Leo Uesaka strapped cameras onto seabirds to study their takeoffs. What he got instead was a barrage of poop footage.
“I was surprised to see how frequently the birds defecated in the video footage,” Uesaka told Science News. The University of Tokyo biologist had accidentally uncovered one of nature’s least glamorous but nevertheless revealing behaviors: streaked shearwaters poop a lot, and they almost exclusively do it midair above the ocean.
Clockwork Excretion
From 2021 to 2023, Uesaka and colleague Katsufumi Sato followed streaked shearwaters (Calonectris leucomelas) nesting on Funakoshi Ohshima Island in Japan. Tiny belly-mounted cameras recorded nearly 36 hours of foraging trips. In that time, the birds dropped 195 loads. Just one occurred while a bird was floating. Everything else splattered into the Pacific from above.
The researchers found that each bird pooped every 4–10 minutes. That works out to more than five times an hour, losing around 5 percent of their body mass in droppings each hour. Some birds even took off from the water just to relieve themselves, landing moments later.
To balance the books, the birds are constantly feeding, foraging while flying. Shearwaters skim vast stretches of the Pacific, snatching squid, fish, and other prey directly from the water surface.
Why such clockwork regularity? The paper describes it as a “precise periodicity” maintained within a margin of a few minutes. Whether this is a digestive quirk or an evolved strategy isn’t yet clear. But the payoff may be aerodynamic: flying with a lighter load is easier. As one outside researcher put it, “When the load is too heavy, you have to leave it behind, right?”
Hygiene, Predators, and Pathogens
Pooping in flight may also keep the birds clean. Their waste carries pathogens like avian influenza. Excreting on the wing means less chance of wading in infected muck. It might even help to avoid predators. Sharks and seals can track smells in the water, and a plume of guano could act like a glowing arrow pointing to dinner.
Still, not every bird benefits equally. Uesaka noticed that while some shearwaters rested on the surface, others circled above, dropping feces that rained down on their companions. That behavior could accelerate the spread of viruses such as bird flu between flocks. “Understanding the frequency of defecation at sea is key,” he said.
As odd as this may sound, it matters for the ocean, too. Seabird guano is packed with nitrogen and phosphorus. Near land, those nutrients supercharge coral reefs and fish populations near nesting islands. In the open ocean, the cumulative effect of hundreds of millions of seabirds could rival the “whale pump” — the way whales fertilize surface waters by pooping after deep dives.
Biologist Joe Roman, who studies nutrient cycles, put it in broader terms during an interview with Scientific American: “Everything from the smallest insects to bison to wolves — all species can play a role in this movement of nutrients between systems.”
Shearwaters, so it seems, are aerial nutrient couriers. Every few minutes, they offload packages that ripple through marine food webs.
What began as a study of bird legs has become an unexpected window into the secret circulatory system of ecosystems. The ocean’s health depends not just on what animals eat, but on what they expel. And thanks to a few backward-facing cameras, scientists now know that some of the Pacific’s most elegant fliers are also some of its most relentless fertilizer machines.
“You’d be surprised that a paper on bird poop could be that fascinating,” Kyle Elliott, a behavioral ecologist at McGill University, told the New York Times.
The findings were published in the journal Current Biology.
