Fall shorebird migration is well under way, and the intertidal habitats in Maine are hosting legions of shorebirds that are passing through. Many of the species we are seeing now nested on the arctic tundra and are headed to wintering grounds in the Caribbean, Central America and South America.
Shorebird identification can be daunting. Shorebird enthusiasts scan flocks looking for a western sandpiper among the many semipalmated sandpipers, or an American golden-plover among the black-bellied plovers. It takes time and perseverance to identify many shorebirds. It is no wonder that a suite of six small sandpiper species is collectively referred to as peeps. Identifying such a shorebird as a peep is good enough for many birders.
Today, I want to recommend observing the feeding behavior of shorebirds rather than dwelling on the nuances of identification. There is great variety in the ways these birds find food. Because shorebirds are awfully confiding, they will approach still observers, affording great views through your binoculars.
The killdeer, with its large eyes, is a visual hunter. Using its keen eyes, it looks for disturbances of the sediment surface by the many invertebrates that live in sand flats and mudflats. David Duprey/Associated Press
Let’s start with the plovers. Take a look at the eyes of a killdeer, a semipalmated plover and a black-bellied plover. The eyes are strikingly large. Plovers employ a run-and-peck method of feeding. Using their keen eyes, they look for disturbance of the sediment surface by the many invertebrates that live in sand flats and mudflats. When a clam spurts water, or a polychaete worm (a segmented worm related to earthworms) sticks its head above the sediment surface, the plover will run rapidly and capture a snack.
Keep an eye out for foot-trembling by plovers. A plover will rapidly patter one leg on the surface of the mud or sand. The vibrations often induce an invertebrate to come to the surface where it is easily captured. The short bill of a plover serves its role adequately since prey are typically not captured at depth.
On to the sandpipers. All our peeps feed by inserting their relatively long bills into the sediment. The tip of the bill is richly endowed with touch receptors so prey are found by feel.
Sandpipers can open just the tip of their bill to capture prey. It is therefore easier for the bird to retract is bill from the sediment.
I love to watch foraging peep sandpipers. Many years ago, I studied the foraging behavior of semipalmated sandpipers in the upper Bay of Fundy. Most of these arctic-breeding birds wend their way to the Bay of Fundy each fall to fatten for a long migration to the Amazon delta in South America.
The sandpipers are attracted to the area by the abundance of a small crustacean called corophium in the expansive intertidal flats. Corophium is about half an inch long, live in U-shaped burrows in the mud and can attain densities of 5,000 per square foot. Lots of food for hungry sandpipers.
At low tide, I walked down into the intertidal zone and found a place to stand near foraging birds. They frequently walked right past me so I could easily watch their feeding. About every third or fourth probe, a sandpiper would successfully capture a corophium. I could see the corophium splaying its seven pairs of legs as it struggled to escape the bill of the bird. It was easy to see a gulp in the throat of the bird as it swallowed the prey. Give this technique a try.
Sanderlings use taste to find areas in the sand or mud where their prey are found. Researchers prepared sediment with no prey and sediment where prey had been allowed to live to season the sediment, but were then removed. In the lab, sanderlings probed more often in the sediment where prey had been.
Short-billed dowitchers and stilt sandpipers forage in water up to their bellies while rapidly probing in a behavior known as stitching.
Greater and lesser yellowlegs wander in shallow water using their long bills to stab at prey, much like a heron.
Herb Wilson taught ornithology and other biology courses at Colby College. He welcomes reader comments and questions at whwilson@colby.edu
Copy the Story LinkSend questions/comments to the editors.
