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, the tail, and the wings of the fossil bird Archæopteryx differed from living birds (Fig. 290). 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 the times of seeing a certain number of birds (20–40) 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? How long is taken to lay a sitting of eggs? How long before the birds are hatched? _When hatched_ are they helpless? Blind? Feathered? (Figs. 301, 302.) Do the nestlings require much food? How many times in an hour is food brought? How distributed? Even if the old birds sometimes eat fruit do they take fruit to the young? What do they feed to the young? How long before they leave the nest? Do the parents try to teach them to fly? Do the parents care for them after the nest is left? What songs or calls has the bird? [Illustration: FIG. 308.—EUROPEAN TOMTIT’S NEST. What are the advantages of its shape? ] [Illustration: FIG. 309.—TAILOR BIRD’S NEST (India). Instinct for nest building highly perfected. ] =General Field Study.=—(_For written report._) Name the best and poorest flyers you know; birds that fly most of the time; birds that seldom fly. Observe birds that pair; live in flocks. Does their sociability vary with the season? Do you ever see birds quarrelling? Fighting? What birds do you observe whipping or driving birds larger than themselves? Which parent do young birds most resemble? Name the purposes for which birds sing. Which senses are very acute? Why? Dull? Why? Can you test your statements by experiment? A partridge usually sits with 18 to 24 eggs in nest. About how long after laying first egg before sitting begins? Do several partridge hens lay in the same nest? [Illustration: