80 The Wilson Bulletin — No. 67. 



Gyrfalcon: Male; wing 34.42, tail 21.67, culmen 2.29, 

 tarsus 5 :99, middle toe 5.00. 



Female; wing 39.37, tail 24.49, culmen 2.59, tarsus 6.32, 

 middle toe, 5.33. 



Black Gyrfalcon: Male; wing 36.32, tail 21.97, culmen 

 2.29, tarsus 6.12, middle toe 4.92. 



Female; wing 39.80, tail 24.94, culmen 2.59, tarsus 6.68, 

 middle toe 5.33. 



Diagnostic Marks. 



Lower tail coverts always streaked with dusky (in contrast 

 with islaiidus), upper parts with white never prevailing; light- 

 er colored (but darker than island us) is Gray Gyrfalcon, 

 darker is Gyrfalcon, and the darkest form is Black Gyrfal- 

 con. 



Color Pattern. 



Adult : Top of head much streaked with white, upper parts 

 barred with blackish and grayish or bufify white, tail with 

 sharply contrasting bars of light and dark, nearly equal in 

 width ; thighs and flanks always barred with some dusky. 



Young : With much whitish above in spots, below with the 

 dark stripes narrower than the \vhite interspaces. 



The Gyrfalcon has the head more dusky and the whole 

 plumage with more extent of the dark markings. 



The Black Gyrfalcon is still darker, with the darker mark- 

 ings prevailing so that the under parts appear dark. 



Flight. 



Apparently not distinguishable from that of the White 

 Gyrfalcon. 



Food. 



Sea birds, ptarmigans, waders, rabbits, hares, squirrels, 

 lemmings, mice.. 



Voice. 



Ky ak, ke a, ke a, ke a, increasing in rapidity. 



