30 BIRDS OF CALIFORNIA AFFECTING FRUIT INDUSTRY. 



FOOD OF YOUNG. 



Among the stomachs examined were those of 22 nestlings, varying 

 in age from 2 days to those just ready to leave the nest. They were 

 taken from Ma}' 30 to July 2, inclusive. In order to ascertain if im- 

 portant differences exist between the food of the adults and that of the 

 young, the contents of these stomachs were tabulated separately. 

 Comparison shows little or no difference in the quantity of vegetable 

 matter eaten bv adults and young;. 



The animal matter in the food of the young is precisely of the 

 same kind as eaten by adults, but the proportions are rather differ- 

 ent. Hymenoptera are the largest item in the food of the young 

 as well as of the parent birds, and amount to ¥2 percent for 

 the former against 39 percent for the latter. Diptera stand next in 

 importance, with 80 percent for the young against 12 percent for the 

 adults. As these insects are mostly soft-bodied, it is the usual custom 

 of birds to feed a greater proj^ortion of them to the young. Hemip- 

 tera amount to a little more than 16 percent of the nestlings' food, 

 while the adults eat them to the extent of nearly 27 percent. Beetles 

 are fed to the young to the amount of about 10 percent, while the 

 parents eat them to the extent of 10 percent. This again might 

 naturally be expected, as most beetles are hard and less easily 

 digested than flies and some other insects, and hence are less suitable 

 food for 3^oung birds. 



From the foregoing it is evident that the food of young cliff 

 swallows does not differ in kind from that of the adults, but is dis- 

 tributed among the various orders of insects in somewhat different 

 proportions. Hymenoptera and Diptera constitute nearly three- 

 fourths of the diet, evidently because they are soft and easily broken 

 up and digested. Beetles and bugs appear in the stomachs less 

 frequently. While beetles are not extensively eaten, it is worthy of 

 note that the variety is considerable, as representatives of no fewer 

 than 10 species were contained in the stomach of one nestling. One 

 stomach held a few bits of eggshell, and gravel was identified in 

 two others. One of these contained 7 good sized gravel stones; the 

 other, pieces of glass and gravel. The supposed function of gravel 

 in the stomachs of birds is to assist in breaking up. the food. That 

 gravel should be given young cliff swallows wdien not taken by the 

 adults is remarkable. The feeding of gravel to the young has been 

 noted in the case of other species of swallows. 



WESTERN BARN SWALLOW. 

 (Hirundo erythrogastra.) 



The barn swallow is rapidly learning, not only that the structures 

 built by man afford excellent nesting sites, but that the presence of 



