AN ORNITHOLOGICAL LECTURE. 97 
there are many exceptions to this rule, for with not a few 
birds the males and females travel together; and with some, 
old and fully plumaged males are the last to arrive. All 
birds migrate more or less—even such, like the crow and 
song -sparrow, as stay with us through the year; for we 
probably do not see the same individuals both winter and 
summer. Even tropical birds move a little way from the 
equator, and back again with the season; and in monntain- 
ous regions most of the birds, and many small quadrupeds, 
THE HUMMING-BIRD’S NEST, 
have a vertical migration only, descending to the valleys in 
winter, and reascending to the summits in summer-—differ- 
t 
