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The Shorebird’s Buffet

TIP: Watching how and where shorebirds eat can help you identify them

Posted: August 4, 2011 - 5:35pm

The first time I noticed that a shorebird had a specialized bill, I thought I was looking at an alien.

I was volunteering for a wildlife rehabilitation center in Chicago. Someone brought in an American woodcock, a forest-dwelling shorebird slightly smaller than a pigeon. It has a straight, slender bill about three inches long. As I held it before its check-up, the top half of its bill started to move. Just the front third of the bill curled toward the ceiling, like a person crooking a finger. I stared, speechless. I had never heard of a bird with a flexible bill. I had always thought of bills as nearly solid as bone.

American woodcocks, and the similar-looking Wilson’s snipe in Alaska, have a very good reason for such a bizarre ability. They use their bills to poke into soil and mud in search of prey such as earthworms, insects, or mollusks. Like many other shorebirds, their bills have nerve endings in the tips that allow them to find prey by touch. The birds can bury their bills in the ground, feel a tasty morsel, then use the bendable tips of their bills, like tweezers, to grab it.

The Wilson’s snipe, with its stocky body and long bill, is fairly distinctive even if you don’t see one feeding. The real test is to identify a variety of shorebirds when they are all mixed together.

The first wave of shorebirds is already moving south from Arctic breeding grounds, so now is a good time to practice picking out birds from the lineup on local mudflats, such as those found on the Mendenhall Wetlands State Game Refuge.

Shorebirds have worked out a system of dividing and conquering the mudflats and shorelines where they feed. Each species has its own section of the cafeteria depending on its utensils. The smallest species with the shortest bills feed near the water’s edge or above. The larger the bird and the longer its bill, the further out into the water it can feed. This is a case where a wildlife spy can — literally — use a profile to help identify suspects from a distance.

Sandpipers and their cousins spend much of their time digging in mud. Many of these birds have nerve endings in the tips of their bills that are sensitive to touch or smell (they have chemical receptors). These special sensitivities allow the birds to search for food at night, important for creatures that depend on the tides to expose food.

But what exactly are they eating in the mud? Popular snacks are polychaete worms (segmented marine worms) of various sizes that burrow into the mud. Tiny clams, shrimp-like invertebrates called amphipods, and insect larvae may all be buried in the top few inches of mud. What we call “dirt,” a shorebird calls dinner.

Least sandpipers, as their name states, are the smallest sandpipers found in Alaska. Their short, bright yellow legs are distinctive — when they aren’t covered by mud. They also have short bills. These birds feed highest up on the mudflats, sometimes up into the vegetation, like the youngest sibling that can’t go out into the deeper water. They often stand in a crouching posture.

Western sandpipers have black legs and are slightly larger than Least sandpipers’. The two birds sometimes overlap feeding areas. A few years ago, biologists discovered that Western sandpipers depend heavily on a food source no one knew birds could eat. This paper-thin layer of slime, composed of algae, bacteria and other organic matter, is politely called “biofilm.” Western sandpipers have bristles on their tongues and special structures in their bills that allow them to graze on biofilm. Surprisingly, it apparently makes up more than half of Western sandpipers’ diet. They tend to move a little slower as they slurp up the goo than when chasing moving prey.

Phalaropes are some of the only small shorebirds that regularly swim like ducks. You may spot them on ponds. They have a special trick of spinning rapidly in tight circles, creating a miniature whirlpool that pulls bits of food up to the surface where the bird can daintily pluck them from the water. Oddly, it seems that individuals tend to be right-turners or left-turners, like people are left-handed or right-handed.

Dowitchers are medium-sized sandpipers that have long bills for their size. With longer legs than the smaller sandpipers, they venture further into the water. They rapidly poke their bills in and out of the mud in a distinctive sewing-machine motion.

Larger birds, such as godwits and yellowlegs, tend to wade the furthest out and dig deeper for larger prey than their smaller cousins. Several species of godwits, with their elegantly long, upturned bills bob their heads up and down as they hunt for buried prey. Yellowlegs have long legs for their body size but only medium-sized bills. They often wade into deeper water and swish their heads from side to side, snapping up small fish.

Plovers are a group of shorebirds that have a different strategy than the sandpipers. Rather than poking in the mud and feeling around for food, they use their keen eyesight and thick, stubby bills to snatch food. With large eyes, all the better to see food with, they can sometimes even forage at night. Large eyes let in more light. They also have a high number of rod cells in their eyes, allowing them to detect movement in low light.

Pacific golden-plovers are large plovers that highlight these traits. Like other plovers, they often run a short distance, then stop and stand very upright, as if someone called them to attention. This is when they are peering around for movement betraying the presence of tidbits such as polychaete worms or insects.

Plovers have one other trick they use to capture prey. On mudflats, they will sometimes do a toe-tapping dance: they lift one foot slightly and rapidly jiggle their toes to disturb the mud, startling small prey into moving.

With close scrutiny of clues such as bill size, movement style, and feeding location, you can delve into the identities of the shorebirds passing through on their way to rendezvous in warmer climes.

 

• Beth Peluso is a freelance writer, illustrator, and avid birder. She enjoys spying on wildlife around Alaska.

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