Black-throated Diver (Gavia arctica)

This is the scarcest of the three wintering divers in the county. Their main winter habitat is normally sandy bays, where they take sandeels, crustaceans and flatfish. Black-throated Divers were recorded in two tetrads during this Atlas: off Hilbre (SJ18Z) in all three winters, counts of 1, 1 and 2 birds, and off Hoylake (SJ29A) in winter 2004/ 05, 1 bird.

As with many seabirds, the number of records has increased markedly over the years, probably reflecting an increase in observers, their use of telescopes, and indeed awareness of what birds might be just off our coasts. Coward (1910) knew only of one shot about 1853 on Puddington Marsh and one shot in the mouth of the Dee in December 1876, with another reportedly shot a week before. Bell (1962) recorded three single birds inland in 1915 and 1916, then the next at West Kirby in 1937. In January 1942 an immature male was shot near Nantwich. From 1950 to 1960 there were 16 reports, mostly from the Dee estuary from September to April, but three inland mid-winter records. Bell (1967) added a further eight records, all in the Dee.

The annual county bird reports show that in the 1970s there were about 13 winter records, two of them of two birds together. During the 1980s there were at least 28 winter records – including the record winter count for Hilbre of three birds on 7 December 1984 – although the practice in some of the bird reports of aggregating many of the Hilbre records makes it impossible to give precise totals. From about 1990 onwards Black-throated Divers have become somewhat scarcer, with 25 records in 15 years to 2005. The likelihood of finding one inland has decreased as well. From 1970 to 1993 there were 15 records away from the north Wirral, but birds were found inland in only two of the thirteen years since then: three in 1997 and one in 2002. This apparent shift in occurrence and distribution deserves study; it coincides with warmer winters, but the causes are unknown.

This species has been little studied but survey work for the BTO Winter Atlas showed that the coasts of the Irish Sea are the least likely places in the UK to find the species in winter. Perhaps 1,300 Black-throated Divers winter in Britain, the larger numbers along the east coasts probably being immigrants from Scandinavia, while those on the west of Scotland, and presumably the few that visit Cheshire and Wirral, are likely to be from the Scottish breeding population (BTO Winter Atlas).