2 BIRDS OF EASTERN NORTH AMERICA. 



largest Ustricli, which, it is chiinu'il, was still in existeuco at the beginning of the 

 present eentniy, and a few of the older natives claim to have heard their fathers talk 

 of seeing it alive. We know of several species which have become extinct dnring the 

 l»ast fifty years, notably the Great Auk and the Labrador Duck, Camptohemits lahra- 

 (lorins. 



ill the West Indies we have numerous instances of the recent disappearance of 

 insular forms. The .lamiuca Petrel, Aestrelaia cunb(ea, is now supposed to have been 

 exterminated by the Mongoose {Herpestes), which animal was introduced into the 

 island some years ago for the purpose of killing the rats. AVallaee, in his -'Distri- 

 bution of Animals." states that no less than six species of Parrots were said to have 

 been formerly found in (iuadaloupe and Maitinicpie, but at the present time no Parrots 

 are known to exist on either of those islands. 



Ledru, in his " Voyage aux iles Teneritfe," published in Paris, in ISIO, men- 

 tions several birds which are now unknown, among them a green pigeon from 8t. 

 Thomas. 



While many species have become extinct, others have extended their range, and, 

 accommodating themselves to changed conditions and environment, have in the course 

 of time developed new forms. Birds showing decided and constant differences are 

 recoiiuized as aj^ecies, whereas if the differences in color or size are not very gfeat and 

 intermediate forms occur showing an intergi-adation from one to the other, they are 

 called races or fii(I)Sj)ecles. Races are really species in process of development and 

 are caused by difference in climate, food, etc. Insular forms which are sutficiently 

 removed from the [)arent stock to warrant the belief that their isolation is complete, 

 are generally recognized as species even though the differences would hardly be worthy 

 of specific recognition if the two forms occurred in close i)roximity on the main land. 

 It should be borne in mind, however, that the line of deinarkatiou between a species 

 and a suljspecies is a purely arbitrary one and is largely a matter of individual opinion. 

 Subspecies are distinguished by a third name; for example, Dendroica palmnrnm 

 }n/l)Oi-lrr!/s('<i is a race or subspecies of Dendroiai, jialiiiarHni. 



Haviii'j; learned something as to what a bird is, let us take up in order the more 

 iuiixntaiit external iiarts, such lus the wing, tail, bill, and feet. 



