A6.106 Annex I and migratory species for which no SPAs have been selected


4. Wildfowl and other waterbirds

Although formerly widespread in historical times (Boisseau & Yalden 1998) Cranes Grus grus became extinct in Ireland by the 14th century and by about 1600 in England. It has recently recolonised England with regular nesting occurring since 1981, and birds resident throughout the year. The area of recolonisation is an SPA, but Cranes have not been listed as a qualifying species there because of uncertainty surrounding the viability of the breeding population, which is known to be derived from a very small number of birds and includes at least one sibling pair (Taylor et al. 1999). Consequently, the population may be at risk of suffering inbreeding depression. These birds also behave in a manner that is different from other Cranes in Europe since they are largely sedentary within their breeding area, although they do occasionally wander within East Anglia during spring and autumn. The reasons for this are not clear. It may be that the area provides for the birds requirements year round or this aberrant behaviour could have resulted from the possible inbreeding depression described above. Grey Herons Ardea cinerea are partial migrants in the UK. They nest locally and colonially across the whole of Britain and Ireland. Britain holds about 9% of the European total and the island of Ireland a further 3%. None of the colonies occurring in the UK exceed 1% of the European total. Ferruginous Duck Aythya nyroca occurs irregularly as a non-breeding vagrant. There are no concentrations of the species. Red-crested Pochard Netta rufina breed in the UK, but as a result of introduced stock (Ogilvie & the Rare Breeding Birds Panel 1999b). There are no obligations for SPA designation for non-native birds. A few natural vagrants occur irregularly. Smew Mergus albellus occur regularly in the UK at a small number of wetlands, although numbers are very low relative to the major concentrations in The Netherlands and elsewhere in continental Europe. No SPAs have been selected for Smew because levels of occurrence, even at sites with the largest numbers, fall significantly below the threshold of 50 used as a minimum in selecting sites for wintering waterbirds (see section 5.1.2).