With its pied plumage, pink legs, and red bill, the oystercatcher is one of our most distinctive shorebirds. It has several strange patterns of behavior, including an unusual piping display performed in the breeding season to defend its territory.
Many coastal waders are dull brown and difficult to distinguish from each other, but the oystercatcher is an exception. Its orange-red bill, red eyes, and pink legs stand out strongly from its stark black and white plumage.
However, if you come across an oystercatcher while it is quietly feeding it can seem an inconspicuous bird, particularly if its back is turned towards you. Only when it is disturbed and looks up does it reveal its beautiful colouring.
Male and female oystercatchers are similar in appearance. The upperparts are predominantly black, with white wing-bars, rump and base of the tail. During the breeding season in spring and summer the black part of their plumage becomes glossy.
In winter it is duller and the birds develop a white collar round the front of their necks. Young oystercatchers retain the white collar and duller plumage all the year round.
The adult bill is orange-red, becoming yellower towards the tip. In younger birds the tip is a dull yellow-brown. The bill is about 7cm (3in) long, the female’s being slightly longer than the male’s. The legs of the adult are pink but in young birds are greyish.
The colour of the eyes also develops as the birds mature. In their first year, oystercatchers have brown eyes. As they grow older, these become yellow, then orange and finally red by the time the birds reach adulthood. The red of the eye is accentuated, again primarily in the adult, by a ring of red feathers surrounding it.
Coastal and Inland Habitats
Oystercatchers occur in a variety of habitats, but are primarily coastal. On rocky shores they feed on both exposed headlands and sheltered bays, though the number of oystercatchers found there is never great.
Larger numbers are found on mud flats, where the birds can probe for worms and shells. On extensive mud flats, huge winter flocks numbering 10,000 or more can be seen. As high tide approaches the birds fly off noisily in flocks to roost together in dense packs above the high-water mark.
Oystercatchers have been moving away from the coast to take advantage of inland feeding sites. They are now common in farmlands, an area they didnt inhabit before. The reason for this movement is down to human disturbance of the coast.
With their name, you would think that their diet consists of oysters. However, while many do oysters, many dont. Inland birds live off earthworms and other soil invertebrates and coastal dwellers eat mostly crabs and shellfish such as limpets, cockles and mussels, though worms make up part of the diet.
The oystercatcher is adept at extracting the meat from a shellfish. It takes the shell to a rocky or sandy surface that will give good support, placing the weakest part of the shell uppermost. It will then stab through the gap between the shells or it will hammer the shell until it can get its bill inside.
Once inside the shell the oystercatcher uses its bill to sever the muscle attaching the flesh to the shell and eats the flesh.
This method of feeding illustrates some interesting adaptations. The bill is sensitive enough to detect food when probing in sand or mud, yet it is also tough enough to break through a hard shell.
Another strange feature is that some prefer to attack the shells from the left, while others attack it from the right every time, similar to being right or left-handed.
An oystercatcher attacks shells in one of two ways, depending on how it was taught by its parents. Which method it uses is reflected by its bill. If the bird stabs its bill between the shell valves the bill remains sharp, but if it hammers the side of the shell the bill becomes blunt.
The more usual call of an oystercatcher is a ‘peep’. When alarmed or excited this may be varied to a repeated ‘peepa, peepa, peepa’.
Throughout the winter oystercatchers flock together but at the start of the breeding season, they separate into pairs. Oystercatchers mate for life and establish a territory.
The courtship and territorial behaviour also include some unusual displays. During courtship a butterfly-type display is performed. The male flies over his territory with slow exaggerated wing-beats. Sometimes he pursues a female but is often alone.
Another strange behavior is the territorial display with its associated piping call. The call begins with a series of clearly spaced, loud notes. These gradually quicken until they become a prolonged trill.
At the same time the bird adopts a posture with the neck partly extended, raised humpback shoulders and the bill open and pointing downwards. A bird performing this display to defend its territory may be joined by its mate and by birds from adjoining territories to form a party of piping birds. The piping call may also be given in flight, again to defend territory.
Nest, Eggs and Young
The typical oystercatcher nest is a simple hollow or scrape, sometimes lined with stones, shells, or dead vegetation. Favourite sites include coastal shingle, rocks and dunes, and river banks and loch-sides. As inland feeding becomes commoner, so does inland breeding, with nests being established in open cultivated fields.
Egg-laying usually takes place in May, with a clutch of three. The eggs are incubated for about 25 days, mostly by the female. A few hours after hatching the chicks begin to wander, closely guarded by their parents.
If danger threatens, the parents sometimes try to distract the intruder by feigning injury or by settling into a brooding posture some distance from the chicks. More often they fly around calling, and the warning cry causes the chicks to stop and freeze in a secluded spot where their camouflage makes them hard to find.
Oystercatcher chicks are unusual among waders in being dependent upon their parents for food. This is because their bills are too small to break open shells. This dependence lasts until the chicks fledge at about 35 days old.