38 HOMING AND RELATED ACTIVITIES OF BIRDS. 



NESTING ACTIVITIES OF NODDIES. 



The noddy tern builds its nest usually in the bay-cedar bushes, of whatever 

 material it can find; small twigs (plate 4, fig. 1), seaweed, and shells are all 

 used. At times the nest is placed on low-growing grasses (plate 3, fig. 2) and 

 cacti, rarely on the bare ground. Both birds work upon the nest. Usually 

 several days are required to complete the structure. One egg is laid. The 

 period of incubation is 28 days. If the egg is removed, usually another egg is 

 laid. In this way it becomes possible to prolong to some extent the breeding 

 period. 



While the nest is under construction and during the period between the com- 

 pletion of the nest and the depositing of the egg, the male feeds the female 

 (plate 4, fig. 2). During all this time the birds are wild and beyond easy 

 means of control. As soon as the egg is laid the instinctive cycle changes and 

 the birds no longer fly out at the approach of the exiaerimenter. At this time 

 the noddy becomes a suitable subject for experiment on homing. At the 

 beginning of the brooding season proper, still another marked change comes 

 in the feeding instincts. Both birds brood the egg, shifting more or less 

 regularly at 2 to 5 hour intervals. At night both birds are invariably present. 



NESTING ACTIVITIES OF SOOTIES. 



The sooty tern usually scratches out a shallow depression in the sand (plate 

 4, fig. 3). Since 1907 the island has become covered with a dense under- 

 growth and bare stretches of sand are not common. The vast majority of the 

 eggs are now laid bare upon the earth or upon a leaf carpet. It is advisable, 

 where homing experiments are to be carried out, to clear out this undergrowth 

 in desirable areas. Observation of the nest is thus made easy. Clearing 

 away the undergrowth has one disadvantage by reason of the fact that in the 

 last few years the laughing gulls have become quite numerous on Bird Key. 

 They persistently rob both the noddy and the sooty nests. Some means 

 must be found for preventing their depredations. They were quite trouble- 

 some in 1913. 



The sooties, like the noddies, are wild until the egg is laid (in certain nests 

 two eggs are laid). During the brooding period they become quite bold and 

 are easily caught. The brooding period is about 31 days. Male and female 

 take regular turns at the nest. Shifts occur only once in 24 hours, however, 

 and at times only once in every 48 hours. For this reason it is always more 

 diflScult in homing experunents to determine the tune of arrival of the sooty 

 at night than that of the noddy. What becomes of the sooty when not on 

 the nest is difficult to say. The two occupants of a nest are rarely seen 

 together. We are inclined to think, though, that both birds are near the nest 

 at night. Close observation of the sooty is difficult unless the bird is marked. 

 There are probably more than 18,000 (possibly 30,000) sooties on Bird Key, 

 and the nests are often separated by a distance not greater than the length of 

 the bird (plate 4, fig. 3). Notwithstanding this crowded condition each nest 

 is accurately localized by its proprietors. Encroachments upon a nest or its 

 environs by a neighboring bird are fiercely punished by the owners. The nests 

 are carefully maintained all during the brooding period. When the young 

 bird is 10 to 12 days of age there is a gradual desertion. The young bird runs 

 to meet the parent and begins to feed at whatever place the meeting is effected. 



