35 
DESCRIPTIVE ORNITHOLOGY 
CLASS— AVES. BIRDS 
Birds, as a class, may 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, 
page 24), but examination shows that they are not true teeth. 
SUBCLASS— CARINATAE. KEEL-BREASTED BIRDS 
Present day, toothless birds are divided into two subclasses, Ratitae 
or raft-breasted birds and Carinatae or keel-breasted birds. The Ratitae 
include the Ostriches and Emus which are without a keel to the breast bone for 
the attachment of wing muscles and are flightless. There is 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 Carinatae ) are divided into numerous 
orders which are considered here in the sequence adopted by the American 
Ornithologists’ Union. 1 
Order — Pygopodes. Diving Birds 
General Description. The Divers, a rather heterogeneous order, 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, page 23), and the toes are either partly (Figure 13, page 25) 
or completely (Figures 2 and 6, pages 23 and 24) webbed. The wings are small in com- 
parison with the size of the body. The bill is straight and usually tapered, moderately 
long, but occasionally flattened and deepened, as in the cases of the Auks and Puffins; 
in the 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 
crevices and holes in the ground. 
In consequence of the peculiar leg construction, an unusually upright 
carriage of body is necessitated when on land, and the birds walk with diffi- 
culty. 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 proportion to 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. 
Economic Status. The Diving Birds feed almost entirely upon aquatic 
life, usually captured by diving and pursuit under water. Economically, they 
are of slight importance. The Canadian representatives of this order at 
present recognized in American Check-list are divided into three families: 
the Grebes, Colymbidae; the Loons, Gaviidae; the Auks, Murres, etc., Alcidae, 
i Check-list of North American Birds. 
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