BIRDS OF THE TRES MARIAS ISLANDS. 29 



and would have been overlooked but for the angry cries of the old 

 bird when she heard me walking over the roof of her habitation. "At, 

 sunrise the old birds were found sitting side by side at the mouths of 

 their nesting places waiting to enjoy the first rays of sunlight. Half 

 an hour later one of each pair started out to sea while the other resumed 

 its place on the nest. When disturbed on the nest their cries are very 

 shrill and strident, consisting of a series of short, harsh, clicking or 

 rattling sounds something like the noise of an old-fashioned watch- 

 man's rattle. The young are covered at first with fluffy white down. 

 Before they are one-third grown the first plumage begins to appear, 

 and is very similar to that of the adults, except that the black barring 

 on the back is broader. 



Sula websteri Rothschild. Webster's Booby. 



Sula bassana Grayson, Proc. Boston Soc. Nat. Hist., p. 302, 1871. 



Sula websteri Rothschild, Bull. Brit. Orn. Club, VII, No. LIV, p. LII, 1898. 



This booby is no doubt the Sula bassana reported from Isabel Island 

 by Grayson but not seen by us. Mr. Anthony found it the most abun- 

 dant species breeding on the Revillagigedo Islands during the summer 

 of 1898. 



Sula brewsteri Goss. Brewster's Booby. 

 Sula brewsteri Goss, Auk V, p. 242, 1888. 



Brewster's boobies were very numerous on a small hill at one side 

 of the little bay where we lauded on Isabel Island April 22, but there 

 were no signs of their breeding. They came in from sea during the 

 first half of the afternoon and sat about on rocky parts of the shore 

 until nightfall. Scattered individuals were also seen about the ledges 

 and tops of the cliffs facing the sea. T.he following morning at day- 

 break they were congregated on the little hill already mentioned which 

 is probably their regular roosting place. About half an hour after 

 sunrise they began to start out to sea singly and by twos and threes 

 until all were off on the day's fishing expedition. A few were seen 

 about the rocks just oft' San Bias, and were said to breed on the large 

 rock (Piedra Blanca) midway between Isabel and San Bias. Only a 

 few of these boobies were seen about the Tres Marias until an islet 

 was visited off the northwest shore of Maria Cleofa. This islet rises 

 from 150 to 200 feet above the sea, with cliffs on all sides. The sum- 

 mit is mainly rolling, with an elevated, sloping bench on one end At 

 this time, May 30, many thousands of boobies were breeding on the bare 

 top of this rock. The eggs were laid directly on the surface, with no 

 sign of a nest. The sun was intensely hot and heated the rocks so that 

 they were uncomfortably warm to the touch. The birds did not sit 

 upon the eggs during the hottest hours, but while standing to avoid 

 contact with the heated rocks kept in such position that the eggs or 

 young were shaded from the sun, and thus had their vitality preserved. 

 While trying to secure photographs of this breeding ground a few of 

 the old birds flew away and it was surprising to see how quickly the 



