**3.1 Materials and methods**

### **3.1.1 The wild birds used in the present study**

A total of 127 wild birds, including Anatidae (n=65), seabirds (n=17), common cormorants (*Phalacrocorax carbo*, n=30), Ardeidae (n=10) and others (n=5) was used in the present study. The categories of birds included the following species: the Anatidae included spotbill duck (n=19, *Anas poecilorhyncha*), wigeon (n=15, *Anas penelope*), pintail (n=11, *Anas acuta*), mallard (n=7, *Anas platyrhynchos*), common teal (n=6, *Anas crecca*), gadwall (n=2, *Anas strepera*), common shoveler (n=2, *Anas clypeata*), wood duck (n=1, *Aix sponsa*), garganey (n=1, *Anas querquedula*) and tundra swan (n=1, *Cygnus columbianus*). The seabirds included greater scaup (n=6, *Aythya marila*), tufted duck (n=6, *Aythya fuligula*), Eurasian pochard (n=3, *Aythya ferina*), common scoter (n=1, *Melanitta nigra*) and great crested grebe (n=1, *Podiceps cristatus*). The Ardeidae included black-crowned night heron (n=3, *Nycticorax nycticorax*), little egret (n=3, *Egretta garzetta*), intermediate egret (n=2, *Egretta intermedia*), cattle egret (n=1, Bubulcus ibis) and great egret (n=1, *Egretta alba*). The others included eastern turtle dove (n=1, Streptopelia orientalis), common kestrel, (n=1, *Falco tinnunculus*), sparrowhawk (n=1, *Accipiter nisus*), peregrine falcon (n=1, *Falco peregrinus*) and Eurasian woodcock (n=1, *Scolopax rusticola*). As shown in Fig. 3, the birds were collected from various areas in Japan.

Most of the wild birds were collected as part of another National Investigation conducted by the Environment Agency in Japan (the present; Ministry of the Environment in Japan) in 1995. Other birds, which were protected in the Gyoutoku bird observatory in Chiba Prefecture, were transported to our laboratory after death.
