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Go to Brilliant.org/SciShow to learn how you can take your STEM skills to the next level! [♪ INTRO] Western sandpipers are small shorebirds that make an intense long-distance migration. Every year, hundreds of thousands of these birds travel from as far south as Panama up to their breeding grounds in Alaska.

For a little sandpiper to have the energy to travel marathon distances, it needs to stay fueled up along the way, which includes making stops for food. But these birds don’t just snack on bugs or worms: They also slurp up the mud along the shoreline as they journey north, like marathon runners slurping energy gel along their route. Now, western sandpipers aren’t licking the mud because it’s a tasty treat, although they do end up eating their fair share of the stuff in the process.

These birds are slurping a film off the /top/ of the mud. And that film is alive. This biofilm is made up of microscopic algal cells that grow together in a layer of mucus on top of the mud.

And at certain times of the year, which happen to coincide with the birds’ annual migration north, the conditions are right to trigger a massive algal bloom on the surface of the mud that’s just ripe for the … licking. In fact, these birds slurp this biofilm so regularly that they have evolved bristly tongues that make slurping the film off the mud easier. But it’s not actually the sugars that the algae produce while they’re photosynthesizing that are fueling the birds for their long journey.

Researchers working in Canada believe that fatty acids like omega 3s produced by the algae are responsible for the birds’ success. Algae don’t produce fatty acids all the time, just when they’re hanging out in conditions that make them a little stressed. At one important stopover site for the birds, along the Fraser River delta in British Columbia, the river discharges a large amount of fresh water into the bay after the spring snowmelt.

This large freshwater pulse is just enough to stress these salt-dwelling algae out, triggering them to produce fatty acids instead of sugars, right around when the birds are migrating. Fatty acids are a fantastic, long-lasting energy source. There are more calories per gram in fat than in carbohydrates or protein.

Researchers believe that these fatty acids are what’s ultimately fueling the birds, priming them for a successful journey north. And western sandpipers aren’t the only birds that do this! Researchers have found that their East Coast cousins, semipalmated sandpipers, behave similarly on their lengthy migrations as well.

There’s still work to be done to determine whether western sandpipers are fully dependent on the biofilm’s fatty acids to fuel their marathon migrations, or if it’s just an added bonus to all the other yummy things that they’re slurping out of the mud. Researchers are eager to find out for sure because some of the western sandpiper’s stopover sites are threatened by changes to their environment, like increasing developments along the shoreline. If they can prove that fatty acids are a vital source of energy for shorebirds, then conservationists can fight to protect shorelines and shorebird populations around the globe.

We learned all of that just from asking the question “Why are these birds licking mud?” If you are always asking questions about stuff you see around you, you should check out the course “Physics of the Everyday” from Brilliant. This course will help you investigate the physics of unexpected things from axe throwing to traffic jams. And by the end of the course, you’ll have a better understanding of forces, rotational dynamics, and nuclear physics.

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Thank you so much for watching, and thanks to Brilliant for sponsoring the video. [♪ OUTRO]