Catch Me If You Can – The American Oystercatcher

Originally published on Audubon Guides on October 1st, 2012

Catching an oyster only seems difficult to me if you’re tossing one around with your kid in your backyard. For a predator the difficulty is not chasing one down but prying one apart once they’ve located it. The two sides of the bivalve’s shell are bound together by an adductor that protects them from prying intruders. Hopefully.

Considering the difficulty of which it is to open an oyster for a human, the American Oystercatcher (Haematopus palliates) is a devastating effective predator of mollusks of all sorts. Juvenile oystercatchers are taught certain techniques by their parents that make a quick meal of mollusks. They are aided by a stout, powerful bill with triangular shaped mandibles in cross section that are reinforced in such a way that they will not bend easily when attacking prey.

American Oystercatcher © Pete Corradino

One method taught, known as “stabbing”, is to sneak up on the oyster while the shell is open even the slightest, stab at the adductor and break the shell open, exposing the meal inside. The second method, “hammering”, is to pry the oyster from the oyster bed or other place of attachment and then use the bill to shatter a hole in the shell. They can then break the adductor and eat their meal.

American Oystercatcher © Pete Corradino

In addition to oysters they feed on a variety of shellfish, crabs and tube worms. Crabs are flipped on their back and stabbed to death with the bill. To locate tube worms, sensitive nerve endings in the bill allow them to sense prey as they probe the tidal flats.

A Willet attempts to drive off an Oystercatcher © Pete Corradino

Occasionally confused with the Black Skimmer (Rynchops niger), the oystercatcher’s mandibles are equal in length compared to the skimmer’s disproportionate upper and lower mandibles. The oystercatcher has a black head, white belly, and sturdy pink legs.

As willets and sandpipers scooted along the surf, the oystercatcher above methodically probed the sand for lunch, ignoring the beachgoers. When you’re a stabber or a hammerer who’s going to mess with you?

Skim a Little Off the Top - The Black Skimmer

The bill of a bird often says a lot about how a bird feeds and what they feed on. If you’d never seen a Black Skimmer (Rynchops niger) before you could certainly tell they have a unique beak. The upper mandible is considerably shorter than the lower mandible. They don’t sift their food like a spoonbill. They don’t probe the mud and worm holes like an ibis. They don’t tear their food like a hawk.

Just as their name would suggest, they skim for their food. Flying low over the water, the skimmer places the lower mandible beneath the surface and continues to fly until it feels something touch the bill – and then snaps the bill shut. Amazingly, when the skimmer catches fish or other prey species, the head drops into the water and points to the tail end of the bird. The bird maintains flight, lifts the head back out of the water continues the hunt.

The lower bill of the Black Skimmer is constantly growing to combat wear from friction as the bird skims the surface of the water. The upper mandible does not grow at the same rate, resulting in an asymmetrical appearance. The difference in length of each mandible makes picking up objects with the bill more difficult. The upper and lower bills of juveniles are roughly the same until the bird matures.

The eyes of the skimmer are largely ignored by casual birders as they’re relatively small compared to the stout size of the rest of the bird. The eye has a pupil similar to that of a cat or an alligator and can be closed to a vertical slit. This type of eye is best for night foraging.

This flock of about 200-250 Black Skimmers was located on Bunch Beach in Fort Myers. The somewhat secluded sandbar is a preferred resting spot for skimmers, godwits, turnstones and other shorebirds. As I paused to take a photo, a jogger detoured towards the birds. Oddly, the skimmers took flight while other species remained. After a moment, the skimmers circled back and rested again on the sandbar.