Oystercatchers are back in force now. They are one of my favourite waders – showy and extrovert, with their piebald plumage and ringing calls. We named our present house Tjaldur, which is the Faroese word for oystercatcher and is also used in Iceland.
The Shetland word is shalder and, in Norway, the oystercatcher is known as tjeld. Sheld means part-coloured and refers to the bold black and white contrasting plumage. This colouration, along with its shoreline habitat, gave it the common name of sea pie in many parts of Britain. The name oystercatcher is a misnomer as these birds do not eat oysters. In the late 18th/early 19th century the term oystercatcher started to come into use in Britain from America. There, it was applied to the closely related American species of oystercatcher, which ate bivalves known as coon-oysters.
Oystercatchers at the coast feed on shore-dwelling bivalves such as mussels, limpets and Baltic tellins, along with other invertebrates like ragworms. There are two main techniques to opening bivalves – stabbing and hammering.
Individual birds specialise in one of these techniques, learned from its parents. Mussels close their shells by using a strong muscle called the abductor. When feeding in shallow water, the mussel shells gape slightly to allow filtration of the plankton in the sea water. Oystercatchers use their powerful bills to stab into the mussel and sever the abductor muscle so that the shellfish are forced to open up their shells and reveal their soft contents.
Hammering is a more direct method, consisting of pounding the shell with the beak until it breaks open. Limpets are detached from rocks by sharp, thrusting blows at the edges of the shell, or by hammer blows to the shell. It is not surprising that many oystercatchers display worn bill tips.
The powerful red bill of the oystercatcher is a possible reason for the characteristic piping displays. One or more birds start calling, with the head and bill directed downwards, the bill being held slightly open. These displays often occur in the spring when territorial disputes are being settled. The piping calls reach a crescendo and then tail off, rather like a clockwork toy running down. It is thought that these piping displays may have evolved as a way of re-directing emotions and avoiding fighting.
Oystercatchers are long-lived birds, and most pairs remain together year after year. In Shetland, the oystercatcher is a common breeding summer visitor with small numbers over-wintering. Breeding takes place in a variety of habitats, including clifftops, coastal grassland, fields, shingle seashores, gravel, moorland and roadsides. In 2005, when Springwatch was being broadcast from Shetland, one pair was filmed nesting in a pile of roadside gravel beside the main, busy road through Quarff.
There have been few bird records this week. A tundra bean goose was at Spiggie with another at Sandwick, and two adult Greenland white-fronted geese were also recorded at Spiggie. There were continuing records of Iceland and glaucous gulls with up to eight Icelands in Lerwick and seven at Laxo. A pheasant was reported from Catfirth and there was a male goosander on the Strand Loch.
Frogs are also returning to ponds in many areas and early spring flowers are well advanced.
Joyce J M Garden