Allen on an Inadequate "Theory of Birds' Nests." 25 



most readily available for their construction being not everywhere 

 the same ; they also vary in accordance with the climatic conditions 

 of the locality, the same species building a quite different nest, as 

 respects warmth and stability, in the colder portions of its habitat 

 from that which it constructs in the warmer portions. 



But while these deviations under diverse circumstances readily 

 explain variation in the situation and character of the nests of the 

 same species, they fail to explain why closely allied species, living 

 together under precisely the same conditions of environment, and 

 sometimes so closely resembling each other in size, color, and all 

 external characters as to require the eye of an expert to detect their 

 specific diversity, should build totally unlike nests, and display 

 almost the widest possible differences in respect to their situation. 

 To cite, in illustration, a single example from the many that might 

 be given, we may instance our common Pevvees and Flycatchers. 

 In this small group we find a wide range of diversity in breeding 

 habits among species most intimately related in structure and gen- 

 eral habits. The Least Pewee builds a small, compact, felted nest 

 of fine soft materials, and its nearest allies, the Acadian and Traill's, 

 build far ruder and much more bulky structures of coarse grasses, 

 strips of bark, and other similar materials. Another near relative of 

 these species, the Wood Pewee, selects for its nesting-site a lichen- 

 covered dead branch, on which to saddle its small, highly artistic, 

 cup-shaped nest, covered externally with lichens glued to the surface 

 in such a manner as to render the structure almost indistinguish- 

 able from a natural protuberance of the branch itself. The Bridge 

 Pewee, another allied species, builds a large bulky nest, formed 

 outwardly of a heavy layer of mud, copiously lined with dry grass 

 and feathers, and shelters it in the chinks of walls, under shelv- 

 ing rocks, in sheds, outbuildings, and under bridges. The Great- 

 crested Flycatcher chooses hollow trees or deserted Woodpeckers' 

 holes in which to form its nest and deposit its eggs, while its allies, 

 the Kingbirds (genus Tyrannus), build large open nests, which they 

 make no attempt to conceal. 



Notwithstanding all this diversity of situation and structure 

 among closely allied species, birds' nests have been divided into 

 two classes, according to " whether the contents (eggs, young, or 

 sitting bird) are hidden or exposed to view," and the broad general- 

 ization based thereon that the character of the nest is intimately 

 related to the color of the female parent-bird. This, in fact, is Mr. 



