302 Papers from the Marine Biological Laboratory at Tortugas. 



nests attempting to establish sexual relations with these temporarily un- 

 guarded females. This is in all cases unsuccessful. Disturbance to some 

 extent is also caused by other birds attempting to poach straws. If the day 

 is hot, the female may make frequent trips to the water. The nest is thus 

 left for a time unwatched. The bird quickly returns, however, and resumes 

 watch over it. 



The male returns with a full-laden crop. He alights directly upon the 

 nest or near the female. The female at once shows signs of life, and as 

 thev approach each other they begin nodding. Then the male invites the 

 female to feed by putting his beak down to a position convenient to her. She 

 gets the food by taking it directly from the mouth of the male, the male 

 disgorging it bv successive muscular contractions of the throat and abdo- 

 men. The impression one gets from this ludicrous performance is that the 

 bird is choking to death. During the whole of the process of feeding, a 

 soft, nasal, rattling purr is emitted, presumably by the female. This purr- 

 mg sound is an invariable indication that feeding is taking place. It is to be 

 heard on no other occasion. 



At times the male upon his return is not so ready to feed the female. 

 The female then strikes the bill of the male sharply with her own. I have 

 seen the female thus strike the male i8 to 24 times before eliciting the 

 proper response from him. On other occasions, the female is reluctant to 

 feed the proper length of time, whereupon the male gently taps the female 

 and puts his beak near her own again and again. The controlling stimuli 

 throughout this reaction seem to be organic and z'istial. We might schema- 

 tize the principal features of the reactions, as a whole, as follows : 



The male fishes until intra-organic pressure of food in the crop reaches 

 a certain intensity. This acts as a stimulus to return (proximate and dis- 

 tant orientation discussed on pages 224 and 227 respectively). The visual 

 stimulus of mate (and nest and nest locality) coupled with the intra-organic 

 stimuli just mentioned, condition the feeding reaction. On the part of the 

 female we have the intra-organic (hunger) stimulus and the visual stimulus 

 induced by the movements of the male. The male disgorges until there is a 

 cessation of the excessive intra-organic pressure, at which time his feeding 

 movements cease and the female may strike his beak in vain. The female in 

 her turn feeds until there is both a cessation of hunger and a normal intra- 

 organic pressure established. If this takes place before the male is ready, he 

 in turn attempts to further stimulate the female by a slight change in behavior 

 (i. e., "coaxing" by tapping the female and putting his beak down near her). 

 The feeding reaction completed, the birds often sit near each other, nest- 

 ling and nodding vigorously. This is the time usually chosen for coition, 

 which takes place frequently up to the time the egg is laid. Feeding may 

 occur at any time of the day, but the best time to observe it is at sunset, 

 when the males are returning in numbers. 



