Life-Histories of the Booby and the Mau-o'-lVar Bird. 147 



in connection with the high percentage of infertihty, we attribute the dis- 

 crepancy between the number of eggs laid and the number of young reared. 



Our studies were not sufficiently prolonged to enable us to determine 

 whether, when both eggs were fertile, the young first hatched survived or 

 whether, through continued incubation of the remaining egg, it starved and the 

 young hatched from the last-laid egg lived ; but in one instance a nest was 

 observed containing a lately hatched dead young and an egg with an embryo. 



The case is unique among birds, as far as I am aware, but that the data 

 on Cay Verde do not reveal an exceptional condition is apparently proven 

 by the observations of Walter K. Fisher^ in the Leeward Islands of the 

 Hawaiian group, where both Siila cyaitops and 5". leucoijastra were found 

 to lay 2 eggs and rear but i young. 



The young booby is born practically naked, and since exposure to the sun 

 before the downy plumage is developed would result fatally, it is constantly 

 brooded, one parent immediately replacing the other when the brooding bird 

 is relieved. Brooding continues even when the white down is well developed 

 and the young bird, then too large to be wholly covered by the parent, lies 

 flat on the ground, the head exposed, the eyes closed, apparently dead. This 

 relaxed attitude is also taken by young which are not sheltered by the parent, 

 and we were not a little surprised on several occasions, when about to ex- 

 amine an evidently dead bird, to have it jump up and with a trumpeting 

 call blare at us with open mouth. Nor do they rely only on the voice for 

 defense, but use the bill effectively, and, as has been remarked, they possess 

 with the adult the somewhat ludicrous habit of venting their feelings by 

 picking up bits of stick and grass. 



Compared with other rookeries I have visited, the mortality among 

 young boobies on Cay Verde — aside from the prenatal mortality already 

 referred to — was surprisingly small. This I attribute to the isolation of the 

 cay, which permits the birds to rear their young with little or no intrusion 

 by man, whose presence, even as a visitor, results in great confusion and 

 consequent death among the young of ground-nesting colonial birds. 



The young were fed on squids and fishes, which in a more or less di- 

 gested condition they obtained by thrusting their heads and necks down the 

 parent's throat, a manner of feeding common to all the Steganopodes with 

 whose habits I am familiar (including Pelecanns, Fregata, Phalacrocorax, 

 and Anhinga). I have not. however, seen PInicthon feeding its voung, and 

 it would be interesting to know whether this tern-like member of the order 

 has a similar method of administering food. 



Evidently but one brood is reared, since approximately 3 months must 

 elapse after the egg is laid before the young can fly and care for itself. 



' Birds of Laysan and the Leeward Islands, Hawaiian Group, U. S. Fish Comm. 

 Bull.. 1003, pp. 28-30. 



