NON-INDIGENOUS BRITISH BIRDS. 143 



States, and throughout British North America and 

 Alaska, up to the h'mits of forest growth. 



Breeding habits : The American Goshawk is only 

 a migrant from the colder portions of its breeding area. 

 Its favourite breeding haunts are in pine and other 

 woods, bluffs (small clumps of trees on prairies), and the 

 outskirts of forests. In its habits it is not known to 

 differ from its Old World ally, from which it is possibly 

 only sub-specifically distinct. The flat open nest is 

 generally made in a fir tree, on a horizontal branch close 

 to the trunk, and is made externally of large and small 

 sticks, and lined with dead leaves and flakes of bark. 



Range of egg colouration and measurement : 

 The eggs of the American Goshawk are from three to 

 five in number, three or four being generally found, and 

 sometimes only two. They are pale bluish-green, and, 

 so far as I can determine, never show any traces of 

 spots beyond an occasional nest stain. Average 

 measurement, 2-2 inches in length, by 17 inch in 

 breadth. Short eggs are generally the broadest, and 

 vice versa. Incubation is performed chiefly by the female, 

 but the duration of the period is undetermined. It 

 is probably the same as that of the Pal^earctic species. 



Diagnostic characters: The eggs of the American 

 Goshawk cannot be distinguished from those of its Old 

 World ally, nor from certain and unspotted varieties of 

 those of some other species. 



