or less, in proportion to its weight, than an animal that lives on the ground? Are the vocal cords of a bird higher or lower in the windpipe than those of a man? (Fig. 307.)
The heart of a bird, like a man's heart, has four chambers; hence it keeps the purified blood separate from the impure blood. Since pure blood reaches the organs of a bird, oxidation is more perfect than in the body of any animals yet studied. Birds have higher temperature than any other class of animals whatsoever. Tell how the jaws, tail, and wings of the fossil bird Archæopteryx differed from living birds (Fig. 290).
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Fig. 307.—Position of Vocal Cords (str) of Mammal and Bird.
Question: Does a fowl ever croak after its head and part of its neck are cut off? Explain.
Suggestions.—In the field work, besides seeking the answers to
definite questions, pupils may be required to hand in a record of the
places and times of seeing a certain number of birds (20 to 40), with
the actions and features which made each distinguishable. Also, and
more important, each pupil should hand in a record of a careful and
thorough outdoor study of one common species (see below) as regards
habits, nesting, relation to environment, etc.
Field Study of a Common Species.—(For written report.) Name of species. Haunts. Method of locomotion when not flying. Flying (rate, sailing, accompanying sound if any, soaring).
What is the food? How obtained? Association with birds of its own species. Relation to birds of other species.
Where does it build its nest? Why is such a situation selected? Of what is the nest built? How is the material carried, and how built into the nest? Does the bird's body fill the nest?
Describe the eggs. Does the male bird ever sit or otherwise assist female before hatching? Does it assist after hatching?
