HIRUNDINID.E: SWALLOWS. 351 



iridescent, but sometimes lustreless. Head short, broad, and depressed; neck short. Mouth 

 capacious, its greatest width equalling that of head. 



This is a perfectly natural group, well distinguished by the foregoing characters. The 

 Swallows alone represent, among Oscines, the fissirostral type of structure ; they have a close 

 superficial resemblance to Swifts and Goatsuckers, of anotht-r order, but the relation is one of 

 analogy, not of affinity, though all these birds were formerly classed together in the highly 

 unnatural " order " Fissirostres. (See beyond, under Micropodidce and Caprimulgidce.) 



A hundred species of Swallows are pretty well ascertained to be genuine. They are dis- 

 tributed all over the world ; the most generalized types, like Hirundo itself, are more or less cos- 

 mopolitan, but each of the great divisions of the globe has its peculiar subgenera or particular 

 sets of species. Thus, all the American groups except Hirundo and Clivicola are peculiar to 

 this continent. 



Swallows are insectivorous, and therefore migratory in cold and temperate latitudes; 

 unsurpassed in powers of flight, they are enabled to pass with ease and swiftness from one 

 country to another, as the state of the weather may require. With us a few warm days in 

 February and March often allure them northward, only to be driven back again by the cold, 

 giving rise to the well-known adage : " One Swallow does not make a summer." No birds 

 are better known to all classes than these, and none so welcome to man's abode — cherished 

 witnesses of peace and plenty in the homestead, dashing ornaments of the busy thoroughfare. 



The habits of Swallows best illustrate the modifying influences of civilization on indigenous 

 birds. Formerly, they all bred on cliffs, in banks, in hollows of trees, and similar places, and 

 many do so still. But most of our species have forsaken these primitive haunts to avail them- 

 selves of the convenient artificial nesting-places that man, intentionally or otherwise, provides. 

 Some are just now in a transition state ; thus the Purple Martin, in settled parts of the country, 

 chooses the boxes everywhere provided for its accommodation, while in the West it retains its 

 old custom of breeding in hollow trees. The nesting of our Swallows now presents the follow- 

 ing categories of method : — 



1. Holes in the ground, dug by the birds, slightly furnished with soft material : Clivicola 

 riparia, Stelgidojyteryx serripennis. 



2. Holes in trees or rocks not made by the birds, fairly furnished with soft material : 

 Progne suhis, Tachycineta bicolor, T. thalassina. 



3. Holes, or their equivalents, not made by the birds, but secured through human agency, 

 and more or less fully furnished with soft material, according to the shallowness or depth of the 

 retreat. (Formerly, no species ; now, all the species excepting Clivicola riparia.) 



4. Holes constructed by the birds, of mud, plastered to surfaces, whether artificial or natural, 

 and loosely furnished with soft material. This is seen in perfection in the nesting of Petro- 

 chelidon lunifrons, and is imperfectly illustrated by the nidification of Hirundo erythrogastra. 



5. Eggs pure white, unmarked : Tachycineta bicolor, T. thalassina, Clivicola riparia^ 

 Stelgidopteryx serripennis, Progne subis. 



6. Eggs thickly speckled : Hirundo erythrogastra, Petrochelidon lunifrons. 



Aside from three extralimital species (Progne cryptoleuca, Petrochelidon fulva, and Calli- 

 chelidon cyaneoviridis), lately ascertained to occur as stragglers in Florida, the seven estab- 

 lished North American species, referable to six genera, may readily be determined by the 

 following 



Analysis 0/ Genera and Species. 

 Tail deeply forficate, with linear lateral feathers ; lustrous steel-blue above, rufous below . Hirundo erythrogaster 



Tail simply emarginate ; lustrous green ; beneath wliite Tachycineta bicolor 



Tail simply emarginate ; opaque velvety green ; beneath white Tachycineta thalassina 



Tail nearly even ; lustrous steel-blue ; rump rufous Petrochelidon lunifrons 



Tarsus with tuft of feathers below ; lustreless gray ; below white Clivicola riparia 



Outer edge of first primary serrate ; lustreless brownish ; paler below . Stelgidopteryx serripennis 



Bill very stout, curved ; male entirely lustrous blue-black .... Progne subi* 



