68 FOOD HABITS OF THE GROSBEAKS. 



Animal Food. 



Insects and other animal matter eaten by the black-headed gros- 

 beak amount to almost twice the bulk of the vegetable food, or 65.85 

 percent of the total subsistence. These, then, should be regarded as 

 the really staple foods of the species. While no single vegetable ele- 

 ment was fed upon by more than 41 grosbeaks, certain items of the 

 insect diet were chosen by more than a hundred, or over half of the 

 birds examined. This fact suggests that if the majority of the insects 

 preyed upon are noxious, the benefits conferred by the bird greatly 

 outweighs the injury inflicted. 



Coining, then, to the economic status of the insects devoured, it 

 appears from the results of the examination of 226 stomachs that 3.37 

 percent of the bird's food consists of ground beetles, fireflies, and 

 ladybirds, which usually are considered beneficial ; 2.56 percent is 

 composed of wasps, ants, bees, etc., some of which are very useful, 

 some innocuous or harmful; and 1.17 percent is made up of a great 

 number of unrelated items, largely of neutral import, which, owing 

 to the fact that they are rarely eaten, have little significance. Thus 

 58.75 percent, or nearly three-fifths of the entire food, is composed al- 

 most wholly of insects which are a constant menace to agriculture. 



Of the above classes the beneficial kinds deserve first consideration. 

 The most important among them numerically are fireflies (Lam- 

 pyrida?), which are almost uniformly carnivorous, both as larva? and 

 as adults. Since they do much to check the increase of many other 

 insects, the destruction of large numbers would be injurious. Fifty- 

 two of the grosbeaks examined had fed upon fireflies to the extent of 

 2.38 percent of the whole food. Both adults and larva? were captured, 

 from 5 to 19 of the former and from 12 to 30 of the latter being found 

 in some stomachs. 



Among other useful insects which are attacked by the blackhead 

 are the ground beetles (Carabida?). Xineteen grosbeaks ate them, 

 and they amount to 0.99 percent of the food. Since so few of these 

 beetles are captured and as certain of them at times feed upon plants, 

 the injury is too slight to be noticed. 



Three black-headed grosbeaks ate small ladybird beetles which prey 

 upon scale insects and plant lice, two of them securing specimens of 

 an Australian coccinellid (Rhizobius ventralis, fig. 33). which was 

 introduced into California for the express purpose of destroying scale 

 insects. If the grosbeak destroyed many of these beetles, the bird 

 would have to be given a black mark, but when it is considered that 

 the blackhead feeds upon scale insects a large part of the time (more 

 than a fifth of its food consisting of scales), it is surprising that so 

 few of the ladybirds are devoured. 



Considerable liking, however, was shown for another group, the 

 Hymenoptera, part of which at least are beneficial. The most useful 



