THE FEEDING OF NESTLING BIRDS 199 



gives the meaning as " To throw or pour back, as from a deep 

 or hollow space; cause to surge back, as some mammals re- 

 gurgitate food already swallowed." 



These definitions seem to be eminently satisfactory, and I 

 venture to presume that they will find approval in the judgment 

 of most ornithologists. The idea of regurgitation, then, implies 

 the previous act of swallowing of food, with concomitant reflex 

 muscular activity. It seems reasonable to suppose that any 

 reversal in the direction of passage would just as certainly re- 

 quire muscular action. And there is plenty of evidence to show 

 that in the lower orders where true regurgitation occurs, such 

 muscular action is clearly present. Let me remind you of the 

 description previously quoted from Gross of the strainings and 

 wrigglings of the head and neck of the Yellow-billed Tropic 

 Bird in feeding the young; and of the muscular contortions 

 of the bittern as described by Gabrielson. The photographs 

 accompanying Fisher's account of the Laysan Albatross (11) 

 indicate a raising and lowering of the head during the process. 



Let us then consider that regurgitation cannot be accomplished 

 without muscular effort, involving the pharyngeal muscles. 



It may be objected that the position of all passerine birds in 

 feeding is such as to permit gravitational regurgitation; that 

 when the stomach and crop are higher than the head, the food 

 may run down into the buccal cavity. Bearing in mind the 

 collapsible nature of the esophageal walls when at rest, gravi- 

 tational regurgitation does not seem to be a tenable hypothesis, 

 and is not entitled to serious consideration until substantiated 

 with some concrete evidence. 



For the Coccyges Herrick's account of the life history of the 

 Black-billed Cuckoo (10) is very complete. He makes no 

 explicit statement as to regurgitation but the inference is easily 

 drawn that he did not observe it. 



In the case of the Pici the evidence for regurgitation seems 

 to be good. Mr. William Brewster (12, pp. 233-235) gives 

 a very complete description of the process of feeding the nestling 

 of the Flicker. The parent approached the nest with the 

 mandibles shut, no food visible; when the parent's bill was 

 thrust into the nestling's throat there was a pumping movement 

 accompanied by corresponding twitching of the tail and hinder 

 parts of the body, and a slighter movement of the wings. As 



