!" "!# $% ## & ' ( ) $% " & #* ( Total numbers of Red-throated Divers recorded respectively) (Webb et al in prep b). Subsequent by WeBS in Great Britain in 2001/02 were surveys (WWT data) have suggested that this notably high, and very close to the highest yet mid winter peak may be a regular occurrence, recorded by Core Counts (1,361 in December but that the divers at this site may be very 1995), primarily as a consequence of a large mobile, distributions changing markedly over count in Cardigan Bay in December 2001. short periods. Aerial surveys of Liverpool Bay Counts in 2002/03 were unexceptional. British (covering a strip extending 20-25 km from shore totals during these winters showed a similar between Anglesey and Morecambe Bay) in pattern, with a marked increase in numbers 2001/02 and 2002/03 recorded counted maxima from September reflecting the southward of 226 divers (presumed all to be Red-throats) in migration of British and Scandinavian breeding January 2003, when 130 were recorded in birds. Numbers peaked in December/January Colwyn Bay; application of distance analysis though the decline to small numbers in summer suggests that peak numbers were 1,599 in the varies in its timing, and moderate numbers may first winter (with 95% confidence intervals of be recorded as late as May, particularly on the 1,063 to 2,405 birds) and 1,210 (901-1,626) in the Scottish east coast. Given that British-breeding second (Cranswick et al 2004, Webb et al in birds are already on territory by early spring prep a). Aerial surveys off the Norfolk/ (Migration Atlas), these are likely to be birds Lincolnshire coasts, the eastern Scottish Firths, from Fenno-Scandia or Greenland. The pattern Orkney and the Outer Hebrides have also of counts was similar in Northern Ireland but, as revealed that notable numbers of divers occur usual, involving much smaller numbers, there and, though counts in these areas were reflecting the generally lower numbers of Red- generally of fewer than 100, significantly, a high throats off the coast of the Province (1988-91 proportion of divers were located 10-20 km from Winter Atlas). shore (Cranswick et al 2003, Dean et al 2003, An increase in the number and extent of Dean et al 2004). aerial surveys – specifically to assess abundance Such findings have greatly changed our and distribution of waterbirds in UK nearshore understanding of Red-throated Divers wintering waters – has provided much new and in British waters: the British estimate (of just remarkable information on divers and seaducks 4,850 birds) is clearly a considerable wintering in Britain. In particular, surveys of the underestimate and is need of revision; the idea ‘Greater Thames’, covering the area between that birds are largely coastal or do not occur in the Essex and Kent coasts, since 2002/03 have large concentrations vulnerable to events such revealed a far greater number of divers, and as oil spills (eg Migration Atlas) also needs over a far greater area, than previously refining; and, notably, there are clear suspected (Hall et al 2003). A peak of 1,831 birds implications for both appropriate monitoring were counted in January 2003, the majority and site protection. Procedures for identifying located many kilometres offshore (Fig. 56). marine Special Protection Areas (SPAs), likely to Many birds recorded during aerial surveys are encompass large areas in the case of divers, are not identified to species (because of the speed currently in preparation (McSorley et al 2004, of the plane), particularly in the case of divers, Webb et al in prep a, Webb et al in prep c). but of the 20% identified in January 2003, all Occurring on Annex 1 of the EC Birds Directive, were Red-throated Divers; the total of 1,831 has all nationally important sites for Red-throated thus been assumed to comprise only this Divers qualify for consideration for SPA species. Further, aerial surveys adopt a ‘distance classification (Stroud et al 2001), but it may be sampling’ method, only counting a proportion of that the Greater Thames is internationally the birds actually present; consequently, it has important for this species, despite the large been estimated that the actual number of Red- increase in the international threshold (based on throated Divers in the Greater Thames in a breeding estimate of up to 140,000 pairs; January 2003 was 11,089 (with upper and lower WPE3). Only a few sites in Northwest Europe confidence intervals of 8,115 and 15,154 hold comparable numbers, eg 23,500 divers (a mixture of Red-throated and Black-throated) are the larger numbers in the Greater Thames, but found in the East German Bight (Skov et al the high counts regularly noted from the Suffolk 1995), although these occurred over a much coast, eg 2,680 off Minsmere in January 2000 larger area (13,000 km2) compared with those in (Rafe 2000), almost certainly involve the same the Thames (2,500 km2). birds also. Of particular interest is the count off These findings also have implications for the Lade Sands – especially since large numbers interpretation of the table of key sites. A major have occurred at this site and nearby Dungeness consideration is that because of the regular previously – which points to a possible occurrence of significant numbers of birds concentration in the English Channel. further from shore than can be detected by land- As around the Thames, moderate numbers based observers, all counts are likely to be of Red-throats have been noted by WeBS at undercounts to a greater or lesser degree (note, several sites around Liverpool Bay in recent in addition to those flagged because certain years, all part of a broad distribution of birds in sectors of large sites were not counted during an area stretching from Conway/Lafan Sands to WeBS, brackets in this table are applied the Ribble (Cranswick et al 2003). Clearly, the subjectively to counts that simply appear definition of sites used for WeBS Core Counts markedly low compared with previous peaks, may not be appropriate for marine species such given the difficulties of obtaining accurate as divers – although enclosed bays and counts). Nevertheless, large numbers are estuaries, such as the Clyde and Loch Ryan, are recorded periodically at many of these sites, obvious exceptions – and it should be noted that probably in relation to mobile food sources and the areas designated within the current network sea or weather conditions that may only of SPAs and Ramsar sites for UK estuaries and infrequently bring birds within sight of land, and coastal sites rarely cover the area used by divers in many cases may be indicative of larger and seaducks. It is clear that, although much concentrations further offshore. (Such land- further work is needed to provide a fuller based counts are also useful since the kilometre understanding of waterbird numbers and closest to shore cannot be covered by aerial distribution in nearshore waters, aerial surveys survey at some sites). Birds seen off the Dengie have in just a few winters greatly increased our and Pegwell Bay relate to local movements of knowledge of divers wintering in the UK. Relative density 0 0.001 - 0.344 0.344 - 1.164 1.164 - 2.562 2.562 - 4.499 4.499 - 8.436 +,- .'/ !"#$!#&' (() * (() *! ! ! !" "!# $ $ 0 1 23 & #$! , , , - &(-. ' &(-. • 0 1 23 & /0 , , , + & .. + & ( ' &( • 1 )+ (( )++ + )++(( ) 2 ). – 30 +( . ( +) ) 4 . /5 )+ (( ( -(( (( ' ))) • $!/ .( )++ ) )+ ( 6 ( • 1 7! )( +. )( () ( + )( 2 ( 890 7 ) • 3 : )- ) 1 ) 7 . ' ( 7!: + ( .) ( 2 (( 1!;!1! - ( )) ) 5 + 579 ). , , , , . $!<! ) 2 6: + )) ( . ' • 0 1 23 & ) 0/! + ). ) ' ) 0 ) ( ( ( 7 ) • /!7 )+ ( + . 1 5/! ( )- ( )- + ( ) • -3 , 4 5-16 , 7 "!" ""!# !" "!# *=8/ - ' 39 0 - ' /! ,119 7 /! )+ 2!23 - 6 6 23 &7 17 6 329 8 9: ; !" "!# $% .$ '+4 ) $% " ( 03 The fewer than 200 pairs of Black-throated gathered at pre-breeding or pre-migration sites. Divers breeding in the UK are boosted in winter Small numbers were recorded throughout the by arrivals from Fenno-Scandia (Migration summer, and nine present on the Firth of Forth Atlas). Peak totals recorded in Great Britain by in July 2002 were noteworthy. In 2002/03, fairly WeBS Core Counts during 2001/02 and 2002/03 constant numbers were recorded between were relatively low, having fluctuated between October and January, and the February peak 39 and 145 over the most recent five winters. was sustained into March. The difficulty in counting this rarest of our diver The majority of key sites are in northern or species, not least due to the remote nature of western Scotland. The count in Scapa Flow, many of the prime wintering areas, means that Orkney in winter 1998/99 remains the highest of only a small proportion of the true number is the most recent five years, although this was counted by WeBS, with a tendency for sporadic made during a dedicated survey; the count in counts with considerable variation. A number Gerrans Bay in February 2003 was the first by of key sites were not visited in the two most WeBS to exceed 50. Numbers at the latter site recent years, and many sites feature in the table have consistently exceeded the qualifying level, below by virtue of data received from but it forms just part of the South Cornwall supplementary counts and dedicated surveys. Coast Important Bird Area which held 160 A January peak in 2001/02 was exceeded Black-throated Divers in 1999/2000, with other by a second in March, presumably as birds key concentrations in St Austell Bay, Veryan Bay + and Gerrans Bay (Geary & Lock 2001). Relatively few Black-throated Divers have been Numbers, as usual, were very small in Northern recorded by aerial survey to date, though partly Ireland, although Belfast Lough remains a site this reflects the absence of survey in key areas.