88 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser, 



rise and fall that characterizes the flight of other members of 

 this genus. The wing-strokes occur on the rise ; on the down- 

 ward swing the bird sails, in calm weather often going sev- 

 eral yards very close to the surface of the water. The mem- 

 bers of a flock are practically synchronous in every action. 



In fishing, the Red-footed Booby pursues the same tactics as 

 the Blue-footed, diving, with wings half closed and rigid, 

 from a height of twenty or thirty feet. On one occasion, how- 

 ever, I saw one catching flying-fish on the wing by swooping 

 into schools which were skimming along above the water. 



Over half of the Academy's series of fifty-eight skins is 

 made up of adult birds. Some of these, in the dark phase, 

 show new dusky feathers replacing old, faded, dusky feathers. 



In No. 2440 (male, dark phase, from Cocos), the bill has 

 dried of a bright-red color. This bird has the black gular sac 

 and is evidently adult. In most cases the bill dries mainly of 

 a dusky bluish black. 



The colors of the naked parts of a freshly-killed adult dark- 

 phase bird were as follows: Bill pale blue, except at base, 

 where it was peach-blossom pink ; skin around eyes azure blue ; 

 gular sac black ; feet poppy-red. 



The colors of the naked parts of a freshly-killed brown- 

 plumaged immature bird were as follows : Bill brownish with 

 pinkish blotches near base; skin around eyes dark blue; gular 

 sac French-gray, blackish at posterior edge; feet dull pinkish 

 with dirty bluish shade in webs. 



The colors of the naked parts of a freshly-killed immature 

 bird with pale under parts were as follows : Bill pale bluish 

 and pinkish with dark tip; skin around eyes blue; gular sac 

 pale blue with black along sides next the mandibular rami; 

 feet pinkish vinaceous. 



The single tgg taken at Cocos Island measures 58.7 mm. X 

 40.8 mm. It is dull chalky white in color. 



