22 INTRODUCTION. 



Aves, or birds, form a class of the Animal Kingdom, and 

 have, in their classification, been primarily divided by eminent 

 ornithologists into three subclasses (lately dispensed with, 

 however, in " North American Birds") : Aves Aerece or In- 

 sessores (aerial birds or "perchers"), Aves Terrestres or 

 Cursores (terrestrial birds or " runners "), and Aves Aqua- 

 ticce or Natatores (aquatic birds or " swimmers "). The gen- 

 eral rule of division is this : hind toe 17 on a level with the 

 other toes, " perchers " ; hind toe not insistent 17 and feet not 

 f ully webbed, " runners " ; hind toe elevated, 17 but feet fully 

 webbed, " swimmers." This rule is applicable only to typical 

 forms, with which other forms are ranked through evident 

 affinity. It is to be remarked that, in a great measure, aes- 

 thetic or intuitive perception is the best means of determining 

 position. By modern classification birds are arranged on the 

 descending method, by which the highest and most refined 

 types occupy the highest position.* Thus, the Cursores in- 

 clude those birds who scratch for their food (Turkeys, Grouse, 

 etc.), and the waders (such as Snipe, Plover, Herons, Rails, 

 etc.). These two suborders (Gallince and Grallatores) rep- 

 resent 18 (in the approximate proportion of one to four) about 

 two elevenths of North American birds. The Natatores 

 include various sea-birds, the Swans, Geese, Ducks, Terns, 

 Gulls, Pelicans, Petrels, and Cormorants, and form about one 

 fourth of our fauna. The Insessores include all the typical 

 land-birds, 377 of the 635 North American species admitted 

 in Dr. Coues's check-list, and more than one half of about 

 300 species known to have occurred in Massachusetts. In 

 this volume I have, with the exception of the game-birds, 

 treated the typical land-birds only. The Insessores contain 

 five orders, described in the following chapters. 



17 In certain cases wanting, or appar- writers on North American birds, be- 



ently wanting. gins with the lowest and most general- 



* This order was reversed in 1886 ized forms, the Grebes, and ends with 



by the Committee on Classification and the highest and most specialized, the 



Nomenclature of the American Orni- Thrushes and Bluebirds. W. B. 



thologists' Union, whose check-list, llj In number of species (according to 



now almost universally followed by Coues's list). 



