41 



DESCRIPTIVE ORNITHOLOGY. 



CLASS AVES. BIRDS. 



Birds, as a class, can be divided into toothed and toothless birds, 

 although the former are now extinct and are known only by their frag- 

 mentary remains preserved as fossils. All modern birds are toothless. 

 Some species, for example the Mergansers, are furnished with serrations 

 in the horny bill that have a superficial resemblance to teeth (Figure 7, p. 

 19), but examination shows that they are not true teeth. 



SUBCLASS CARINAT.E. KEEL-BREASTED BIRDS. 



Present day, toothless birds are divided into two subclasses, Ratitce or 

 raft-breasted birds and Carinatce or keel-breasted birds. The Ratitce 

 include the Ostriches and Emus which are without a keel to the breast 

 bone for the attachment of wing muscles and are flightless. There are none 

 in North America and they are, therefore, not dealt with here. The term 

 keel-breasted is derived from the high, thin, keel-like projection from the 

 middle of the breast bone, to which the powerful breast or wing muscles 

 are attached. 



Keel-breasted birds (subclass Carinatce) are divided into numerous 

 orders which are considered here in the sequence adopted by the American 

 Ornithologists' Union. 



Order Pygopodes. Diving Birds. 



General Description. The Divers, as their name implies, are birds fitted for sub- 

 aquatic pursuits. The hip joint is set far back on the body and the leg mechanism is 

 better fitted for swimming than for walking. The tarsus, the visible part of the leg, is 

 much flattened (Figure 2, p. 18), and the toes are either partly (Figure 13, p. 20) or 



latter species this specialization reaches its highest development in the order. 



Distinctions. Toes, three or four entirely or partly webbed, tarsus flattened, tail 

 inconspicuous or small. 



Field Marks. Small wings and tail; and straight, narrow bills not duck-like The 

 Divers bear a superficial resemblance to Ducks, but where Ducks would fly the Divers 

 dive. 



Nesting. In the immediate vicinity of water on reedy shores or rocky ledges, or in 

 crevices and holes in the ground. 



In consequence of the peculiar leg construction, an unusually upright 

 carriage of the body is necessitated when on land, and they walk with 

 difficulty. Indeed some species are almost helpless on the ground and are 

 unable to rise into the air except from the water, off steeply rising ground, 

 or against a strong head wind. They swim and dive with ease and, though 

 their wings are small in comparison with the size of the body, when once on 

 the wing they fly with rapid beats, swiftly and strongly, in straight lines 

 or long curves without evolution or manoeuvring. 



