578 MAN AS A CONQUEROR 



Agriculture (Division of Biological Survey) show that a surprisingly 

 large number of birds once believed to harm crops really perform 

 a service to farmers by killing injurious insects. Even the much 

 maligned crow eats, as well as grain and fruit, mice and harmful 

 insects, notably grasshoppers, and feeds its nestlings many more. 

 A. H. Howell, in Bulletin 29 of the Biological Survey, hsts 85 species 

 of birds known to eat boll-weevils, based on stomach examinations 

 of 3114 birds. The bluebird includes grasshoppers, ants, spiders, 

 weevils, tent caterpillars, army-worms, cutworms, and the codling 

 moth in its diet. Swifts and swallows eat flies, and cuckoos and blue 

 jays eat hairy caterpillars, relished by few other birds, while much of 

 the winter food of chickadees consists of eggs of aphids or plant lice. 

 Ants are eaten by many species of birds. Larvae of beetles, mostly 

 injurious, are preferred by crows, blackbirds, and robins. Many 

 observations indicate that nesting birds eat a large amount of food in 

 proportion to their size, and consequently destroy vast numbers of 

 injurious insects. A young robin three weeks old has been observed 

 to eat 70 cutworms in one day ; a young tanager, 150 cutworms in a 

 day besides other food ; and a young phoebe just out of the nest, as 

 many as 200 good-sized grasshoppers in a day. 



In addition to eating insects, nearly 300 species of birds eat the seeds 

 of weeds and other injurious plants. Our native sparrows, the mourn- 

 ing dove, bobwhite, rose-breasted grosbeak, horned lark, crow black- 

 bird, and other birds feed largely upon the seeds of numerous common 

 weeds. An examination of the stomachs of a number of these birds 

 showed that they had consumed over one hundred kinds of weed seeds. 

 Tree sparrows alone are estimated to eat 875 tons of weed seeds every 

 winter in the state of Iowa. 



Some birds, such as cormorants, pelicans, herons, ospreys, bitterns, 

 kingfishers, gulls, and terns, are active fishers, and thus may destroy 

 food fish and distribute parasites. But gulls, as well as the buzzards 

 of the West and South and the vultures of India and semitropical 

 countries, are of immense value as scavengers. Birds of prey (hawks 

 and owls) eat living mammals, including many harmful rodents, such 

 as gophers, field mice, and rats. 



In addition to their commercial value, mammals are useful in 

 many ways. Browsing cattle keep down weeds, along with their 

 consumption of grass and other forage. A few mammals are insectiv- 

 orous, notably bats and moles, both of which destroy injurious insects. 

 Some carnivorous animals, such as skunks, weasels, raccoons, coyotes. 



