378 



PRACTICAL ZOOLOGY 



carried on by the United States Department of Agriculture, 

 state governments, and private parties in order to learn the 

 relations of birds to man with regard to the destruction of in- 

 jurious animals. The results of these researches may be found 

 in government publications or in books such as Weed and Dear- 

 born's Birds in their Relation to Man, and Forbush's Useful 

 Birds and their Protection. 



NESTLING 



FIG. 258. Food of nestling house 

 wren. 



ADULT. 



FIG. 259. Food of adult house wren. 

 (U. S. Dept. of Agric.) 



A very large proportion of the food of birds consists of insects. 

 Figures 258 and 259 show diagrammatically the food of nestling 

 and adult house wrens, birds that are very common about gar- 

 dens. Practically all of the insects devoured by birds are 

 injurious to plants or animals and consequently harmful to 

 man. 



Another large element in the food of birds consists of small 

 mammals, such as field mice, ground squirrels, and rabbits. 

 For many years hawks, owls, and other birds of prey have been 

 killed whenever possible, because they were supposed to be in- 

 jurious on account of the poultry and game birds they captured. 

 Careful investigations have shown, however, that at least six 

 species are entirely beneficial ; that the majority (over thirty 



