2 14 Papers froin the Marine Biological Laboratory at Tortugas. 



The young are cared for in the nest until they become strong enough to 

 leave it and live upon the ground. The young birds born in low nests, even 

 at a very early age (20 days and even earlier), clamber from them with 

 alacrity and hide in nearby bushes when danger is imminent. In many cases 

 these young birds can not get back into the nest. Under these circum- 

 stances they remain near the nest locality, and the parents on returning first 

 alight on or near the nest and later hop to the ground and feed the young 

 bird. It is interesting to speculate upon the method of recognition between 

 parent and young. There can be no doubt at least of an accurate functional 

 recognition. Since the noddy is always silent when contented, the evidence 

 is good that recognition occurs wholly in terms of vision. Whether recogni- 

 tion of young (or of mate by mate) would take place outside of the nest 

 locality is a problem which ought to be solved. 



On account of my early departure from the island (July 18) I can say 

 nothing of the methods by which the parents induce the young to fly, to 

 leave the island and to feed. This period is probably one of great inter- 

 est. At the time of my departure many of the young noddies were on the 

 ground and were attempting to fly. If I may be allowed to advance state- 

 ments which lie beyond my actual observation, I should say that the parents 

 are not active at all in " training " the young to fly and to feed. 



As the young birds advance in age the parents more and more often 

 engage in the " sunning reaction." My opinion is that the young birds first 

 instinctively collect upon the beach, as soon as their wings will support them. 

 In a short time the instinct to follow the adults leaving from this point to 

 go to food will lead them out over the water. The sight of the jumping fish 

 is a stimulus leading to the movements used in catching the fish. This 

 activity engaged in a few times so perfects the hereditary mechanism that 

 the bird soon becomes independent of the parent in an environment where 

 food is abundant. 



In summarizing this section we may say : ( i ) that the parents alter- 

 nately feed the young at intervals varying from i to 4 hours; (2) that their 

 general conduct is not greatly changed at the time of the appearance of the 

 young, the changes actually observable being an increased tendency to pro- 

 tect the nest and to disgorge on being disturbed.^ 



My own observations naturally contain nothing concerning the behavior 

 of these birds when preparing for southern migration. Thompson^ writes 

 as follows (concerning both noddies and sooties) : 



Towards the end of September the birds begin to leave. They leave in great 

 flocks and at night. The entire exodus consumes, apparently, but two or three days; 

 and some morning the observer will find the island absolutely deserted, save for a 

 few crippled birds that have been injured and are unable to follow their comrades. 



' As the young advance in age (20 days and at all later ages) the parent will 

 readily leave the nest when disturbed. The tendency in this respect is to revert to 

 the behavior exhibited during the egg-laying season. 



= Op. cit., p. 82. 



