BIRD ROOKERIES OF TORTUGAS BARTSCH. 485 



year to year, some of the oldest nests have grown to enormous size, due to 

 the addition of new materials at each successive season. 



Both birds work, bringing sticks, seaweed, shells, and coral. Both birds 

 shape the nest clumsily by pecking and pulling at the sticks. They never 

 weave the sticks so as to form a compact and durable nest. The stick is 

 dropped on the rim, then drawn into position. Frequently, first one bird, then 

 the other, sits in the nest and shapes it. In order to do this the bird rises on 

 its feet and depresses its breast and turns round and round. The material 

 is obtained both far and near. Floating sticks and seaweed are gathered 

 from the water. They frequently alight under the nests of other birds and 

 gather up the fallen branches. They even take the material from other nests 

 which are left momentarily unguarded. Frequently fights ensue. The birds 

 work neither steadily nor rapidly ; 10, 15, 20 minutes elapse before either 

 makes a trip. 



Very often the nest has the appearance of being constructed directly upon 

 the ground, but a closer examination usually shows that it has been built 

 upon a tuft of grass or upon the stem of a bush, the branches of which have 

 been broken off close to the ground. The nearest approach I found to the laying 

 of the egg upon the bare ground was in the case of two nests built on a bare 

 horizontal board lying among the cactus growth. In each of these cases the 

 egg was laid directly upon the board, but some dozen or two small sticks re- 

 tained the egg in position. * * * 



While observing the noddies at work upon the nest, it soon became apparent 

 that the daily routine of the female was different from that of the male. From 

 many hundreds of observations it was also evident that the male feeds the 

 female at more or less regular intervals. * * * 



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 they ap- 

 pi-oach each other they begin nodding. Then the male invites the female to feed 

 by putting his beak down in a position convenient to her. She gets the food 

 by taking it directly from the mouth of the male, the male disgorging it by 

 successive muscular contractions of the throat and abdomen. The impression 

 one gets from this ludicrous performence 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 purring sound is an invariable indi- 

 cation that feeding is taking place. It is to be heard on no other occasion. 



After the egg is laid a marked change appears in the behavior of both the 

 male and the female. The birds will attack even a human intruder, and 

 their defense of the nest against their own kind becomes even more strict than 

 before. Oftentimes the birds will sit on the egg and allow themselves to be 

 caught, striking viciously all the while with their long, keen, pointed beaks. 

 Individuals vary greatly in this respect. On my daily rounds, as I approached 

 the vicinity of a group of nests, several noddies would usually advance to meet 

 me, striking viciously at my head. Their attacks would continue until I 

 withdrew. Many times I have had my hat knocked off and the blood brought 

 from my scalp by their vicious attacks. 



Still another marked change occurs in the habits of the birds : The male no 

 longer feeds the female. Each bird takes equal turns at brooding the egg. 

 My attention was first called to this while I was watching the habits of the 

 birds before the egg was laid. Several nests in the vicinity of the place of 

 observation already contained eggs. At these nests I was never able to ob- 

 serve the feeding of the female by the male. At this period the two birds become 

 practically automata. Their life is taken up in alternately brooding the egg 



65133°— sm 1917 32 



