prelease for Mute swans from Western Europe to GB and from Eastern Europe to Italy is medium (Table 6). H5N1 was confirmed in 16 Mute swans wintering in the south of Italy in 2006 (Terregino et al. 2006). Those birds are believed to have migrated from the Black Sea region of eastern Europe. The prediction of a low prelease for Whooper swans arriving in GB albeit from Western Europe (Table 6) is interesting in the light of the H5N1-infected bird found dead on the east coast of Scotland on 29 March 2006 (Blissitt 2007). It is possible that the swan was actually infected within GB and that it was effectively a sentinel – dead swans being large and white are conspicuous (Newmann et al. 2009). Indeed, most Whooper swans in GB come from Iceland in October rather than March (Brazil 2008). It could, however, have been infected in continental Europe and then flown to Scotland. Indeed, the probabilities of H5N1-infected Whooper swans’ surviving migration from Western Europe and still shedding virus on arrival in GB are high. It should also be noted there was an outbreak of H5N1 in the Baltic Sea in February 2006 with increased mortality among Mute swans and Whooper swans (see Teifke et al. 2007) such that the local pprev at that time would have been high. Mixing of different wildfowl species is well documented (see Fig 15 of Rees 2006). Horizontal transmission from one bird to another in the migration chain is difficult to incorporate in this release assessment. However transmission through a “baton effect” between different individual birds at stopover sites would be accommodated by the values of pprev used for Western Europe, Eastern Europe and NAEA in this release assessment. Although there are quantitative data available for many of the parameters, a qualitative approach was adopted here because of the uncertainty both in the geographic ranges of the birds and the timings reflecting the lengths of the stopovers
Table 2: Numbers of migratory birds (per year) entering GB, the Netherlands and Italy calculated as the difference between totals of monthly counts (maximum - minimum) HRS Bird Species GB, Wetland Bird Survey data of Austin et al. (2008) The (Hustings et al. 2008) , peak national count in January between 1990 and 2005. Atkinson et al. (2006) Bewick’s Swan Cygnus columbianus 3,775 13,000 0 Whooper Swan Cygnus cygnus 7,428 2,000 0 Mute Swan Cygnus olor 11,542 5,000 3,248 Greater White-fronted Goose (European race) Anser albifrons albifrons 1,341 600,000 11,049 Greylag Goose Anser anser 72,980 150,000 5,392 Red-breasted Goose Branta ruficollis 4 7 4 Eurasian Wigeon Anas penelope 324,097 600,000 123,936 Common Teal Anas crecca 126,498 50,000 97,529 Mallard Anas platyrhynchos 97,872 180,000 208,000 Northern Pintail Anas acuta 25,344 20,000 12,781 Garganey Anas querquedula 38 (May) + 47 (Aug)* 80 (Apr) + 110 (Aug)* 223 Northern Shoveler Anas clypeata 11,200 10,000 22,811 Common Pochard Aythya ferina 24,160 45,000 42,189 Tufted Duck Aythya fuligula 46,429 150,000 7,725 Black-headed Gull Larus ridibundus 150,555 150,000 217,468 *Spring and autumn migration Table 3: Qualitative estimation of number of HRS species migrating from different regions of the world to GB, the Netherlands and Italy (per year) (n). Negligibles are excluded. W/E E/E NAEA WA ESA