124 BtTLLETlN 121, UNITED STATES NATIONAL MUSEUM. 



The second day on the island Mr. James M. Gaylord, the botanist of our 

 party, reported finding a " half-grown petrel incubating an egg " on another 

 part of the island. Scarcely daring to hope, but suspecting that it might be the 

 almost mythical least petrel, he was instructed to bring it back with him when 

 he returned from that quarter next day. As we had surmised, the specimen 

 proved to be Halocyptena microsoma, which we subsequently found breeding 

 in several parts of the island. All eggs of this species were taken either 

 from under loose slabs of rock or crevices in the broken ledges, the former 

 location seeming to be preferred. None were found in burrows, although 

 several were opened in the colonies of this species. They all contained either 

 0. melania or 0. socorroensis. 



Eggs taken from July 24 to 27 were in most cases fresh or but slightly 

 incubated, though many were well advanced in incubation. 



Downy young, and even incubated eggs were found on our return to the 

 island September 8. 



Again he (1900«) says: 



In a rock wall about seven feet long and less than two feet high, I once 

 found twenty-eight of these little petrels, but I have never found them in other 

 islands of the coast. 



Eggs. — The Q,gg of the least petrel is well described by Mr. Anthony 

 (1896a), as follows: 



In shape the eggs of the least petrel were more inclined to be elliptical than 

 either of the other species described, but were often elongate-ovate, short or 

 even in some cases rounded ovate, as in the species of Oceanodroma. 



They were pure white, with rosy flush before being blown, but dead white 

 afterward. In many, if not in the majority of our specimens, a ring of very 

 minute black specks encircled one or both ends. These specks came off upon 

 the slightest touch, leaving slight stains or marks such as might be madte by 

 brushing away a spot of lampblack which had accidentally fallen on the shell. 



Ten eggs of this species averaged in measurement 29.4 by 19.3 millimeters. 



The measurements of 40 eggs, in various collections, average 23.4 

 by 19.4 millimeters; the eggs showing the four extremes measure 

 28.2 by 22, 23 by 18.5, and 25.2 by 18 millimeters. 



Young. — Mr. Anthony (18985) says, of the downy young: 



Young were taken as late as September 7 or 8 that were but a few days old. 

 They were like the young of the three species of Oceanodroma I have mentioned, 

 except for size. All are covered with sooty or slaty black down, through which 

 the feathers appear when the bird is nearly or quite fully grown. 



Behavior. — The same writer (1900a) gives an interesting account 

 of the peculiar notes of the least petrel, which I quote in full, as 

 follows : 



As soon as the rocky ground at the base of the hills is reached, a strange note 

 is heard, which seems to come from the loose rocks fallen from a small ledge 

 above, and resembles the " whirring " of a rapidly revolving cog wheel. For 

 about ten seconds the whizzing continues, when suddenly a note is dropped — 

 there is a quick gasp, as for breath — and instantly the wheels begin to revolve 

 again, having given one the impression that there is a broken cog in the buried 

 machine. I have no idea how long the strange note might be continued. I have 



