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Seabirds poop a lot. Where they gather on land, their excrement forms piles of guano, a material so rich with nutrients that access to the fertilizer ignited wars in South America in the 1800s.

Recently scientists have found mounting evidence that guano is also highly valuable when it reaches the sea, nourishing marine life. But without a way to keep tabs on where and when seabirds relieve themselves, accurately estimating the impact of their droppings on open-ocean ecosystems has been impossible. Until now.

In in the journal Current Biology, researchers in Japan say they’ve learned that seabirds called Streaked Shearwaters are prodigious poopers whose waste likely sustains marine food chains, even in regions far from dry land. And they’ve got video to prove it.

Lead researcher Leo Uesaka had his mind on loftier things—the biomechanics of takeoff—when he began the project. “The study actually started off with a coincidence” says Uesaka, an ecologist at the University of Tokyo and the National Center for Scientific Research in France. To investigate how the birds took flight, Uesaka and his research team caught shearwaters nesting on Funakoshi Ohshima Island in northern Japan and strapped rear-facing cameras to their bellies. But Uesaka quickly discovered that the cameras were great at capturing something that scientists knew little about: birds pooping at sea.

So, he and co-author Katsufumi Sato pored over roughly 36 hours of footage from 15 Streaked Shearwaters to learn more. They found that the excretions occurred almost exclusively while the birds were in flight, with around half happening shortly after takeoff, which suggests the birds may dump the extra weight to help lighten their loads during flight, Uesaka says. Even though carrying less cargo would make it easier to take off from the water, which burns up a lot of energy, the shearwaters almost never defecated while floating on the open ocean. The birds may hold it in for good hygiene and to avoid attracting predators, the researchers say.

The scientists were surprised not only by the timing of the Streaked Shearwaters’ bowel movements, but also by their sheer volume. “After I collected the data and watched the videos, I found that they actually poop quite a lot more than I expected” says Uesaka. The seabirds defecated every 4 to 10 minutes, the recordings showed. By multiplying that frequency by the average size of droppings found on land, Uesaka figures that shearwaters are excreting more than 5 percent of their body mass per hour—roughly their entire mass in a day—though he emphasizes that it’s only an estimate.

While each individual dropping is minute, cumulatively they make a big splash. Uesaka estimates around 100,000 shearwaters nest on the island, part of a global population of albatrosses, petrels, and shearwaters. Together they produce a vast quantity of natural fertilizer that could fuel life in parts of the ocean low in nitrogen or phosphorus, says Casey Benkwitt, a marine ecologist at Lancaster University who was not involved in the study. “It starts at the bottom of the food web and boosts productivity and growth,” she says. In her own research, Benkwitt found that coral reefs bounced back faster from bleaching damage if they were located near guano-supplying seabird colonies. Being able to quantify and characterize poop patterns is an important step toward understanding the effects of guano on ocean health more broadly, she says.

While bird droppings can give ecosystems a boost, they may also pose a risk as a vector for avian flu. To date, the disease has killed hundreds of millions of wild birds and has spread to every continent except Oceania. Seabirds have been hit hard, but many of them are loyal to their breeding colonies, so scientists aren’t sure how the flu is spreading from one colony to another. “There are almost no studies on the infection route of avian flu when it comes to pelagic seabirds,” Uesaka says. Although he says the disease has not yet been detected in Streaked Shearwaters, the new study’s findings suggest that seabirds may be infected when they congregate and defecate on their open-ocean feeding grounds. Knowing where different bird species mingle could be key to understanding how the disease spreads, Uesaka says.

To find out, Uesaka says he hopes to attach GPS trackers to the birds along with the cameras. That way, he’ll know exactly where all that guano is being dropped. Researchers could also strap cameras to different species of seabirds to see if they produce similar quantities of waste. Watching videos of birds pooping might sound more like grade-school behavior than serious research, but it could be key in helping scientists flush out how seabirds contribute to ocean health—and how we can help keep them healthy, too.