2IO Papers from the Marine Biological Laboratory at Tortugas. 



remain awav over night? The nearest land (and the birds never swim 

 nor rest on the water) is 45 miles away (Marquesas, a very small key), and 

 there is no evidence, so far as I know, that these birds visit there (none 

 remains over night on the small islands belonging to the Tortugas group). 

 On page 194 it is shown that in all probability these birds do not leave the 

 island for distances greater than 15 knots in their search for food, and 

 that thev return at nightfall (or shortly thereafter) and leave at daybreak. 

 My exi^lanation of this failure to " shift the watch " is found in the peculiar 

 restless nature of the birds. In actually observing their behavior during 

 the shifts which occurred toward nightfall, I found that R would come and 

 push aside. would leave for a few moments, then would return and 

 scrouge back upon the nest. This would, sometimes be repeated three or 

 four times, one bird leaving the other temporarily in possession of the nest. 

 If this procedure were gone through with in the early morning hours, it is 

 easy to see how the wrong bird might easily join a group of other sooties 

 leaving the island for food. O would thus be left in possession of the 

 nest for two days in succession. The settlement of this point is one ex- 

 tremely to be desired. If later controlled experimentation is ever to be 

 undertaken, it is necessary for us thoroughly to understand their feeding 

 and nesting habits.' 



Occasionally my records show the presence of both birds at the nest for 

 several hours at a time. The general behavior of the brooding birds can 

 best be understood by citations from my notes, which were made at the time 

 and place of observation. By the following citations I hope to give a general 

 impression of the behavior of the sooty colony at a time when its life is most 

 complex, about the middle of May. Some of the birds have laid and are 

 brooding their eggs, while others have not yet laid, but are present defending 

 the nest-sites. In order to facilitate description, I shall use the letter .S" to 

 designate the bird brooding the egg (the " sitter ") and G to designate the 

 mate of this bird, which is usually standing guard (when present). The 

 term " layers " is used to designate those birds which have chosen a nest-site 

 but have not yet laid the (one) egg. Reference to the habits of the latter 

 should more properly have been made on page 203, but since the behavior 

 of the " layers " influences the behavior of the brooding birds to some ex- 

 tent they enter into the observation. 



Mav 13, 1907. Position taken near large group of " layers " and " sit- 

 ters." The S"s droop their wings and waddle around the egg. finally sitting 

 down upon it in a stiff and clunisy fashion. They are very much more rest- 

 less than the noddies. They are' constantly engaging in fights, leaving the 

 eggs in order to do so. They turn round and round frequently, orienting the 

 head differently at each adjustment. In some cases the G is present. In one 



' It is suggested that the nesting behavior at night could be studied by means 

 of flashlight photographs if the birds and nests were prominently enough marked. 

 Fig. 21, plate ", shows poorlj' the possibilities in this method. 



