562 The Roller-like Birds 



Swallows, with which, indeed, they were placed by the early writers. They have 

 the same general form and much the same habits of life, but anatomy teaches 

 us that the resemblance is merely superficial, and that no real relationship 

 exists between them. Without unduly anticipating, it may be mentioned that 

 the Swallows have invariably twelve tail-feathers as against ten in the Swifts, 

 and a very different vocal apparatus, since they belong to the so-called singing 

 birds, though it must be confessed that their powers of song, with a few ex- 

 ceptions, hardly exceed those of the present group. 



To further particularize, the Swifts are small, preeminently aerial birds, with 

 very long, pointed wings in which there are ten primaries and always less than 

 nine secondaries. The bones of the wings are naturally peculiar, there being 

 a very short humerus, a longer forearm, and an extremely long hand, while the 

 tarsi are extremely short and the feet weak, since they very rarely alight upon 

 the ground or perch, except at night. The skull and breast-bone are very char- 

 acteristic, the former being broad and flat, with the mouth split to beneath the 

 eyes, the bill being short, broad at base, and somewhat curved, thus giving 

 a very wide gape. The palate is of the segithognathous type, and the basip- 

 terygoid processes of the base of the skull are absent. The breast-bone may be 

 known by its very high keel and unnotched front margin. A further peculiarity 

 of the foot is worthy of mention. In the true Swifts (Micro pod ina) the middle 

 and outer toes possess only three joints, and all four toes are directed forward, 

 while in the other groups the toes are normal as regards the number of joints and 

 the hind toe is directed backward, or is at least reversible, that is, may be turned 

 either way. The plumage, which is moulted but once annually, possesses a small 

 or moderately large aftershaft, and the naked tracts are provided in the adults 

 with a blackish down ; the young when hatched are naked, blind, and helpless. 



About one hundred species and subspecies of Swifts are known, and like their 

 analogues, the Swallows, they are practically cosmopolitan, being found through 

 the entire world except at the extreme north and south, where^the supply of 

 insect food necessary to their existence is not forthcoming. They are in general 

 dusky, greenish black, or mouse-brown birds, though this unpretentious colora- 

 tion is not infrequently relieved by a white chin, throat, or rump. Their chief 

 charm lies in their marvelous power of flight, being perhaps unsurpassed in 

 this respect by any other birds. The flight is accomplished by two or three 

 rapid beats of the wings, succeeded by a gliding movement, and like a flash they 

 go, now skimming the surface of land or water, now wheeling and circling aloft 

 with the lightness of down, or vanishing to mere specks in the sky. Not only is 

 the flight swift and powerful, but it can be sustained almost indefinitely and 

 without apparent effort. Hundreds of miles are often covered during the hours 

 of daylight in their passing between nesting site and feeding ground. While 

 they are not exactly gregarious, many are often seen in company, and most of the 

 species nest in colonies often of vast size. They are completely insectivorous, 

 capturing all of their food on the wing. Their nests are among the curiosities of 

 bird architecture : some are composed entirely of saliva secreted by the birds 

 themselves, as will be described later; others are made of fragments of bark, 



