598 TEXTBOOK OF ZOOLOGY 



guano accumulates at the rate of about four inches a year or 750 

 tons per acre per year. Large numbers of different kinds of birds 

 render service of almost inestimable value in destroying insects, 

 rodent pests, and weed seed. The hawks and owls are very im- 

 portant as rat and mice killers. Finches, sparrows, and quails are 

 destroyers of weed seed. Woodpeckers, chickadees, creepers, wrens, 

 bluebirds, robins, thrushes, flycatchers, kingbirds, meadow larks, 

 swallows, warblers, tanagers, vireos, and many others are very im- 

 portant insect feeders. This asset, if computed financially, would 

 run into millions of dollars a year for the country. At the same 

 time the value of the birds as game for sportsmen to hunt cannot 

 be measured wholly in dollars and cents. 



DOMESTIC CHICKEN 



Gallus domestica Cbankiva), the domestic fowl, is a convenient ani- 

 mal for study because of its size, its availability, and its universal 

 distribution with man. As previously stated, it is thought to have 

 arisen from the Indian jungle fowl. It is of great interest, not only 

 because of its immense economic value, but because it shows many 

 of the adaptations of this form of animal to its ij^e of life. Although 

 the chicken has partially lost its power to fly, it still retains the 

 features which adapt birds to a life in the air, such as feathers, 

 wings, air sacs, hollow bones, and a rigid skeleton. The principal 

 modification of the chicken from its wild ancestors is the relative 

 increase in weight to give the body a stocky build, failure to de- 

 velop and exercise the short wings, and a great increase in egg 

 production in most breeds. 



Habits and Behavior 



This is a diurnal perching bird which spends the time between 

 dusk and daylight sleeping in a squatting position on a perch. 

 During the daylight hours it is an extremely busy animal at hunt- 

 ing food, dusting feathers, running, walking, scratching, and for the 

 females, egg-laying. The flocking habit is fairly well developed, 

 and usually one cock establishes himself as master of a certain flock 

 and all other cocks are more or less subservient to him. They are 

 entirely polygamous and the mating is promiscuous. 



