are evidently for protection against cold and wet, but later in life they serve other uses. The feathers of most male birds are brightly colored. This seems to make them attractive to the females of the species; thus the male may win its mate.

Adaptations in the Lower Limbs.-The ankle of a bird is extremely long and reptile-like. Scales are found on the ankle and foot. The most extraordinary adaptations are found in the feet of various birds. Some have the foot adapted to perching, others for swim

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

ming, others wading, etc. We are able, by looking at the feet of a bird, to decide almost certainly its habitat, method of life, and perhaps its food.

In the perching birds we find three toes in front and one behind, the hind toe playing an important part in holding the foot in place. In swallows, rapid and untiring flyers, the feet are small. In the case of the parrots, where the foot is used for holding food, climbing, and clinging, we find the four-clawed toes arranged two in front and

two behind. Hawks and eagles are provided with strong talons with which the prey is seized and killed.

Adaptation for semiaquatic life is seen in plovers, herons, or storks, where long legs and long toes enable the birds to seek their food in soft mud among reeds or lily pads, or along sand flats. True aquatic birds, on the other hand, are provided with webbed toes. The foot of the common barnyard duck, for example, is much like that of the alligator. In the ostrich and cassowary the wings are not used for flight; here the lower limbs have taken up the function of rapid motion.

Perching. The habit of perching is an interesting one. In many perching birds the tendons of the leg and foot, which regulate

Skeleton of a fowl: C, clavicle; CV, cervical vertebræ; K, keeled sternum; PG, pelvic girdle; PcG, bones of pectoral girdle (except clavicle).

the toes, are self-locking; while asleep such birds hold themselves perfectly. A certain part of the ear, known as the semicircular canals, has to do with the function of balancing. In the flamingoes and other birds, which do not perch, balancing appears to be automatic; thus the bird is able 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. Most birds have under the skin of the tail a large oil gland, whence comes the supply of oil that is used in waterproofing the feathers in preening.

The Skeleton. The skeleton combines lightness, flexibility, and strength. Many 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 flexible. They vary in shape and

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, the bills varying greatly according to the habits of the birds.

Adaptations in the bills of birds. Could we tell anything about the food of a bird from its bill? Do these birds all get their food in the same manner? Do they all eat the same kind of food?

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.

Birds do not have teeth. The edge of the bill may be toothlike, as in some fish-eating ducks; these, however, are not true teeth. Frequently the tongue has sharp toothlike edges which serve the same purpose as the recurved teeth of the frog or snake.

Adaptations for Active Life. The rate of respiration, of heartbeat, and the body temperature are all higher in the bird than in

man.

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, the bronchial tubes being continued through the lungs into hollow spaces filled with air, which are found between the organs of the body. Only the lungs, however, are used for breathing. Because of the increased activity of a 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. A bird may be compared to a high-pressure steam engine; in order to release the energy which it 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 fourchambered heart and large blood vessels.

The high temperature of the bird is a direct result of this rapid oxidation; furthermore, the feathers and the oily skin form an insulation which does not readily permit of the escape of heat. This insulating cover is of much use to the bird in its flights at high altitudes, where the temperature is often very low.

The Nervous System and the Senses. - The central nervous system is well developed. A large forebrain is found, which, according to a series of elaborate experiments with pigeons, is found to have to do with the conscious life of the bird. The cerebellum takes care of the acts which are purely mechanical.

Sight is probably the best developed of the senses of a bird. The keenness of vision of a hawk is proverbial. It has been noticed that in a bird which hunts its prey at night, the eyes look toward the front of the face. In a bird which is hunted, as in the dove, the eyes are placed at the side of the head. In the case of the woodcock, which feeds at night in the marshes, and which is in constant danger from attack by owls, the eyes have come to lie far back on the top of the head. Hearing is also well developed in most birds; this fact may be demonstrated with any

canary.

The sense of smell does not appear to be well developed in any bird, and is especially deficient in seed-eating birds.

Nesting Habits. Among the most interesting of all instincts shown by birds are the habits of nest building. We have found that some invertebrates, as spiders and ants, protect the eggs when laid. In the vertebrate

a nest, in which to rest, is needed. The ostrich is an exception; it makes no nest, but the male and the female take turns in sitting on the eggs. Such birds as are immune from the attack of enemies because of their isolation or their protective

ing nest of the oriole. Some nests which might be easily seen because of their location are often rendered inconspicuous by the builders; for example, the lichen-covered nest of the humming birds.