BIRD CHARACTERISTICS 
109 
The beaks of birds show great variation and adaptation 
for defense and food-getting. Hawks, owls, and eagles 
have the upper jaw curved over, hooked, and adapted for 
tearing their food; herons and bitterns have the beak modi¬ 
fied into a long, pointed weapon of offense and defense; 
grosbeaks (gros'beks) and finches have a short, stout beak 
for crushing seeds and other hard foods; while humming 
birds have a long, slender 
beak which in some kinds 
is curved so that they 
may reach the bottom of 
certain flowers. Study 
Figures 94, 99, 107, 109. 
The birds show a num¬ 
ber of other interesting 
adaptations which are of 
use to them. These are 
hollow bones, a keeled 
sternum (breastbone),and 
a high body tempera¬ 
ture. 
The skeleton of a bird 
shows a prominent ridge 
on the breastbone. This 
is the keel of the ster¬ 
num, which serves as a 
place of attachment for 
the large wing muscles 
(Figure 98). The lungs of the bird are small, but air tubes 
extend into the bones, so that the body of the bird is 
relatively lighter than that of animals with solid bones. 
Birds lead an active life, which means that they use a 
great deal of energy. This energy comes from the oxidation 
going on in the body. In birds, oxidation is more rapid than 
in other vertebrates, owing to the fact that they almost 
