Oystercatchers are distinctive shorebirds found across coastal regions worldwide. These striking birds are easily recognized by their bold black-and-white or all-black plumage, robust bodies, and particularly their long, bright orange or red bills. They are known for their loud, piping calls, often heard echoing across tidal flats.
Specialized Bivalve Diet
The diet of oystercatchers is primarily composed of bivalves. While their name suggests a strict preference for oysters, these birds consume a variety of other bivalves, including mussels, clams, cockles, and limpets. American Oystercatchers, for instance, feed on species like blue mussels, ribbed mussels, and various clams such as soft-shell, razor, and hard clams. In some regions, such as the UK, oysters are rarely the main diet, with mussels and cockles being more common. These bivalves are abundant in the intertidal zones where oystercatchers forage, providing a consistent food source.
Ingenious Feeding Strategies
Oystercatchers possess specialized bills, which are highly adapted for accessing their bivalve prey. Their bills are strong, flattened, and chisel-like, allowing them to employ several distinct feeding techniques. One method involves “stabbing,” where the bird swiftly inserts its bill into the slightly open shells of a bivalve and severs the adductor muscle that holds the shells together. This action prevents the bivalve from closing, allowing the bird to consume the soft inner parts.
Another technique is “hammering,” used when bivalves have their shells tightly closed. The oystercatcher removes the bivalve from its bed, takes it to a drier location, and then repeatedly strikes the shell at the point of the adductor muscle until it breaks open. For bivalves that burrow into sand, like razor clams, oystercatchers utilize a “probing” method. They insert their long bills into the substrate, using them as both a shovel and a lever to loosen and pull the clam to the surface.
The shape of an oystercatcher’s bill can adapt to its preferred feeding technique, with chisel-shaped tips for prying or blunt ends for hammering. Their bills grow rapidly, allowing them to adjust their bill shape to suit changes in available food sources. Young oystercatchers learn these complex foraging skills from their parents.
Broader Dietary Habits
While bivalves form the core of their diet, oystercatchers also consume a range of other marine invertebrates. Their broader dietary habits include:
- Crustaceans, including mole crabs, hermit crabs, and lady crabs.
- Marine worms, such as sandworms and polychaete worms, which they locate by probing in intertidal flats.
- Barnacles.
- Chitons.
- Gastropods, like limpets and periwinkles.
- Small fish.
Dietary variations among oystercatchers occur based on geographical location and the specific species. For instance, some oystercatcher species that breed inland may supplement their coastal diet with earthworms and insect larvae. Seasonal changes also influence their food choices; in some areas, bivalve consumption may shift from mussels to larger oysters depending on the time of year. This adaptability in foraging allows oystercatchers to utilize available resources effectively across diverse coastal environments.