Development and Care of the Young 193 



avoid any defilement of the nesting site. The use of the excreta 

 as food, however, is not to be regarded as due to inheritance. 



Much light is thrown on this question by the behavior of the 

 Chestnut-sided Warblers, whose habits will be referred to again 

 in the concluding chapter. Both sexes in this case fed, brooded, 

 and cleaned the young and nest. The male regularly removed 

 the excreta but was never seen to eat it. The female on the 

 contrary often ate of it, and brooded so constantly that she was 

 obliged to leave the nest to satisfy her own hunger. She would 

 often be back in half a minute, having taken only a bite as it 

 were. When the female had received the food which her mate 

 supplied and had seen it safely delivered, she would inspect, 

 devour everything which needed removal, and then continue to 

 brood. If a sac should accidentally fall, she would snap it off 

 the ground, return to the nest, and brood as before. At other 

 times when the male approached she would stand aside and 

 allow him to deliver the food and make the inspection. Twice 

 I saw the male take a sac to carry it away, and the female snatch 

 it from him, swallow it, and settle down on the nest. Again 

 another sac was torn asunder, and each bird went off with a 

 half in its bill. In a moment the female returned but without 

 bringing food, showing that she had been satisfying her own 

 hunger. This not only proves that the excreta is used as food 

 but illustrates how the habit of eating it may be forced upon a 

 hungry brooding bird. 



Since digestion in the young is an imperfect process at best, 

 it is easy to understand how any kind of pre-digested or partly 

 digested food might be acceptable in times of stress when the 

 staple article was not easy to procure. The fact that a bird 

 only casually devours a pellet or swallows one and removes an- 

 other is easy to understand. It is a question of the hunger of 

 the moment, and another illustration of the economy which 

 birds display in all such matters. 



While the removal of the excreta is an instinctive act, the 

 use of it as food is probably an acquired habit, the strength 

 of which depends on the force of circumstances, and may be 



limited in some cases to one sex alone. 

 13 



