Section 2

Characteristics of Birds

• Contour feathers are made of a central shaft composed of two vanes with branches, called barbs, that are connected by interlocking hooked barbules.

• Two modifications to the bird skeletal system include an enlarged sternum and hollow bones.

• The crop stores food. The two parts of the stomach are the proventriculus and the gizzard, which crushes food.

• The lungs of a bird are connected to several air sacs that store and move air but do not participate in gas

• Birds lack a urinary bladder and excrete their nitrogenous waste as uric acid mixed with feces.

• The cerebellum, cerebrum, and optic lobes of the bird brain are large.

• All birds lay hard-shelled eggs. Precocial young are active as soon as they hatch. Altricial young are born helpless and require parental care for several weeks.

• Many birds migrate using a variety of environmental cues to guide their migration.

Vocabulary feather (p. 844) follicle (p. 844) shaft (p. 844) vane (p. 844) barb (p. 844)

barbule (p. 844) preen gland (p. 844) sternum (p. 845) pygostyle (p. 845) crop (p. 846)

proventriculus (p. 846) gizzard (p. 846) vas deferens (p. 848) oviduct (p. 848) brood patch (p. 848)

precocial (p. 849) altricial (p. 849) ornithologist (p. 849)

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