212 AVES. 



Class II. — AVES. (The Birds.) 



A Bird may be defined as an air-breatliing vertebrate with a 

 covering of feathers ; warm blood ; a complete double circulation ; 

 the two anterior limbs (wings) adajjted for Hying or swimming, the 

 two j)Osterior limbs (legs) adapted for walking or swimming; respi- 

 ration never effeited by gills or branchiu', but, after leaving the egg, 

 by lungs, which are connected with air cavities in various j)arts of 

 the body. lu'])rodMclion by eggs, which are fertilized within the 

 body and hatched externally, either by incubation or exposure to 

 the heat of the sun ; the shell calcareous, hard and brittle. 



Much more might be added, but the obvious character is this : 

 All Birds have feathers, and no other animal has feathers, or, as 

 Stejneger puts it, " A bird is known by its feathers." There is 

 probably no other character of importance which distinguishes 

 birds living and extinct as a whole, from the Reptilia. 



The classification of this group, as of most others, is still in an 

 unsettled condition. Strictly speaking, the existing members of 

 the class are .so closely related that they might, with j)ropriety. bo 

 combined into one order, wliich, by Professor Gill, has been named 

 EuKHii'iDi'K.K. At present, however, the term "order" may be 

 applied to the groups so designated below, without thereby imply- 

 ing any structural diffi-rences such as separate the " orders " of 

 Keptiles or even of Fishes. The Eurhipidurce are made a sub- 

 class by Stejneger, while Coues divides them into two "sub-classes," 

 the llalilic (f)striches, etc.), and the Carinnlrr. To the Carinatcr, 

 characterized by the keeled sternum and more or less developed 

 wings, all American birds belong. (Lat., avis, bird.) 



The " orders " of the Carinati^ l?irds, as now adopted, are rather 

 temj)orary, pending invest igaticm of certain groups. Tliey an- also 

 in a degree conventional, .some of them being admittedly unnatural 

 in tlu'ir com])osition, while none of them rej)resent any such struc- 

 tural liilTercnci's or differences of such long standing in time as 

 those which characterize the orders of Mammals or Ueptiles. or most 

 of the orders of Kisiies. For reasons which have U-en elsewhere 

 piven, I follow in tliis work without ex<'eption the classiricalion, 

 8e(|uence, and nomenclature adopted by the American Ornitholo- 

 gists' Union. A system in some respects more in accord with 



