212 Papers from the Marine Biological Laboratory at Tortugas. 



ACTIVITIES BY THE NODDY AFTER THE EGG IS HATCHED. 

 The period of incubation varies for the noddy from 32 to 35 days. This 

 fact was determined on the basis of 16 observations. The young began to 

 appear on the island about May 9 (1907). The development of the young 

 of both species is discussed separately further on in this paper. Under the 

 [iresent heading I shall mention only the change that the presence of the 

 young brings in the behavior of the parents. At this period there is an 

 increased tendency to defend the nest. They will now attack with vigor 

 other noddies which approach too near the nest, the sooties and the frigate 

 birds {Fregata aquila). From the writings of others I had drawn the con- 

 clusion (i) that the frigate-bird attacks the terns and forces them to 

 disgorge, and (2) that it feeds upon their }oung. I spent many weary hours 

 in attempting to discover the relation of the frigate-bird to the terns, 

 especially its relation to the noddies. Since the noddies build their nests 

 in the bushes where the frigate-birds roost, it was presumed that there if 

 anywhere the devouring tendency of the frigate-bird ought to appear.' I 

 found that the cause of the disturbance between noddy and frigate-bird lies 

 chiefly in the fact that the latter, in attempting to find a bush in which to 

 rest, sun, or roost, will oftentimes alight upon or very near to a noddy nest, 

 whereupon the nodd\' most immediately concerned and those nearby will 

 attack the frigate-bird and at times even rout him. It is a common occur- 



' When I first went to the island, about 50 frigate-birds were present. The 

 number gradually increased during my stay, until at the end 400 to 500 were present. 

 I caught and forced a number of these birds to disgorge (which they readily do), 

 for the purpose of finding whether or not the remains of young terns or of very 

 small minnows, the food of the terns, could be discovered in the stomach contents. 

 I found that the staple article of diet with them is the flying-fisli, which they can 

 easily catch. At times I found fairly large herring and mullet. I also killed 2 of 

 these birds, but found no traces of young terns. In one case the stomach cavity 

 contained no food. This latter observation was interesting in view of the fact that 

 for days during unpleasant weather these birds apparently do not leave the island. 

 This fact made me think at first that possibly the young terns were preyed upon 

 by the frigate-birds in bad weather, but I am convinced that the latter can go with- 

 out food for long periods of time. On the other hand, it must be confessed that 

 after the young terns appear the number of frigate-birds increases and that all 

 during the day, when the sooties nesting in the open places are feeding their yoiuig, 

 the frigate-birds line the bushes bordering upon the nests. At times a frigate-bird 

 will swoop down and flv near the ground. This causes all the sooties to fly tip 

 and raise a terrible commotion. This soon subsides, only to be repeated an instant 

 later when another frigate-bird flies to or near the ground. I built an observatory 

 on top of the house and a tent in the midst of the nesting-places, and kept the 

 whole island under close inspection with a field-glass (in this connection I wish to 

 thank the firm of Bausch and Lomb for the use during my entire stay of an excel- 

 lent stereo-binocular field-glass) in order to determine whether the fngate-bird when 

 it made these movements actuallv picked up the young or whether it was attempting 

 to pick up food which the parent bird had dropped while feeding the young. My 

 efforts were unsuccessful, so far as showing that the frigate-bird really does vio- 

 lence to the young tern or filches its food. The sooty, in contrast to the noddy, never 

 attacks the frigate-bird. 



All that I have read about the ability of these birds to control their movements 

 during flight is true. I have observed them many times in mid-air forcing a victim 

 of their own species to disgorge a fish, which one of the pursuers would catch long 

 before it struck the water. 



