230 FRIENDS WORTH KNOWING. 
sometimes, in defect of hair, lining the interior with a mixt- 
ure of slender strips of smooth vine bark, and rarely with 
a few feathers; the whole being of a considerable thick- 
ness and more or less attached to the external pouch. Over 
the top the leaves,as they grow out, form a verdant and 
agreeable canopy, defending the young from the sun and 
rain. There is sometimes a considerable difference in the 
manufacture of these nests, as well as in the materials 
which enter into their composition. Both sexes seem to 
be equally adepts at this sort of labor; and I have seen the 
female alone perform the whole without any assistance, 
and the male also complete this laborious task nearly with- 
out the aid of his consort, who, however, in general, is the 
principal worker.” 
Many persons believe that there is a constant tendency 
in birds to vary their architecture to suit their surround- 
ings, in accordance with climate, greater or less readiness of 
certain materials, and security. The Baltimore oriole af- 
fords a good illustration of this tendency. Like the swal- 
lows, robin, bluebird, pewit, and others, the oriole has aban- 
doned the wilds for the proximity to man’s settlements, do- 
ing it chiefly for two reasons—the greater abundance of 
insect food, and protection from hawks, owls, and crows, 
which are fewer in number and less bold in the clearings. 
