A short walk along the coast path brings me to Yns Barri beach - a hidden beauty-of-a-bay that rewards those prepared to hike. I stop on the cliff-top above to admire the view and spot movement on the rocks below; black, white and red flash back at me. Oyster catchers browse on a small island of rock on a rising tide. Their black and white plumage and startling crimson beak stand out from the dark background. Swell surges at the rock, rising up the legs of one bird, sometimes reaching its belly. It pipes in protest and flaps up and on to a dry rock, shaking out its feathers in displeasure. It is searching for limpets that have released their tight grip on the rock to graze as the tide returns (read all about the lives of limpets in my previous blog post “The power of limpets”). The slightest gap between shell rim and rock will allow the oyster catcher purchase to prize it off. Once off it is flipped upside down and the juicy flesh plucked out. A mussel may be similarly dispensed with, as the bill tip is thrust between the two shell halves and the strong muscle that clamps them shut is sliced with a deft jab of the chisel -like beak. Alternatively they may hammer on the shell, cracking it open. I watch as two birds march around the shore testing limpet shells, occasionally going to work on one. These two are clearly shellfish specialists with an opportunistic streak as I see one carry off something long and thin and wriggly - most likely a blenny, a common rockpool fish.
Numerous elegant studies of oystercatchers show that the bill becomes shaped according to their feeding behaviour. ‘Stabbers’ and ‘chiselers’ have laterally compressed bill tips, whilst ‘hammerers’ have a distinctly blunt bill tip; each characteristic is created by the abrasive action of handling the hard shells of their prey. Others have a preference for worms over shellfish and have pointed, tweezer-like bill tips caused by the even wear of probing in to sand or mud. Diet preference thus results in a bill shape that is wonderfully suited to securing a successful meal. Oystercatchers seen working limpets on the shore will have honed both skills and bills with practice, yet they remain flexible if the need dictates. Their bills are uniquely specialised for coping with wear and grow at an impressive 0.4mm per day (three times faster than human finger nails). Such swift growth means that the bill can change shape rapidly to suit feeding style, allowing them to switch from worm-eaters to shellfish hammerers to stabbers and back again through the course of their long lives. Like many seabirds oystercatchers are renowned for their longevity and may live as long as 40 years so it pays to be flexible in a changing world.
By now you may be wondering how they got the name oyster catcher when no mention of oysters has been made. Their modern name is thought to be an 18th century Americanism as their New World counterpart the black oystercatcher does in fact feed mainly on oysters. Before this name stuck they were called sea pies referring to their pied plumage; the name by which they are still known in Welsh- Pioden Fôr. So next time you’re at the coast keep your eyes open for flying sea pies, you’ll probably hear their loud piping first accompanied by a charismatic burst of black and white plumage and heavy crimson bill.
By the sea in Wales at least, pies do fly…