Streaked shearwater flying over the ocean. (© BirdMoreBo - stock.adobe.com)
In A Nutshell
- Streaked shearwaters almost always excrete in flight, with only one case observed on the water.
- Birds excreted every 4–10 minutes during daylight, often within seconds of takeoff.
- Researchers estimate streaked shearwaters may shed ~5% of body weight per hour, though this figure needs further validation.
- Findings suggest seabird excretion could influence nutrient cycling and disease transmission in the open ocean, but more research is required.
TOKYO — Scientists studying streaked shearwaters, seabirds that spend much of their lives gliding above the Pacific, have uncovered a surprising habit. These birds almost never relieve themselves while resting on the sea surface. Instead, they excrete almost entirely in flight, and at a rate that may amount to roughly 5% of their body weight per hour.
That figure is an estimate based on video data and measurements collected on land, and researchers caution it needs further testing. But if accurate, it suggests these long-distance flyers may be contributing far more to nutrient cycles in the open ocean than previously recognized.
Why Seabirds Only Poop While Flying
Researchers from the University of Tokyo and France’s Centre d’Études Biologiques de Chizé fitted 15 streaked shearwaters with small belly-mounted cameras at Japan’s Funakoshi Ohshima Island. Over 35.9 hours of footage, they recorded 195 excretion events.
Out of all these, only one occurred while a bird was floating on the water. The rest were airborne, sometimes even after the bird took off briefly just to excrete and then landed again.
“Considering the significant energy required for take-off from water, especially for Procellariiformes, this behavior implies that the benefits of excretion in flight outweigh the take-off costs,” the researchers noted in their paper, published in Current Biology.
Of 82 first excretion events during flight, half happened within 30 seconds of takeoff, and more than a third occurred within just 10 seconds.
Birds Follow Bathroom Schedules With Clockwork Precision
The birds’ timing was strikingly regular: most excreted every 4 to 10 minutes during daylight hours, maintaining a rhythm within a few minutes either way. Occasionally, they even made “excretion-only flights,” lifting off, defecating, and returning to the water within a minute.
Why avoid the water? The researchers suggest three possible reasons: excreting in flight helps birds avoid contact with their own feces and protects sensitive tissue from seawater; it may reduce the chance of attracting predators like sharks or seals; and the floating posture might simply not work well for the act itself.
How Much Bird Waste Actually Hits the Ocean
From their calculations, the team estimated that streaked shearwaters excrete about 30 grams per hour, or more than 5% of their typical 400- to 600-gram body weight. This is far higher than past estimates based on observations at land-based colonies. The authors note this value needs further validation, but it points to a potentially overlooked factor in seabird ecology.
For individual birds, such steady weight loss could influence flight energetics. Even small changes in body mass can affect the cost of flight for long-distance gliders. Whether this is just a byproduct of digestion or offers some flight advantage remains uncertain.
Scaled up, the implications grow. Roughly 424 million Procellariiformes (the group including shearwaters, petrels, and albatrosses) breed worldwide. While the full impact of their combined waste is still an open question, the researchers suggest it is an important subject of study, with some parallels to nutrient processes like the “whale pump.”
What This Means for Ocean Health and Disease
The study also raises questions about disease spread at sea. Seabird feces can carry avian influenza, but infection patterns among ocean-going species remain poorly understood. Frequent excretion during large feeding gatherings could create opportunities for transmission between birds from distant colonies.
“Seabird feces are a notable vector for avian influenza; however, infection dynamics in pelagic species remain poorly understood compared to those in shorebirds and waterfowl,” the researchers wrote.
Future research will need to test whether similar excretion patterns occur across other seabird species, seasons, and regions, and to measure their actual chemical impact on nutrient cycles. For now, the findings point to a new frontier: seabird behavior in the open ocean may play a hidden role in shaping ecosystems far beyond their nesting sites.
Paper Summary
Methodology
Researchers attached small video cameras to the bellies of 15 streaked shearwaters breeding at Funakoshi Ohshima Island in Japan between 2021 and 2023. The cameras faced backward to capture excretion events during the birds’ foraging trips at sea. Scientists analyzed 35.9 hours of video footage and recorded 195 excretion events, noting the timing, frequency, and behavioral context of each event. They also measured fecal mass on land to estimate total waste production rates.
Results
All excretion events occurred during flight except for one instance while floating on water. Birds showed precise timing, excreting every 4-10 minutes during daylight hours, with 50% of first flight excretions occurring within 30 seconds of takeoff. Researchers calculated that streaked shearwaters excrete approximately 30 grams per hour, representing more than 5% of their typical body weight. Many birds performed “excretion-only flights,” taking off solely to defecate before returning to the water.
Limitations
The study focused on a single seabird species during breeding season at one location, limiting generalizability to other species or seasons. Fecal mass measurements were taken on land rather than at sea, which may not accurately reflect open-ocean excretion volumes. The research doesn’t address the actual nutrient impact on marine ecosystems or verify the proposed explanations for flight-only excretion behavior.
Funding and Disclosures
The research was supported by Grants-in-Aid for Scientific Research from JSPS, Japan Science and Technology Agency SPRING, and the Cooperative Program of Atmosphere and Ocean Research Institute at the University of Tokyo. The authors declared no conflicts of interest.
Publication Information
“Periodic excretion patterns of seabirds in flight” by Leo Uesaka and Katsufumi Sato was published in Current Biology in 2025. The study was received in February 2025, revised in June 2025, and accepted in June 2025.
