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 aérial birds and, so far as known, are 
the only ones among all birds 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 against the side of vertical surfaces, as a rock or 
the inside of a hollow tree trunk or a chimney, pressing the tail 
against 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 (Hirundinide) the Swifts are insectivorous 
and take their prey while flying; but their manner of flight is differ- 
ent, as might be expected from the very different structure of their 
wings. In this respect, however, there is much difference between 
different 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 Chextura) is much less rapid and more flut- 
tering. 
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 Che- 
turine) 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 (Chetura 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-hieronymi, 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. Chetura brachyura is said to make 
@The Tree Swifts (Dendrochelidonide), however, are said to perch upon trees 
in the manner of Swallows and other birds. 
b See Richmond, Auk, xv, 1898, 7-10, pl. 1. 
