ISLAND BIRD-LIFE 37 



Some of these islands are mere rocks or sandbars, with 

 few or no human inhabitants and consequently by just so 

 much, are the more habitable for birds. But if we should ex- 

 tend our survey to those larger bodies of land on which true 

 island conditions exist, we should find the results of this pro- 

 tecting influence even more strongly manifested, as where a 

 family has been preserved in the Greater Antilles or an en- 

 tire fauna in Australia. 



Long-continued insular isolation, often under special 

 conditions of environment, has resulted in the development 

 of new species. We shall find evidences of this kind of evo- 

 lution in the Bahamas, but northward on our coast, if we ex- 

 cept certain slightly differentiated forms in the Bermudas, 

 only Sable Island, off Nova Scotia, appears to have pro- 

 duced a bird of its own ; the Ipswich Sparrow being restrict- 

 ed to this islet, where possibly it represents the Savanna 

 Sparrow of the mainland. 



Not only new species but new habits may arise on is- 

 lands. Environment is the mold in which habit is cast, and 

 such variations in the mold as may readily occur on islands 

 are quickly reflected in its product. The nest-building' habits 

 of the Ospreys on Gardiner's Island, and of the Pelicans on 

 Pelican Island, are cases in point. 



Of the two islands whose bird-life is sketched beyond, 

 one is comparatively large with diversified topography and 

 flora and correspondingly rich avifauna ; the other is small 

 and composed of only beach and marsh, but both show the 

 preserving powers of insular life, by the presence on them 

 of birds which have virtually ceased to breed in the adjoin- 

 ing regions. 



