Posted by: atowhee | October 7, 2021

BEAKS ARE AMAZING ANALOG DEVICES

Birding around Bodega Bay in Sonoma County encourages you to enjoy and admire the variety and vitality in the realm of the bird beak. Let us look on godwits and pelicans for the nonce.

Both birds are found around water in fall and winter. Both birds must observe and respond to the lessons of the tidal pattern. Brown Pelicans cannot dive into six-inch deep water. Godwits can’t probe into six-inch deep water and still reach the mud. The pelican needs water deep enough to soften its plunge and then float its bulk. The godwit needs to get a bit of its beak into the mud or sand for food. Some other shorebirds are able to feed on the surface: plover, avocet, stilt, etc. The godwit is a driller, a miner into mud or sand.

“Pelican Pandemonium” will be henceforth referred to as “Pelimonium.” And it is that churning, diving (by the brownies only) and pouch-packing behavior of these energetic fishers. Does the White Pelican see what it trawls for near the surface? Does the Brown Pelican see what is it diving at from two feet off the surface and at a 45-degree angle?

Here’s how Birds of the World online describes brown pelican feeding: “Captures fish mainly by surface plunging. Sights prey from air, then dives head-first from heights as great as 20 m. During dive, withdraws head over shoulders, pulls legs forward, and bends wings at wrist; also rotates body to left, probably to avoid impact injury to trachea and esophagus, which are fixed on right side of neck. As bill enters water, thrusts legs and wings backward, accelerating movement of bill toward prey. Gular pouch expands with up to 10 l[iters] of water.” That’s 2.6 gallons in the Brown Pelicans’ maw.

Later that water is pushed out by the tongue ansd tightening throat muscles. Then the beak’s contents slide down the throat as the head is thrown back and the throat opened up. Think what the digestive system must then deal with–seaweed, fish scales, fish bones, fish slime, a bit of plastic or fishing tackle, a wine cork, maybe some moluscs and crustaceans…

So we may assume that pelimonium finds several individual birds diving and pouch filling while others in the crowd paddle, wing fluff, bob their heads or simply float along. Pelicans are vocally silent birds so the noise is splashing and wing thrashing.

The Marbled Godwits line up along the bay where the water is less than four inches deep. While pelicans visually hunt, godwits hunt blindly. Their eyes can only help them determine how deep the water is. Can you imagine an analog probe that combines the sensory data of your forefinger, your tongue and your nose? It’s not imaginery, it’s the beak tip on a godwit. It’s sensitive to vibrations, chemicals, flavors, hard surface contours. Plus, that beak can open at the end like a pair of delicate tweezers. If vibrations sent out through the mud bounce back from a mollusc shell, the information leads to a beakful probe.

So pelicans and godwits and many other shorebirds can often share the same habitat. Yet their feeding is entirely adaptive for each species. Pelimonium is not like a flurry of gulls surface feeding or turnstones flipping seaweed or avocets sweeping their beak across the surface. To each his own.


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