42 USEFUL BIRDS. 
fluids ; the chyle is drawn off by the lacteals, and the residue 
is excreted. The vigor, perfection, and rapidity of these 
processes in insect-eating birds are such as might be expected 
among animals of such high temperature, perfect respiration, 
and rapid circulation. 
The various dilations of the digestive tract serve well their 
purpose of enabling the bird to consume the large amount 
of food necessary for its maintenance. Digestion is partic- 
ularly rapid in the growing young of most birds, for they 
require not only food sufficient to sustain life, but an extra 
supply as well to enable them to increase daily in size, and 
to grow, in a few days, those wonderful appendages that we 
call feathers. 
The Growth of Young Birds. 
The growth of many birds from the egg to the hour of 
flight requires less time than is needed by some insects to 
reach the flight stage. It is most significant that young birds 
can develop as rapidly as can many in- 
sects on which they feed, for it shows how 
readily, under favorable conditions, the 
increase of birds might keep proportion- 
ate pace with that of insects. Weed and 
= = Dearborn, in their interesting manual, en- 
cat be ae titled “Birds in their Relations to Man,” 
naked, blind,andhelp- state that they watched four young Song 
less, with mouth open 
for food. Reduced; Sparrows that were out of the nest on the 
cee eighth day. Mr. Owen records another 
instance where a brood of young Song Sparrows were 
fledged and left the nest within the same period.!_ Probably 
this is exceptional; but many of the smaller birds rear their 
young from the egg to the first flight within two or three 
weeks. Mr. Owen found that on one particular day this 
family of five young Song Sparrows increased in average 
weight forty-eight per cent., while the smallest bird gained 
fifty-five per cent. in a single day. 
The young of perching birds (Insessores) come into the 
world tiny creatures, either naked or covered with down, 
* A Family of Nestlings, by D. E. Owen. The Auk, Vol. XVI, No. 3, July, 
1899, pp. 221-295. 
