194 BULLETIN 121, UNITED STATES NATIONAL MUSEUM. 



Nest'mg. — Dr. Walter K. Fisher (1906) has given us the following 

 account of the nesting habits of this species on Laysan Island : 



On Laysan the masked, or blue-faced booby lives only on the sedgy slope 

 facing the ocean, exposed to spray-laden winds and close to the booming surf. 

 On the inner slopes of the island the species is entirely absent, being replaced 

 by its somewhat smaller congener Sula piscator. We found cyanops most 

 plentiful on the northeast, east, and southern exposures, where the narrow 

 littoral slope is broadest, but on the west side, where a little bluff replaces the 

 seaward slope, the birds are absent. The homes of these boobies are not 

 crowded, but are scattered here and there over the greensward and from a dis- 

 tance are easily recognized by a little round patch of sand and the sentinel 

 bird. Two limy, white eggs are laid on the bare sand, with usually no sem- 

 blance of a nest, or occasionally there may be a little dried sedge scratched 

 about the eggs or young. 



Dr. Thomas H. Streets found this booby breeding on Christmas 

 Island, though not very abundantly. He says (1877) : "They build 

 no nest, but scratch a slight concavity in the fine coral sand, where 

 the egg is deposited." He speaks, however, of a nest he found on 

 Palmyra Island, which " was well constructed of grass." 



Mr. A. W. Anthony (1898/) writes of their nesting habits in the 

 Eevillagigedo Islands as follows: 



On May 19 we found some colonies of blue-faced boobys on Clarion Island, in 

 which there were fresh eggs and young birds, and even a few well-grown young 

 were seen. The nests were mere hollows in the coral sand, anywhere from just 

 above high tide to the top of the island, at 500 feet altitude. The nests were 

 all vigorously defended by the birds, who greeted our approach with deafening 

 shrieks and threatening bills. Indeed, their bill is not to be despised. It is 

 as sharp as a bayonet and is wielded with no little force, as my shins could 

 testify after an hour's collecting among the nests. If the Webster boobys re- 

 quired a kick to drive them from their nests, the blue-faced required a charge 

 of dynamite. I have repeatedly put my foot under a sitting bird — gently to 

 save the eggs— and thrown her as far as I could — with vigor to save my shins — 

 but before I could grab the eggs, was driven back by a shrieking demon in 

 snowy white that charged at me with agility surprising in so large a bird. On 

 one occasion a bird came in from out at sea and with a scream threw itself 

 between me and a sitting bird I was approaching, constantly moving about so 

 as to interpose its body between its nest and the threatening danger. The de- 

 fense being so spirited and gallant I concluded that the eggs were far ad- 

 vanced in incubation. 



I several times found the present species sitting on large sea shells, which 

 in shape and size somewhat resembled their eggs. The " boobies " seemed per- 

 fectly contented with the substitute, and I often supplied them with the 

 shells after taking their eggs. These they immediately tucked under their 

 breasts with their bills, and accepted the change as a matter of course. One 

 nest, from which I took one egg, was supplied with two shells. Both were 

 tucked away, but next day I found that one had been discarded. Others which 

 were incubating two eggs accepted two shells in exchange and were sitting on 

 them ten days later, when we left the island. 



Eggs. — The set generally consists of two eggs, though sometimes 

 only one. The shape varies from ovate to elongate oval or short fusi- 



