92 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



I have never seen the adults dive, but I once saw an imma- 

 ture bird do so. It shot obHquely into the water from a dis- 

 tance of only a few feet, entering at a very small angle and 

 making a semicircle while in the water. It came up facing 

 in the direction just opposite to that in which it entered. One 

 day I saw one sitting on the water with head immersed for a 

 long time, and apparently looking for food. Fish seem to con- 

 stitute their chief diet. Once I saw a Peruvian Booby at- 

 tack a wounded Blue-footed Booby and force it to disgorge. 

 On another occasion I saw one catch a flying-fish by skim- 

 ming close over the water after it. 



The colors of the naked parts of the adults in life were as 

 follows : Bill vinaceous-pink, shading into ochre-yellow at tip 

 and along tomia; gular sac slate-gray; iris gamboge-yellow; 

 feet dark olive-buff. 



An immature bird shot at Cormorant Bay, Charles Island, 

 on May 17, had an olive-buff bill; the gular sac and feet were 

 of about the same color as those of adults. Gular sacs of 

 young in down were flesh-colored. In fully fledged young 

 they were dark blue or blackish blue. 



Although the Academy's series of skins of this species num- 

 bers sixty-nine, and is well supplied with birds both in juvenal 

 plumage and in adult plumage, specimens are lacking to show 

 the complete transition from juvenal to adult. One speci- 

 men, No. 2478, taken on October 12, 1906, in latitude 15° 40' 

 North, longitude 110° 12' West, is apparently just completing 

 the assumption of the adult plumage, for a number of partially 

 dusky feathers are still to be seen in the upper parts. 



An examination of the adult males in the collection revealed 

 birds with new outer primaries appearing, as follows : From 

 Hood Island in June and October ; from Culpepper in Septem- 

 ber. Only one female (No. 2510) was found in a like condi- 

 tion — an individual taken on Hood on October 2. In most 

 cases the males seemed to be somewhat in advance of the 

 females in the progress of the moult. 



In conjunction with the measurements of twenty-three adult 

 males and twenty-five adult females, there are given for the 

 sake of comparison, in Table XI, p. 117, the measurements of 

 seven adult males and six adult females of Sula cyanops. The 

 average Sula variegata has a decidedly longer wing, and has 



