LIFE HISTORIES OF NORTH AMERICAN GULLS AND TERNS. 281 



Within this charmed circle the two mated birds remain relatively quiet. 

 At this time sexual activity is at its height. It frequently happened in the sex- 

 ual process that the two birds would step ouside of their own territory and a 

 general fight would ensue. When the sexual reaction is in progress it is a sig- 

 nal for the surrounding males to encroach. Coition is thus completed only 

 after much fighting. I have seen the male attempt to mount the female 12 to 

 15 times, and at each attempt be interfered with by neighboring males. 



The actual construction of the nest, when a nest structure is formed, begins 

 after an undefended area has been found. The process of nest building is some- 

 what as follows : The bird puts the breast to the ground, thereby supporting the 

 body and leaving the legs comparatively free. The feet are used as a combined 

 scraper and shovel. A few backward strokes of the feet are made, which serve both 

 to loosen the sand and to remove it from beneath the body. The bird then turns 

 slightly and repeats the process. When it has turned 360°, or less, it begins to 

 use the breast as a shaper. By continuing this process the depression is soon 

 made to assume the required diameter and depth. My notes show that the 

 bay-cedar leaves are often gathered up and placed around the rim of the nest 

 as the hole is being dug. I can not say which sex does the work, but I believe 

 that both male and female engage in it. As soon as the depression is made both 

 birds begin to defend it. Naturally, where no nest is made, the nest site alone 

 is chosen and defended as described above. 



The nest of a sooty, when a nest is made, consists of a shallow oval depression 

 in the sand. This depression varies greatly in depth, depending upon the nature 

 of the surface. It is rarely over 5 centimeters in depth, even in loose sand. 



The northern and northeastern sections of the island are free from bushes, 

 but are covered by a shallow growth of Bermuda grass. These areas contain 

 by far the largest number of nests. The eggs in these areas are laid literally 

 on the grass and bare earth in ho kind of nest structure. The eggs are often 

 deposited in open sandy places, but nest depressions are not always made, even 

 where the nature of the surface easily permits It. 



A rather interesting variation in nest structure appears among certain nests 

 which are built under the bay-cedar bushes. The leaves from the bushes some- 

 times form a carpet over the sand. The nesting sooties often gather up these 

 leaves and place them around the rim of the depression. Under no circum- 

 stances are the leaves collected from a distance farther than the birds can 

 reach with their beaks while remaining in a sitting posture in the nest. 



Mr. B. S. Bowdish, (1900) found a large colony of these terns 

 breeding on Desecheo Island, near Porto Eico, under quite different 

 conditions, which he describes as follows : 



The nesting sites were ledges or shelves in the face of the rockv walls rang- 

 ing between 10 and 40 feet above the beach. Some were narrow and others 

 wide. In one case the egg was laid underneath a cactus plant on top of the 

 rocks, in some instances there seemed to be a slight gathering of rock chins 

 and small pebbles about the eggs in the form of a ring, and in a verv few 

 one or two bits of twigs were added, but otherwise there was no nesting ma- 

 terial, and often the egg laid on the bare rock. 



The Pacific form of the sooty tern (Sterna fuscata crissalis) breeds 

 on several islands on the west coast of Mexico and in the Hawaiian 

 group, congregating in vast colonies, surpassing in extent and density 



