Comparative Periods of Nestling Life 13 



among the Osciiies, only those having an extended and con- 

 tinuous song period; and apparently only in the southern 

 part of the breeding range of the Cuckoos and exceptional 

 colonial species (the northern Cuckoo seldom produces a 

 second brood though it often makes an attempt). The 

 most productive species in point of families include the 

 Tufted Puffin, Cassin's Anklet, Mourning and Ground 

 Doves, Yellow-billed and Black-billed Cuckoos, Pewee, 

 Say's and Black Phoebe, Horned Lark, English, Vesper, 

 Chipping, Field, Song and Grasshopper Sparrow, Slate- 

 colored Junco, Cardinal, Indigo Bunting, Mockingbird, Cat- 

 bird, Brown Thrasher, House and Carolina Wrens, Robin 

 and Bluebird. Apparently it does not occur to any extent 

 among the lower orders, or the Birds of Prey, A^^oodpeck- 

 ers. Kingfishers, Swifts or Hummingbirds, nor regularly 

 in the Passeres among the Crows, Jays, Starlings, Crackles, 

 Blackbirds, Orioles, Tanagers, Waxwings, Vireos, War- 

 blers, Wagtails, Creepers, Nuthatches, Titmice or Kinglets. 

 That some species are more productive than others in 

 the number of broods in a season, is of course due primarily 

 to the prolonged duration of sexual instinct, or in other 

 words, to a continuance of the peculiar physiological con- 

 dition incident to rei)roduction, perhaps often repressed 

 in the individual in the united movements of the colonial 

 species, or more often lost for the season by the less domi- 

 nant species through lessened vitality after a long period of 

 waiting upon the young. The Land Birds included in the 

 above list are birds with the requisite vitality and versa- 

 tility to adapt themselves to environmental changes inci- 

 dent to civilization, and are among the most dominant 

 species. They are all prompt, hardy nesters, therefore res- 

 ident or only absent during the colder months, with the 

 possible exception of the Indigo Bunting; all are more or 

 less independent, especially for the earlier nesting site, of 

 a camouflage of deciduous vegetation. For example, the 

 Phcebe with no other advantage over other inornate-nesting 

 Flycatchers, is enabled to produce two or more broods by 

 beginning much earlier than other members of its family, 

 and relining its nest for subsequent broods. 



