The Emu 



Official Organ of the Royal Australasian Ornithologists' Union 



Birds of a feather.' 



Vol. XXII. J 1st OCTOBER, 1922. [Part 2. 



On the Status of several species belonging to 



the two genera, Fregetta Bp. and Fregettornis 



Mathews 



By J. K. KIXGHORN, R.A.O.U., Zoologist, Australian 



Museum, and NEVILLE W. CAYLEY, R.A.O.U., 



Sydney. 



[By permission of the Trustees of the iVustralian Museum.] 



Introduction. 



The acquisition by the Australian Museum of several speci- 

 mens of Fregettornis from Lord Howe Is., led us to compare 

 them with others of the genus Fregetta, and to investigate the 

 status of several species belonging to both genera. Thorough 

 search permits us to include Fregetta melauogaster, F. tuhnlata 

 and F. leiicogaster, as synonyms of F. tropica, Gould, and we 

 have placed Fregettornis royanus, insularis, alisteri, and innomi- 

 natus under Fregettornis grallariits, Vieillot. Such a course may 

 at a glance seem rather drastic ; but on careful comparison of the 

 various descriptions, and examination of the volumes quoted in 

 the appended bibliography, we found no other course open 

 to us. 



Such slight colour-variation as exists between the several 

 species mentioned above is evidently due to some or all of the 

 following causes : — Firstly, according to Loomis^, no two birds 

 are exactly alike; a feature which is explained by the fact that 

 moulting in any species varies in different individuals, independ- 

 ent of their age, physical state, or time of breeding. Looniis 

 found that in many sj^ecies the breeding season was protracted 

 over a very large part of the year, not only in tropical, but in 

 temperate regions. Secondly, wear and tear of plumage through 

 fading and abrasion are so great in sea-birds that in the older 



