146 Papers from the Marine Biologieal Laboratory at Tortugas. 



In spite of the apparent sociabilit}- expressed hy their communal habits, 

 the boobies immediately resented trespass on their home site by one of their 

 own kind. Where the nature of the ground permitted, their nests were 

 placed with more or less regularity 6 to 8 feet from one another. As long 

 as a bird remained within its own domain, having a diameter of approxi- 

 mately 6 to 8 feet, it was not molested ; but let it or its young advance be- 

 yond these limits and they were promptly attacked. 



So closely, however, are the birds confined to their own little areas that 

 difficulties of this kind are rare, and under normal conditions peace reigns 

 in the rookery. But when, as we walked through the rookery, the birds in 

 escaping from the larger evil forgot the lesser one and inadvertently backed 

 on to a neighbor's territory, the unusual cause of the trespass was not ac- 

 cepted as an excuse and they found the " frying-])an " worse than the " fire," 

 as the enraged owner, with bristling feathers, furiously assailed them with 

 open bill, sometimes taking hold. At these times, and whenever the birds 

 were alarmed, they gave utterance to hoarse, raucous screams or screeches, 

 though as a rule they were comparatively silent. 



THE NEST. 



The booby's nests on Cay Verde were usually slight hollows in the 

 ground, with often a scanty lining or rim of dried grasses, but in some in- 

 stances even this humble preparation for housekeeping was lacking, and 

 the eggs were laid without pretence of nest. 



EGGS .\ND YOUNG. 



About 98 per cent of the boobies nesting on Cay Verde had young, some 

 of which were newly hatched, while a few were on the wing, but the largest 

 number were beginning to acquire flight feathers. Of the nests, 35 contained 

 eggs, of which 21 held 2 eggs, while in 14 there was but I ; but possibly in 

 some, if not most of these, another egg would have been laid. As a rule, 

 therefore, there were 2 eggs, this confirming previously recorded observa- 

 tions on the nesting habits of this species. ( )n the other hand, 2 young were 

 the exception. C)f 740 nests counted by Dr. Mayer on the east side of the 

 cay, only 2 contained young, and both pairs were well grown and approxi- 

 mately the same size. 



Examination of the eggs contained in sets of two showed that either 

 there was a marked difference in the development of the embryos or that one 

 or both eggs were infertile. For example, of 13 nests containing 2 eggs, in 

 3 nests both were bad ; in 10 both were good, but with every good pair there 

 was about a week's difference in the age of the embryo. In 6 nests each con- 

 taining one young and one egg, 5 of the eggs were decomposed. 



With those boobies w-hich lay 2 eggs, apparently a week intervenes be- 

 tween the laying of the first and second egg, and to this unusual irregularity, 



