XXV. BIRDS

THE following questions may be worked out during a visit to a zoölogical park or during a field trip.1

Pick out some particular bird for your study and take notes upon the following series of questions. Do not expect to be able to answer all the questions which follow.

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Protection. - Does the bird rest or nest in trees, bushes, or grass? general, what are the colors of the bird? Do they harmonize with the surroundings when the bird is at rest? Look especially for birds on the nest. Often such birds will remain quiet, allowing the observer almost to touch

them before they attempt to fly away. In some cases the light, glinting through the trees, gives a mottled or banded appearance to the leaves, somewhat resembling the same kind of markings on a bird.

Try

Flight. Watch a bird in flight. to determine the exact changes in the position of the wings that take place. The tip of the wing usually describes a curve which results in the forming of the figure. Notice that the rate of movement of the wing differs greatly in different birds. Birds with long, thin wings, as the hawks and gulls, move the wing in flight with much less rapidity than those with short, wide wings, as the grouse or quail. The latter birds start with much less apparent effort than the birds with longer wings; they are, however, less capable of sustained flight.

The wing of a bird is slightly concave on the lower surface when outstretched. Thus on the downward stroke of the wing more resistance is offered to the air.

Under the covering of feathers the parts of the wing may be made out. This may easily be done from a fowl at home, or dead sparrows may be used in the laboratory. Find and identify the parts corresponding to the human arm, forearm, and hand. The last division of the wing is homologous to our

1 Bird activities may best be studied out of doors. Any city park offers more or less opportunity for such study, for seyeral of our native birds make the parks their home. If not these, then the English sparrow can be found anywhere in the East. The best time for making observations is early in the morning, especially in the Spring season.

hand and wrist, the third and fourth fingers are absent while the wrist bones and fingers of the fowl have grown together, thus giving greater strength and support. This is evidently an adaptation for flight.

Feathers. Few people realize that the body of a bird is not completely covered with feathers. Look for featherless areas on the body of the bird you are working with. Notice that feathers are of several shapes. Soft down feathers cover the body, serving for bodily warmth. In the wings we find quill feathers; these are adapted for service in flight. Let us examine a single quill feather more closely. The main axis of the feather, called the shaft, is hollow, light, and strong. From the shaft, lateral branches, called barbs, are given off. The barbs give rise to still smaller lateral structures, the barbules, the latter just visible to the naked eye. Each barbule is interlocked with its neighbor by means of many microscopic hooks, the barbicels. If you attempt to pull apart the barbs of a feather, you will find that they stick together. What is the reason for this? Might this arrangement be of use in flight, and if so, how?

Draw a quill feather and show all the parts visible to the naked eye.

Feathers. Feathers are developed from the under layer of the skin. At first they appear to be tiny, pimplelike projections. They are formed in almost exactly the same manner as are the scales of a fish or a lizard. The first feathers developed on the body are evidently for protection against cold and wet. In aquatic birds the feathers are oiled constantly, and thus shed water. The feathers of some male birds are brightly colored. This seems to make them attractive to the females of the species; thus the male wins its mate.

Perching. The habit of perching is an interesting one. In many perching birds the tendons of the leg and foot, which regulate the toes, are self locking; thus while asleep such birds balance themselves perfectly. A certain part of the ear, known as the semicircular anals, has to do with the function of balancing. In the flamingoes, which do not perch, balancing appears to be automatic and elf-regulating; thus the bird is able to go to sleep when in an upright position.

Tail. The tail is sometimes used in balancing; its chief function, however, appears to be that of a rudder during flight. Note that the tail is merely a small protuberance of the body, the feathers which grow there give it the shape. In most birds, under the skin of the tail is located a large oil gland, whence comes the supply of oil that is used in waterproofing the feathers.

Adaptation in the Lower Limbs. - In the leg identify the thigh, the shin, and foot. The ankle of the bird is extremely long, the seven bones found

in man are here in part lost and partly grown together. Scales are found on the ankle and foot; in very early life they resemble feathers, both in appearance and manner of growth. If mounted specimens are obtainable, notice the different feet in different birds. Some have the foot adapted to perching, others for swimming, others wading, etc. Take some one example and attempt to explain all the devices which serve to adapt the foot to its use. Is there anything in the life of the bird that would make the correlation of the adaptation of the foot for scratching and perching? Note the method of walking in a sparrow, robin, and pigeon. What is there about the position or structure of the leg that adapts it for walking or hopping? In the ostrich and cassowary the wings are not used for flight;

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Explain, after reading the paragraph on adaptation in the lower limbs, how each of the above feet are fitted to do their work. From photograph loaned by the American Museum of Natural History.

Notice

here the lower limbs have taken up the function of rapid motion. any adaptations for aquatic life that you may find, and explain in each case how the part described is fitted for the work to be done. The foot of the common barnyard duck, for example, is much like that of the alligator.

The Skeleton. The whole skeleton combines lightness, flexibility, and strength. Many of the bones are hollow or have large spongy cavities. The bones of the head and neck show many and varied adaptations to the life that the bird leads. The vertebræ which form the framework of the neck are strong and

yet flexible. They vary greatly in shape and also in number. The swan, seeking its food under water, has a neck containing twenty

three long vertebræ; the English

sparrow, in a different environment, has only fourteen short ones. Some bones, notably the breastbone, are greatly developed in flying birds for the attachment of the muscles used in flight.

Bill. The form of the bill shows adaptation to a wonderful degree.

Exercise for a Trip to a Museum or Zoological Park. Note a number of different-shaped bills. How is the bill adapted to taking the food for the bird? Seek for uses in each case. Remember that a bird uses its bill as some animals use claws and teeth. Birds, except the parrot and some of the birds of prey, rarely use the claws in feeding. The bills vary greatly according to the habits of the birds. A duck has a flat bill for pushing through the mud and straining out the food; a bird of prey has a curved or hooked beak for tearing; the woodpecker has a sharp straight bill for piercing the bark of trees in search of the insect larvæ which are hidden underneath.

Skeleton of a fowl; C., clavicle; C. V., cervical vertebræ; K., keeled sternum; P.G., pelvic girdle; Pc.G., pectoral girdle.

Birds never have teeth, except possibly in the embryo stage. The edge of the bill may be toothlike, as in some fish-eating ducks; these, however, are not true teeth. Frequently, too, the tongue has sharp toothlike edges which serve the same purpose as the recurved teeth of the frog or snake. With care you may be able to make out the use of the tongue in eating and drinking in some bird. Report in class the result of your observations.

Reason for High Temperature and Rapid Heart Beat in Birds. Make observations on a bird as to the rapidity of the movements made in breathing (respiratory movements). Compare them with your own as to rapidity. Compare the rate of heart beat in your own body and that of a bird (a live sparrow or canary). To take your own pulse, find the artery in your wrist or on the side of your head about an inch above the midpoint, on a line between the ear and eye. The heart of the bird may easily be felt by holding the hand against its breast. If now the temperature of the body of the bird be taken (by holding a clinical thermometer under the wing), and this compared with that of your own body taken under the arm, a considerable difference will be noticed.

The rate of respiration, of heart beat, and the body temperature are all higher in the bird than in man. All these correlated facts show that, because of the increased activity of the bird, there comes a necessity for a greater and more rapid supply of oxygen, an increased blood supply to carry the material to be used up in the release of energy, and a means of rapid excretion of the wastes resulting from the process of oxidation. The bird may be compared to a high-pressure steam engine. In order to release the energy which the bird uses in flight, a large quantity of fuel which will oxidize quickly must be used. Birds are large eaters, and the digestive tract is fitted to digest the food quickly and to release the energy when needed, by having a large crop in which food may be stored in a much softened condition. As soon as the food is part of the blood it may be sent rapidly to the places where it is needed, by means of the large four-chambered heart and large blood vessels.

This is one of the greatest adaptations to the active life led by a bird. Man breathes from twelve to fourteen times per minute. Birds breathe from twenty to sixty times a minute. The lungs are not large, but the bronchial tubes are continued