288 FIELD ZOOLOGY. 



The labor of feeding the young birds, for all the day- 

 flying sorts, begins before sunrise and continues until 

 after sunset ; the appetites of the nestling seem insatiable ; 

 the meals, as we would call them, often averaging one 

 every two minutes. 



Birds which do not change their diet bring up their 

 young on the same sort of food as they themselves eat. 

 For instance, pelicans and terns bring up their young 

 principally on fish. But gulls, some species of which nest 

 in Missouri, Kansas, and Iowa, have developed a fondness 

 for soft- bodied insects and worms, and may frequently 

 be seen following the plow, searching the freshly-turned 

 furrows for fat angleworms. Exclusively insectivorous 

 birds, as cuckoos and swallows, feed their young on insects. 

 Pigeons and doves feed their young on starchy seeds. 

 Seed-eaters and birds of mixed diet, both animal and 

 vegetable, have powerful, muscular, grinding gizzards; 

 and may, in addition, as in the case of our barnyard 

 fowls, mocking birds, and some other birds partly fruit- 

 eaters, swallow sand or small pebbles along with their 

 food. Birds lack teeth, and some of them use this means 

 of supplying the lack, thus breaking up the food in the 

 gizzard rather than in the mouth. Those birds that live 

 on insects, worms, or soft-bodied vertebrates, have thin- 

 walled, comparatively weak, non-muscular stomachs. 



A further fact is interesting: those birds which in 

 the adult stage live on both animal and vegetable food 

 feed their young on an insect diet. This fact must not 

 be lost sight of in estimating the value of a bird. What- 

 ever the character of the stomach of the parent bird, the 

 nestling has, in most cases, a membranous sack with but 

 little development, and cannot digest anything but the 

 softest and most readily digestible substances. Vege- 



