AVES 309 



but it does not lack much of equaling the body in bulk; and the ob- 

 server will most hkely make the remark that such an enormous bill 

 must be very heavy. The fact is, however, that the bill is extremely 

 light in comparison with its size, being very thin and filled with hght, 

 cellular bony tissue." It is not clear of what value such an enormous 

 bill can be to the bird, for none of its activities appear to be connected 

 with this great structure. In all probabhty this great bill is an ex- 

 ample of an overspecialized structure, much like the enormous horns 

 of the extinct Irish elk, which are believed to have finally caused the 

 extinction of the species. 



The woodpeckers and sapsuckers are among the most familiar 

 of our native birds, and they are especially known for their habit of 

 riddling the bark and wood of trees in their search for insects and 

 larvae, and for their noisy drumming while engaged in this task. The 

 finest of the woodpeckers is the great ivory billed woodpecker, which 

 has a length of about twenty inches. 



The Passerine Birds (Passeriformes) 



This order, consisting largely of perching birds, is for the Neornithes 

 what the order Acanthopterygii is for the Teleostomi; the largest, 

 most varied, most distinctively modern order of the sub-class. Over 

 five thousand species, or nearly half of all known species of birds, are 

 included within this single order. The hst of families, thirty-six in 

 number, is too long to recite, but the reader may get an idea of the 

 scope and variety of the order from the following list of representative 

 types: — broad-bills, wagtails, rock-wrens, king-birds, oven-birds, ant- 

 birds, lyre-birds, larks, pipits, fork-tails, thrushes, robins, warblers, 

 gnatcatchers, mocking-birds, water-ousels, wrens, tits, swallows (Fig. 

 159, A), martins, wax- wings, shrikes, nut-hatches, greenlets, titmice, 

 orioles (Fig. 159, D), birds of paradise, crows, ravens, magpies, 

 stariings, honey-eaters, sun-birds, flower-pickers, creepers, quit-quits, 

 tanagers, weaver-birds, finches, stariings, buntings, etc. 



In general, it may be said that the passerine birds are of small or 

 moderate size, of conservative or generalized proportions, and without 

 exaggerations of bill or feet. Some of them, however, have developed 

 a wealth of plumage elaborations, which is taken to be one of the 

 criteria of racial senescence. Garrod and Forbes subdivide the pas- 

 serine birds into two sub-orders: the Desmodadyli, in which the hallux 

 or hind toe is weak and the front toes are more or less united; and the 



