To answer this question let us observe that at feeding visits 

 Nos. 17, 29, 39, 45, 50, 73, 86, 111, 133, and 198 a Mayfly did 

 evoke the swallowing reflex in White. And that on visits Nos. 

 100, 155, 228, 240, and 251, it was produced in White with a 

 green worm. Probably, then, the fault was not with the stim- 

 ulus. 



At visit No. 73, just four minutes before visit No. 75, White 

 had been fed a Mayfly, and had received another feeding nine 

 minutes previous to this. It seems fair enough to conclude that 

 the difficulty was internal; either the reflex mechanism was 

 fatigued, or the presence of food in the stomach set up a reflex 

 which inhibited the swallowing reflex. At visit No. 133 a Mayfly 

 was offered to the Cowbird, but the swallowing reflex not being 

 promptly shown, the food was given to White, as recorded. 



Sometimes this insistence by the adult on a quick response of 

 the reflexes may work to the detriment of the young, as illus^ 

 trated in the following incident. At visit No. 107 the female 

 bird brought a large green worm, a quarter of an inch in diam- 

 eter and an inch and a half long — of sufficient thickness to 

 greatly distend the gullet of the nestling. White was tried and 

 responded but the worm entered the gullet slowly, and the mother 

 became impatient and jerked the worm to give it a new start, 

 or to test another young one. White, however, held on, or could 

 not let go, and was pulled out onto the rim of the nest, from 

 which he toppled over and fell to the ground. As this was hap- 

 pening the mother bird hopped over and ca.ught hold of the 

 green worm in White's mxDuth, thus saving the worm which was 

 now promptly fed to the Cowbird. While the Cowbird had 

 nothing to do directly with the accident to White, yet it 

 would not have happened, probably, if the big Cowbird (at least 

 twice the size of either Vireo) had not been present to fill up the 

 cavity of the nest. After feeding the Cowbird the mother bird 

 looked carefully into the nest,, as if to see what had happened, 

 but immediately flew away, apparently without further concern. 

 White was then replaced in the nest by the observer. 



Regurgitation 



Although the young were a few days old at the time of ob- 

 servation, a very careful watch was kept for evidence of re- 



28 



