98 FRIENDS WORTH KNOWING. 
ence of altitude accomplishing the same climatic results as 
a change in latitude. 
We can see various causes of these migrations, some of 
** ONLY A OAT-BIRD.”’ 
which have already been suggested, but the chief cause 
seems to be the necessity of their accustomed food. We 
find that those birds which make the longest and most com- 
plete migrations are insect and honey-eaters; while the 
graminivorous and omnivorous birds, and such, like the tit- 
mouse and nut-hatch, as subsist on the young of insects to 
be found under the bark of trees, go but a short distance to 
escape inclement weather, or do not migrate at all. Sports- 
