Wood Thrush

Hylocichla mustelina (Gmelin)

The high incidence of cowbird parasitism on the wood thrush in Iowa and Minnesota noted earlier (Friedmann, 1963:73–74) is repeated in Illinois according to Graber, Graber, and Kirk (1971:16). They write that, from their own records and from the literature, they have egg data on 69 nests, 33 of which (47.8 percent) were parasitized. Their records cover various parts of Illinois, and the incidence of parasitism is similar in all areas covered. The Western Foundation has 97 sets of eggs of the wood thrush, 6 of which (6.2 percent) have 1 or more cowbird eggs. The Cornell University files have data on 409 nests of this thrush, 55 of which (13.4 percent) were parasitized; the Ontario nest records files show a higher incidence of parasitism—36 cases (30.5 percent) of 118 nests. Harrison (1975: 204) found an even greater frequency in Pennsylvania, where 11 out of 12 nests observed had cowbird eggs.

HERMIT THRUSH