476 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 56. 



spacing of the nests (as shown in pi. 63, fig. 2) being practically 

 invariable and determined apparently by the minimum space require- 

 ments of a pair of breeding birds. One may safely compute the 

 number of breeding adults by multiplying by 6 the number of square 

 meters covered by the aggregation. 



At this time, the close of the breeding season, the immature but 

 grown nestlings were still being fed by the parents from mouth to 

 mouth and occupied the parental nest. Estimating on the basis of 

 two birds to the nest and three nests to the square meter, there would 

 be 360,000 parent birds in the flock, with undoubtedly an equal or 

 greater number of unmature birds able to fly, about three-quarters 

 of a million birds in all.^ I had the opportunity to revisit this island 

 briefly in the following month of July to find the flock at least 50 

 per cent larger, practically the entire island being occupied. The 

 increase in size of the flock m this brief time may have been due in 

 part to the accession of birds from the Ballestas Islands, but un- 

 doubtedly in part a natural expansion, as the older birds of the past 

 season's brood mated and established homes of their own. 



The photograph shows the form and arrangement of the nests on 

 the hillside (pi. 63, fig. 2). The nests are rather less regular in dis- 

 tribution than at first appears. Whatever may have been the origin 

 of the nests, they were now composed entirely of guano except for 

 the little gravel or stone which was mixed with the guano. Each 

 nest is like a shallow basin with heavy rolled rim, the diameter of the 

 hollow of the basin being 20 cm. (8 inches) and that of the circum- 

 ference of the rim 40 cm. (16 inches); the raised ring of guano sur- 

 rounding the hollow is then about 4 inches wide. The nests, how- 

 ever, are not separate, but are portions of the continuous carpet of 

 guano. The distance from center to center of nests varies from 50 

 to 70 cm., being generally a little less than 60 cm. 



The young birds in the early days of June, although able to fly 

 from the island with the older birds, were continuaUy seen to be 

 nagging the parents for food, pecking at them and expanding the 

 throat to form a receptive pouch. When the food is conveyed the 

 head of the young disappears entirely down the long throat of the 

 parent and the two bend over to one side or the other, the brother 

 young bird meantime making every effort to inteifere and displace 

 the more fortunate nestling. Even at this time there were among 

 mature birds suggestions of preliminary love plays in the raising 

 and lowering of crests and the brushing together of the birds of a 

 pair. It was several weeks later v/hen this island was revisited (in 



1 1 am aware that others have estimated the number of cormorants at this island at much higher 

 figures — up to 10,000,000; in the absence, however, of precise data regarding the method of computation 

 employed, such estimates are to be viewed with conser\'atism at least. 



