BIRD HABITS 305 



many cases. The memory and leadership of old birds, though 

 often helpful, cannot account for migration of young by them- 

 selves to lands they have never seen. We have to assume an 

 instinct of migration and a " sense of direction " developed to a 

 degree that we can only imagine, and that is really no explanation 

 at all. 



Economic Importance of Birds. There is no group of animals to 

 which man is more indebted than the birds. It is highly probable 

 that without their aid, agriculture would be impossible, because of the 

 vast quantity of insect pests and weed seeds which they destroy. 

 The accompanying table shows the nature of the food which they 

 eat, and it is well to remember that they eat early and often. 



Their greatest service is in the destruction of harmful insects 

 both as egg, larva, and adult. In some states where general bird 

 killing was permitted the insect enemies of crops increased to such 

 an alarming extent that stringent laws were put in force. 



An unwise bird law cost the state of Pennsylvania nearly four 

 million dollars in a year and a half through the destruction which 

 it permitted among useful birds. At the end of this period, the 

 damage was so apparent that they repealed the law and appointed 

 a state ornithologist to look after the birds. Actual experiments 

 have been worked out with protected and unprotected bird regions 

 so that the fact of their essential service can no longer be 

 questioned. 



Next to their destruction of harmful insects comes their work 

 against the seeds of weeds which, as the table shows, constitute 

 a large part of their diet. Many of the larger birds, such as hawks, 

 owls, and jays, destroy mice, rats, and other harmful vermin. 

 Some, like the crow, vulture, and buzzard, act as scavengers. 



Almost as important are the products which man obtains from 

 the birds. Our domestic fowls produce flesh and eggs to the amount 

 of over half a billion dollars annually. This does not include the 

 value of game or wild birds. Feathers for millinery and bedding 

 are another valuable bird product, and where the feathers are 

 those of food birds, it is a perfectly legitimate one. In some 

 Pacific islands, where millions of sea birds have roosted for centuries, 



