12 GENERAL HISTORY OF BIRDS. 



location. Those borne on the hand are called primaries; those on the fore-" 

 arm, secondaries; and those above the elbow, tertiariesJ The primaries are 

 remarkably constant in number, the great majority of birds having 10; some 

 birds have an additional very small outer primary, but no living bird has 

 more that 1 1 ; many of the higher passerine birds have the tenth or outermost 

 primary very small, and in the Finches, Swallows, American Warblers and 

 several other families, only 9 primaries occur. The relative length of the 

 primaries, and the width and texture of the vanes, are useful characters in 

 separating genera and species. The secondaries are shorter than the primaries 

 and their number is much more variable; the smaller Swifts and Humming 

 Bird have only 6, while Albatrosses have 40 or more. The tertiaries are seldom 

 noticeably developed, and are of little importance. The coverts of the remiges 

 are called the ujjper and under wing coverts, according to their position, and 

 are also sub-divided as major and minor coverts according to their size and 

 importance. The under wing-coverts, near the sides of the body, are often 

 conspicuous for their size and color, and are known as axiUaries. They are 

 especially notable in Snipes and Plovers. The small group of feathers borne on 

 the thumb is called the alula; the number of feathers in it ranging from 2 to 

 6. The rectrices are borne on the compound "ploughshare-bone", ov pygostyle, 

 which terminates the vertebral column. Their number is variable, though the 

 great majority of birds have 12. The Anis have only 8, Cuckoos, Humming 

 Birds and many others have 10, while many game birds have from 14 to 22, 

 and some water-birds even more than that; the Penguins have 32 or more. 

 The relative lengths of the rectrices and their individual and collective form 

 are important characters. The coverts, known as upper and. under tail coverts, 

 are sometimes longer than the rectrices, and one or more pairs may assume 

 the function of the latter. 



Many birds have special crests, knots, tufts, or groups of feathers, which 

 are notable either for their greater size, or more conspicuous coloring. Such 

 groups usually form special tracts in the pterylosis, and are almost invaria- 

 bly composed of highly specialized contour-feathers. They may be a perma- 

 nent part of the plumage, or only assumed during the breeding season, and 

 they are usually much more noticeable in the males. Indeed, they are often 

 wholly wanting in the females, as the plumage of the weaker sex is, in the 

 majority of birds, much plainer than that of the males. These specialized 

 groups of feathers are generally found on the top or back of the head, on the 

 shoulders, or on the rump, but they may appear on any part of the body. 

 The upper tail coverts, the upper wing coverts, and the occipital contour- 

 feathers are the ones most often concerned. Marked differences in the appear- 

 ance of the plumage may be caused not only by these special groups of feathers, 

 but also by the absence of feathers on certain parts of the bird where they are 



