Streaked shearwaters poop only while flying over the ocean

This seabird poops on the fly.

Streaked shearwaters, oceanic birds that spend much of their time out on the open Pacific Ocean, defecate almost exclusively in the air, researchers report August 18 in Current Biology. Pooping in flight could allow these birds to avoid wading in their own feces, which can contain pathogens such as bird flu. The poop may also serve as ocean fertilizer.

Seabird guano provides nutrients to soil and water near coastal nesting sites. But how shearwater poop affects nutrient cycling at sea is unclear. While whales move nutrients vertically in seawater by feasting in deep water and defecating at the surface, seabirds may “have a stronger local effect in areas where they gather in large numbers,” says biologist Leo Uesaka.  

Uesaka and behavioral ecologist Katsufumi Sato, both of the University of Tokyo, had taped cameras to the bellies of streaked shearwaters (Calonectris leucomelas) to study how the birds take off from the water. These cameras, facing backwards to capture the birds’ legs as they ran, also picked up when they pooped. “I was surprised to see how frequently the birds defecated in the video footage,” Uesaka says. “Enough that it became its own line of investigation.”

During nearly 36 hours of recordings from 15 streaked shearwaters nesting on Funakoshi Ohshima Island off the coast of Japan, the team captured 195 poops. Just one happened while a bird was in the water. Uesaka suspects that was due to accidental gut pressure.

Defecating from the air may not only help the birds stay clean but might also reduce the risk of attracting predators to fecal plumes. In flight, these birds can poop every few minutes, losing roughly 30 grams of mass per hour, or about 5 percent of their body mass. Frequent pooping may help streaked shearwaters stay in the air with less effort, Uesaka says, because feeding can increase the energy needed to fly.

These findings could help researchers better understand how pathogens such as bird flu transmit among large groups of birds. While the virus can spread within colonies as birds nest on land, transmission among birds from different colonies is less clear. Because the virus is transmitted via droppings, Uesaka says, “understanding the frequency of defecation at sea is key.”