684 BULLETIN 50, UNITED STATES NATIONAL MUSEUM. 



as inner toe), directed inward, more or less versatile or capable of 

 being directed forward, the inner toe also more or less versatile, or 

 capable of being directed backward. 



The Swifts are eminently aerial birds and, so far as known, are 

 the only ones among all bu'ds of flight which do not perch upon the 

 branches of trees — a remarkable characteristic when their similarity 

 in general habits in other respects to the Swallow is considered. 

 They cling easily agamst the side of vertical surfaces, as a rock or 

 the inside of a hollow tree trunk or a chimney, pressing the tail 

 agamst the surface as an additional support (as in the case of wood- 

 peckers), but apparently they are not able to grasp a branch with 

 their feet in such a way as to maintain a fixed position thereon.'* 



Like the Swallows (Hirundinidse) the Swifts are insectivorous 

 and take their prey while flying; but their manner of flight is dift'er- 

 ent, as might be expected from the very dift'erent structure of their 

 wings. In this respect, however, there is much difference between 

 dift'erent genera, the flight of some being characterized by a velocity 

 perhaps unequaled among other birds, while that of others (as for 

 example the species of CTisetura) is much less rapid and more flut- 

 termg. 



There are many interesting peculiarities connected with the nidi- 

 fication of Swifts, some of which may be briefly described. In this 

 connection it may be mentioned that the salivary glands are often 

 highly developed, and the glutinous or mucilaginous substance which 

 they secrete enters more or less into the composition of the nest. 

 In the oriental genus Collocalia (belonging to the subfamily Chre- 

 turinae) the nest is sometimes composed entirely of this substance, 

 and constitutes an important delicacy among Chinese and Japanese 

 epicures. The nest of the common Chimney Swift {Clixtura pelagica) 

 of the eastern United States and related species of the same genus 

 is of similar form to that of the ''edible birds' nests" above men- 

 tioned, but is composed of dead twigs glued together by the saliva. 

 The beautiful large black and white swift of Guatemala, Panyptila 

 sancti-liieronymi, attaches to the under side of an overhanging rock 

 a tube some feet in length, constructed of the pappus or seed-down 

 of plants, caught flying in the air. Entrance to this is from the 

 lower end, and the eggs are laid on a kind of shelf near the top. A 

 smaller but otherwise similar species (P. cayanensis) found from 

 Nicaragua southward attaches a similar nest to the under side of 

 a large branch of a forest tree.^ Chsetura hrachyura is said to make 



a The Tree Swifts (Dendrochelidonidse), however, are said to perch upon trees 

 in the manner of Swallows and other birds. 

 b See Richmond, Auk, xv, 1898, 7-10, pi. 1. 



