THE PHILOSOPHY OF MIGRATION. 



65 



however, do not necessarily indicate migratory 

 habits, for many sedentary birds possess them ; but 

 these species, as for instance many of the Raptores, 

 some of the Terns, many Humming Birds, and 

 many Swallows, all depend largely on their wings 

 for obtaining food. Let us glance at a few instances. 

 The wings of a Goldcrest or a Willow Wren are 

 long, flat, and pointed, best adapted in every way 

 for migration flight ; but the wings of a Wren or 

 of a Dipper are short, more concave, and rounded, 

 a shape most ill-adapted for long-sustained flight. 

 All, or nearly all, the Timeliid^, most of the 

 PiTTiD^, many of the Paradiseid.^, and hosts 

 of other sedentary tropical Passeriformes are 

 remarkable for their feeble, concave, short and 

 rounded wings. 



DIPPER S WING 



(Sedentary). 



TURNSTONE S WING 



(Migratory). 



This variability not only extends to the feathers 

 of the wing, but includes corresponding develop- 

 ment of the bones which support it and the muscles 

 with which it is worked. That the shape of the 



