THE ARCHITECTURE OF SWALLOWS 391 



Architecture of Swallows 



Next after the migration, the nidification of Swallows is the 

 best-known point in their natural history. The nesting and 

 the eggs of all the "North American species have become per- 

 fectly well known, such is the abundance of the birds, such 

 their familiarity with man. Their buildings illustrate two 

 striking propositions: 



1. The versatility of architectural genius within the limits of 

 a small and perfectly natural group of birds. 



2. The influence of man in modifying the architectural cus- 

 toms of birds. 



Every one of the North American species nests in a way 

 peculiar to itself, even those which are most alike being dis- 

 tinguished by some circumstance, either of the nest itself, or 

 of the freight it bears ; and all the species, with a single prob- 

 able exception, have successively yielded to the modifying 

 influences of the gradual settlement of the country by man. 

 The Violet-green Swallow has held out the longest, and it is 

 only very recently, in fact, that we have learned of its accept- 

 ance of the new order of things. The time when the Barn 

 Swallow forsook its primitive custom of building has passed 

 out of mind ; the modification is so profound, that this bird 

 now very rarely nests elsewhere than in artificial resorts which 

 man presents to its choice. In some cases, the change is com- 

 plete in settled portions of the country, while elsewhere the 

 same species retains its primitive habits. Thus the Cliff or 

 Eave Swallow now nests habitually on buildings in the East- 

 ern United States, though it still glues its curious rnud fabrics 

 to the faces of cliffs in the West 5 and the Purple Martin nests 

 indifferently in boxes set up for its use, and in holes in trees. 

 In the case of the Cliff Swallow, another curious result of the 

 settlement of the country is seen in the gradual extension of 

 the range of the species. Formerly restricted to regions 

 abounding in natural nesting-sites, it has spread into populous 

 districts, where the eaves of buildings afford a convenient 

 substitute for the original breeding-places. The Rough-winged 

 Swallow originally nested, and generally still nests, like the 

 Bank, in holes dug by itself in the ground ; but it now often 

 avails itself of the nooks afforded by bridges, piers, and other 

 contrivances of man. I should not be surprised if this bird 

 were an immigrant, into some parts at least of North America, 



