NATATORES. 



413 



that these and other species of this genus undergo very material 

 changes in the colors of their plumage, according, in all probability, 

 to season. We cannot, however, at present, give a precise or satis- 

 factory account of this supposed change in any one species, and we 

 have not, therefore, ventured to give the two birds now before us 

 otherwise than as distinct species. The birds of this genus, in our 

 opinion, require careful observation in their native localities, or inves- 

 tigation in such extended series of specimens as can be attained only 

 in time and with special attention. 



Under the head of the present species, Mr, Peale has the following 

 observations : 



" At the Island of Tahiti, on mountains elevated about six thousand 

 feet above the sea, this bird was found breeding in holes, in the month 

 of October. It is decidedly nocturnal in its habits, a few only being 

 now and then seen abroad in daylight. They sally forth from their 

 subterranean abodes about sunset to collect food for their young far 

 away at sea, being rarely found on the coast. 



" The specimen from which our drawing and description were taken 

 was procured by Mr. Dana, while on a most perilous excursion to the 

 summits of the volcanic peaks of the island. The natives who carried 

 it, finding its bite too severe, submitted it to a most cruel remedy, often 

 practised by the island bird-catchers, which is, to thrust the sharp point 

 of the upper mandible through the lower, thus yoking it with its own 

 jaw. In this state, it Avas kept until the party reached the coast. 



" On the tops of the same mountains, we saw a small species of 

 Petrel, resembling Thalassidroma oceanica, Bonaparte, Zool. Journal, 

 Vol. Ill, p. 89, but rather larger, with all the under parts white. It 

 appeared to have its nest there, though we did not succeed in finding 

 any, nor in obtaining specimens of the birds which were flying around 

 us, and when shot fell into the dense forests, thousands of feet below 

 us. 



" The background in the drawing, is from a sketch taken at the 

 only native settlement that we found in the interior, and represents 

 the peaks in which are the breeding-places of this and other oceanic 

 birds, high up on the River Popino." 



A single specimen only of this species is in the collection of the 

 Expedition. It is, apparently, in mature plumage, and is in good 

 condition. It is represented in our plate rather smaller than the 

 natural size. 



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