Tarsi shorter than middle toe … Dendrochelidon.
The Swifts are cosmopolite, occurring throughout the globe. All the genera enumerated above are well represented in the New World, except the last two, which are exclusively East Indian and Polynesian. Species of Collocallia make the “edible bird’s-nests” which are so much sought after in China and Japan. These are constructed entirely out of the hardened saliva of the bird, although formerly supposed to be made of some kind of sea-weed. All the Cypselidæ have the salivary glands highly developed, and use the secretion to cement together the twigs or other substances of which the nest is constructed, as well as to attach this to its support. The eggs are always white.
There are many interesting peculiarities connected with the modification of the Cypselidæ, some of which may be briefly adverted to. Those of our common Chimney Swallow will be referred to in the proper place. Panyptila sancti-hieronymæ of Guatemala attaches a tube some feet in length to the under side of an overhanging rock, constructed of the pappus or seed-down of plants, caught flying in the air. Entrance to this is from below, and the eggs are laid on a kind of shelf near the top. Chætura poliura of Brazil again makes a very similar tube-nest (more contracted below) out of the seeds of Trixis divaricata, suspends it to a horizontal branch, and covers
the outside with feathers of various colors. As there is no shelf to receive the eggs, it is believed that these are cemented against the sides of the tube, and brooded on by the bird while in an upright position. Dendrochelidon klecho, of Java, etc., builds a narrow flat platform on a horizontal branch, of feathers, moss, etc., cemented together, and lays in it a single egg. The nest is so small that the bird sits on the branch and covers the egg with the end of her belly.
Owing to the almost incredible rapidity in flight of the Swifts, and the great height in the air at which they usually keep themselves, the North American species are, of all our land birds, the most difficult to procure, only flying sufficiently near the surface of the ground to be reached by a gun in damp weather, and then requiring great skill to shoot them. Their nests, too, are generally situated in inaccessible places, usually high perpendicular or overhanging mountain-cliffs. Although our four species are sufficiently abundant, and are frequently seen in flocks of thousands, it is only the common Chimney Swift that is to be met with at all regularly in museums.
Subfamily CYPSELINÆ.
The essential character of this subfamily, as stated already, is to be found in the feathered tarsus; the reduction of the normal number of phalanges in the middle toe from 4 to 3, and of the outer toe from 5 to 3, as well as in the anterior or lateral position of the hind toe, not posterior. Of the two genera assigned to it by Dr. Sclater, one, Cypselus, is enlarged by him so as to include the small West Indian Palm Swifts, Tachornis of Gosse.
Genus PANYPTILA, Cabanis.
Panyptila, Cabanis, Wiegm. Archiv, 1847, I, 345.—Burmeister, Thiere Bras. Vögel, I, 1856, 368. (Type, Hirundo cayanensis, Gm.)
Pseudoprocne, Streubel, Isis, 1848, 357. (Same type.)