LIFE HISTORIES OF NORTH AMERICAN PETRELS AND PELICANS. 203 



semicircles backed by water-worn cliffs on the landward side and floored 

 with sand and huge rocks fallen from the overhang above. The thin soil of 

 the island supports a considerable growtli of vegetation, bound with thorny 

 creepers into an impassable jungle, with only small grass-grown openings 

 offering a pathway. The West Indian birch (Bursera simaruJ)ci), with its 

 trunk and limbs curiously shortened, thickened and gnarled in the struggle 

 for life, is the common tree, while growths of three species of cactuses are 

 common. 



On this interesting island, boasting of but eleven i-esident avine forms, the 

 booby (Sula leucogastra) has chosen its home and here in June, 1012, I spent 

 a few days in studying the habits of these ungainly birds. Between eight and 

 ten thousand of them at a conservative estimate occupied the rookeries, spread 

 over the entire island, but they were so distributed on the steep brush-covered 

 slopes that a more accurate census was impracticable. Though they were seen 

 at the top of the higher of the two hills, the greater number were found within 

 four hundred feet of the beach, gathered usually in groups. By my fishermen 

 they were said to nest from late June until October, but these dates are very 

 uncertain. The young now were nearly all caring for themselves, though 

 a few showed traces of down feathers clinging to the tips of the feathers 

 about the head, and I would consider February or March a more probable date 

 for their nesting. A few were seen playing with sticks and straws as though 

 contemplating nest building, but the sexual organs of those taken were little 

 developed. Birds in all possible intermediate plumages were seen and im- 

 mature specimens were mucli more common than the fully adult with smooth 

 dark brown heads and white underparts. 



The young birds were averse to flying when they could avoid it, but pre- 

 ferred to scramble away under the bushes awkwardly, falling over sticks and 

 stones in their haste. Even the adults could not take flight from a level sur- 

 face, but had to launch themselves from the cliffs and sail down for a dis- 

 tance before being able to rise with strong wing beats. From the limbs of 

 the trees they flew readily, but on the ground I captured several by merely 

 pinning them down with my gun barrel. They showed little real fear of me 

 and many stood their ground, snapping and hissing, and it was a point of 

 wisdom to keep beyond reach of their sharp powerful beaks. It rather gave 

 me the shivers occasionally to see one flounder and flop through and over a 

 bed of prickly pear, but the birds seemed careless of the thorns. Numbers 

 were seen with spines or even small lobes of cactus hanging to the feet or 

 wings, and the dissemination of the plants by this means can be readily pic- 

 tured. At a gunshot there was a great rush among those near by, and the air 

 for a few minutes would be filled with them circling and crossing, frequently 

 almost within reach. The confusion among them would cease gradually, and 

 they would soon be all around again, eyeing me curiously or forgetful of my 

 presence, busy with their own aft'airs. On the rough limestone blocks above 

 the sea they sat in rows in the blazing sun, rather upright, occasionally 

 waddling along a foot or two, but usually motionless. Birds came and went 

 during the day, flying out to sea to feed, sometimes at considerable distances 

 off shore, but they were most active in the morning and evening. The com- 

 mon call note was a loud quack quack quack, and at night, whenever I awoke, 

 there was always much commotion among them. 



Eggs. — From the foregoing quotations it would seem as if two 

 eggs was the normal set with the common booby, but apparently 

 sometimes only one is laid. The eggs vary considerably in shape 



