The shimmering slime that fuels some of Earth's longest flights
In short: Migratory birds are marathon athletes, requiring massive amounts of energy to cross continents. To refuel, they don't just look for seeds or insects; they seek out a specific, nutrient-dense goo coating the mudflats. This microbial biofilm is a biological powerhouse essential for survival.
For long-distance migratory birds like the Western Sandpiper (Calidris mauri), stopover sites are critical refueling stations. These birds often fly hundreds or thousands of kilometers without rest, arriving at mudflats to recover from one leg of their journey and build fat reserves for the next. Their primary food source involves a thin, greenish biofilm, measuring just several millimetres, which covers the top of pungent deep-sea mudflats. The Western Sandpiper is a notable example of this behavior. These birds are often seen in large flocks at these sites. They specifically target areas where sunlight reflects off the surface.
While the mud may appear devoid of life to the human eye, these biofilms are produced by microbes and represent some of the most biologically productive ecosystems on Earth. The birds use bristly tongues to slurp up this 'goo,' which provides the high-calorie sustenance necessary for their grueling treks. Because migratory species often rely on a relatively small number of specific mudflats globally, the health of these tiny microbial layers is disproportionately important. These ecosystems also host various fish and invertebrates throughout the year. The mudflats serve as a primary source of energy for many different species.
However, these vital stopovers are under significant threat from human activity. Across the Yellow Sea, situated between China and North and South Korea, these mudflats have diminished by over 65 percent during recent years. Should this downward trend persist, three species that migrate could become endangered as early as 2026. Even indirect threats, such as proposed offshore container terminals in Canada's Roberts Bank, risk altering water salinity and upsetting the delicate balance of ecosystems that support over a million birds during peak migration months. Situated within British Columbia, the Fraser River Delta's southern tip hosts the Roberts Bank site. This specific area provides food for birds during three weeks in April and May.
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Sources
- Summary by Intellect · source: These Migrating Birds Fuel Up by Eating…Mud?
- Also: Slimy Mudflat Biofilms Feed Migratory Birds--and Could Be Threatened
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