday in the journal Current Biology.
Scientists who attach video cameras to animals are usually seeking a creature’s-eye view. When Leo Uesaka stuck tiny cameras to the bellies of seabirds called streaked shearwaters, he turned those cameras around. So maybe what he captured wasn’t surprising — but the amount of it was.
“The frequency of the excretion is far more than I expected,” Dr. Uesaka said.
Curiously, though, the birds almost never did their business while resting on the water. The authors speculated that the birds might be trying to keep their back ends clean or avoid tipping off predators. Or maybe pushing out guano while floating is less comfortable for them.
Dr. Elliott said that it made sense for these birds to spend as little time on the water as they can. Like their relatives the albatrosses, shearwaters are efficient, wind-propelled fliers. Energetically, “It actually costs them less to fly than to rest on the water. So they really want to be flying,” he said. Sitting on the water might also make them lose body heat. For the streaked shearwaters, apparently, even a bathroom break isn’t worth a pit stop.
As meals from several hours ago travel through the birds’ digestive systems, Dr. Elliott said, the birds may simply be excreting as often as they’re able, to make their flight easier.
Seabird guano contains nitrogen and phosphorous that act as fertilizer wherever they fall. For example, coral grows twice as fast around islands with seabird populations than around neighboring islands with few seabirds. Populations of reef fishes are also greater around the seabird islands.
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