Sensitive Beak

Long-billed Curlew (Numenius americanus)

While the Least Sandpiper is the smallest, the Long-Billed Curlew is the largest of the sandpiper family. This solitary individual foraged at low tide in the delta formed by the Schoolhouse Creek outfall. Its feeding strategy is obviously selective, the very opposite of its small cousin. It must use its eyes to locate patterns in the mud — bubbles? craters? — that indicate something edible below. It can do that even if the mud is covered by an inch or so of water. It probes with its bill, but doesn’t always go deep. The sensors in its bill tip tell it whether something of interest lies below. If so, the bird can plunge not only its beak but its entire head into the mud to grab its prey. How does it keep its whole bill from getting full of sand? It can open up just the tip of its bill to seize the little worm or crab or mollusk or whatever it finds.

Since the bird does not raise its head up high in order to swallow what it finds, how does it transport the food against gravity into its mouth? With chunky food like little crabs or clams, you can see the food travel upward as the bird rapidly shakes its head forward and backward, opening its beak when its head moves forward, and closing when back. Scientists at MIT wondered about a related question. With tinier morsels, the size of a raindrop or smaller, the scientists found that some long-billed birds exploit a feature of water droplets’ surface tension. By opening and closing their bills repeatedly in tiny amounts, they rely on “contact angle hysteresis” to defeat gravity and propel the loaded droplet upward.

Such a long beak can be a problem when it comes to preening. A few seconds into the video, the bird gives a quick tweak to feathers on its flank. It probably can’t use its bill to preen anything above its shoulders. It has to scratch to work on the higher parts. Females have it worse; they are hardly bigger than the male but their beaks are much longer.

Unlike many of the other birds we see here, curlews breed in temperate grasslands, not up in the Arctic tundra. They are relatively familiar summer birds in the Midwest, breeding on pastures, farmlands, and patches of wildlands. Their migrations are relatively short range. Source. That’s an advantage in terms of energy expenditure, but a disadvantage for habitat loss. More and more of the grasslands where they prefer to breed have been turned into suburban development. As a result, their numbers are in long-term decline, and they have all but disappeared from the Atlantic coast, but the population that remains is thought to have stabilized in recent decades.

Long-billed Curlew (Numenius americanus)

More about them: Wikipedia Cornell Audubon In Chavez Park


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