Slimy mud is magical for an animal
In the spring in the Georgia Strait in Canada, when the tide comes every day, the mudflats south of Roberts Bay become an open-air restaurant for the West Sandpiper. The western sandpiper is a small wading bird (generally refers to a long-legged bird that wades on the shore of a body of water) and has a strong migratory ability. Every year, hundreds of thousands of sandpipers migrate from Panama to Alaska to breed, and Roberts Bay is their last stop before reaching their Alaska breeding grounds. In order to maintain enough strength to complete the journey north, the West Sandpiper needs to rest and eat in Roberts Bay. Strangely, in addition to running back and forth, these birds spend most of their time sucking slimy mud on the ground along mudflats, just as marathon runners suck energy gels to replenish their strength.
The mud was also delicious
Scientists once thought that mud-sucking sandpipers were trying to find invertebrates such as aquatic insects, crustaceans, and molluscs. But later, they discovered that the sandpipers were frantically sucking a snot-like film on the surface of the mud — a biofilm composed of photosynthetic bacteria, algae and other microorganisms and their secretions.
So, how do these biofilms form? Why do sandpipers feed on them? It turns out that some "witty" photosynthetic bacteria, algae and other microorganisms secrete mucus to attach themselves to the surface of the mud, so that they can temporarily settle down and not be swept away by the sea. Don't look at these biofilms like slimy snot, for the sandpiper, they are a nutritious delicacy. Although sandpipers inevitably eat some sediment when they suck on biofilms on the surface of mud, these biofilms are easier to locate and prey on by sandpipers than invertebrates, saving them a lot of physical strength.
A snipe is feeding on biofilm
So how does the Westshore Sandpiper scrape these biofilms? Scientists observed under a microscope that the outer edge of the sandpiper's tongue was covered with many tiny "burrs." These "burrs" make the sandpiper's tongue look like an old coarse carpet, or like a toothbrush head that has been used for too long. It is with the help of these "burrs" on the outer edge of its tongue that the sandpiper scrapes the biofilm. Scientists looked at six intertidal zones (the average high and lowest tide coasts) in Japan and Canada, and after studying 30 different plover birds, found that not only western sandpipers, but almost all small water birds use their beaks and furry tongues to suck biofilms, and the "burrs" on the tongues of these smaller birds are more developed. Because the digestive organs are too small, smaller birds have difficulty digesting large or hard food, and in addition, their beaks are usually shorter, so they cannot prey in deep sediments. Scientists theorize that these smaller birds evolved their tongue morphology and foraging behavior in order to prey on smaller, softer foods, such as biofilms.
The tongue of a western sandpiper as seen under a microscope
Not all mudflats will be patronized
The biofilm on the surface of the mud is not only nutritious, but also provides the western sandpiper with the energy to continue its northward migration. This is because, under the right conditions, these biofilms photosynthesize and produce sugars and fatty acids. Studies have shown that the energy provided by the biofilm can meet up to 68% of the energy needs of the sandpiper during migration.
Curiously, in the mudflats tens of square kilometers south of Roberts Bay, westshore sandpipers mainly congregate in the supratidal zone just 300 meters from the coast. After classifying the stomach contents of the sandpiper and recording its foraging behavior, scientists found that this area turned out to be the place where the biofilm was thickest, most nutritious and exposed for the longest time. Because the area is at the mouth of the Fraser River, fresh water mixes with seawater to create just the right salinity for halophytic algae, prompting them to produce large amounts of fatty acids. Polyunsaturated fatty acids play an important role in the health of organisms, so sandpipers need to supplement this substance with food. As a result, the sandpiper became picky and picked on the "abundant" biofilm on the mudflats. For example, biofilms in some bays contain a higher proportion of polyunsaturated fatty acids, and sandpipers that stay here will suck more biofilms; In some bays, the proportion of fatty acids with lower nutritional value in biofilms is larger, and at this time, the sandpiper does not look at these snot-like substances on the mudflats, but spends more time hunting polychaete worms (which contain polyunsaturated fatty acids).
The western sandpiper is one of the most abundant plover birds in the world. Scientists speculate that the alarming number of sandpipers may be related to their consumption of biofilms, a nutrient-rich food resource. Without these slimy biofilms, most sandpipers would not be able to complete their long-distance migrations. In this way, the biofilm in these slurries can be said to make a huge contribution