White-throated Swift 251 
and other vegetable matter and a few feathers, all glued 
together with hardened saliva. The eggs, four or five, 
are white and measure °87 x ‘52. 
A female shot by Drew, June 20th, at 13,000 feet near 
Silverton, contained an egg ready for extrusion; while 
Gale, though he apparently never actually took eggs 
of this species, gives May 25th to June 10th as the date 
for fresh eggs in Boulder co. 
Family TROCHILIDA. 
The Humming-birds which make up this family hardly 
require a diagnosis ; their tiny size and their metallic 
colouring at once distinguish them. The bill is very 
long and slender and usually straight, the nostrils are 
linear and protected by an overhanging scale or oper- 
culum, and often feathered and concealed ; the wing is 
long and consists of ten elongated and often curiously 
attenuated primaries, and six reduced and very short 
secondaries ; the tail consists of ten rectrices ; the feet 
are extremely small and weak, and only adapted to 
perching. 
THE FOLLOWING KEY SEPARATES THE SPECIES FOUND IN COLORADO, 
A. Tail not white-tipped (males). 
a. Back chiefly rufous, gorget coppery-red. S. rufus, ¢ p. 255. 
b. Back and central tail-feathers green. 
a1 Tail rufous at the base, gorget crimson. 
S. platycercus, gp. 253. 
b! Tail without rufous; gorget dusky purplish. 
A. alexandri, 3 p. 252. 
c. Back green, central tail-feathers dusky. S. calliope, ¢ p. 256. 
B. Tail white-tipped (females), 
a. No visible rufous at the base of the tail. 
a! Tail-feathers obtusely pointed ; no rufous on the flanks. 
A. alexandri, 2 p. 252. 
bt Tail-feathers spoon-shaped and rounded, flanks slightly 
washed with rufous, S. calliope, 2 p. 256. 
