17th October 2018
Established 1872. Online since 1996.

Migrant bonanza over

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CONSIDERABLY fewer migrants have been recorded this week after last week’s bonanza. The first summer male surf scoter was still at Catfirth along with two common scoters. A golden oriole and a hawfinch were reported from Busta House, while there have been up to 20 crossbills at Kergord. Other notable migrants include marsh warblers at Sandwick and Wester Quarff, a marsh harrier around Veensgarth in the Tingwall valley, and a fine male red-backed shrike at Cunningsburgh.

Red-backed shrike are fairly common passage migrants with about 75 per cent of the Shetland records since 1970 occurring in the spring, when up to 50 individuals may be recorded. About a third of these records come from Fair Isle and spring arrivals in Shetland are probably migrants on their way to Scandinavia. Red-backed shrikes breed from Western Europe to central Siberia, wintering in eastern and southern Africa. Once common and widespread as in Britain, it is now almost extinct as a breeding bird. Breeding popula­tions began to decline from the late 19th century onwards. There are around 15 con­firmed breeding records for Scotland since 1977; one of these being from the Pool of Virkie in 1990.

A red-backed shrike is about 18cm in length, larger than a rock pipit but smaller than a starling. The male lives up to the common name, having a bright chestnut back, contrasting with pale pink under parts, white throat, pale blue-grey crown and rump and a broad black “bandit-like” mask across its eyes. The tail is black with white outer feathers, and the bill is slightly hooked. Females are duller, lacking the striking head pattern, and have vermiculated, yellowish-white under parts. Red-backed shrikes mainly feed on large insects such as bumble bees and bluebottles in Shetland, but will also take small birds, mammals and reptiles. These birds perch upright, scanning for prey, dashing from their perch to capture their victims.

Some­times they store surplus food by impal­ing the corpses on thorns or barbed wire.

Since the beginning of the month there have been several sightings of killer whales, good news for researchers Andy Foote and Volker Deecke who are studying the populations around Shetland. At an interesting talk at the Shetland Amenity Trust offices on Friday 13th, they provided an update on last year’s research and outlined plans for this season’s work.

It is estimated that there are around 148 killer whales around the islands, including the offshore mackerel-feeders which are seen around fishing boats in groups of up to 50 animals. Killer whales can be identified individually by the shape and size of their dorsal fin and the shape and size of markings on their backs and sides. Over 1,000 individuals in the North East Atlantic region have a photo ID record. About 60 have been identified around Scotland and it appears that the killer whales on the east and west coasts form two distinct populations. Slightly over 50 per cent of the killer whales seen around Shetland in the summer months are coming back here each year.

Research from British Columbia has shown that killer whales form separate populations along the coast and that resident populations feed on fish, favouring chinook or king salmon. Other groups move into the area only occasionally and these are mammal-eaters, their main prey being harbour seals (another name for the common seal). Different populations have different underwater calls so, by analysing the structure of the calls, it is possible to judge whether animals belong to the same population. This summer’s research aims to locate and photograph as many killer whales as possible, checking individual characteristics against the photo ID bank, and also listening to pods calling underwater using hydrophones. If anyone observes killer whales they can contact the team on 07500 380524.

Joyce J M Garden