302 



REVIEW OF JAPANESE BIRDS. 

 II.— Measurements o/Demiegretta jugularis. 



15296 

 15298 

 15281 

 15288 

 17102 



Locality. 



Samoan Lslanda • 



Upolu Islands 



Aurora Island. Society Islands 



Matavai Bay, Tahiti, Society Lslands 

 Tongatabu Island 



300 

 284 

 286 

 293 

 303 



102 

 89 

 95 

 92 

 95 





92 



Demiegretta greyi (Gray). 

 White Reef Heron. 



ISi'i.—ncrodias greyi Gray, List B. Brit. Mits., Ill, p. 80 {part; nomen nudum). 

 18id.—Herodias grnji GotTLD, B. Austr.,VI, p. & pi. 61 (clescr. & fig. ).—Ardca g. Cassin, 



Proc. Acad. Phila., 1802, p. 321. 

 187 i.— Demiegretta Candida Tytler, Stray Featli., II, p. 307. 

 1377.— Ardea jngularis var. greyi ReichexOW, Jouru. f. Orn., 1877, p. 2C2. 

 1^7.— Ardea grayi Seeboiim, Ihis, 1887, p. 182 (uec Sykes). 



A perfectly white Reef Heron, obtained by Mr. Stiiupson during bis 

 visit to Liu Kiu in December, 1854, forces upon us the very perplex- 

 ing question of the so-called "dichromatism" in the Herons. As this 

 problem has not previously entered Japanese ornithology a brief review 

 of it may not be out of place. 



By the term "dichromatism" we designate the peculiarity in certain 

 species of birds, that individuals, otherwise identical, present two dif- 

 ferent styles of coloration, or "phases," presumably more or less inde- 

 pendent of geographical distribution, present or past, or, in fact, of any 

 apparent cause whatsoever. The difBculty in finding a plausible theory 

 is much increased by the circumstance that there are nearly as many 

 kinds of dichromatism as there are dichromatic species. Thus, among 

 Japanese birds we may mention Richardson's Jaeger {Sfercorarius par- 

 asiticus), the Fulmar {Fulmarus), and the little Screech Owl {Megascops 

 japonicus), but in neither of these cases do we know the exact nature 

 of the phenomenon nor its significance in the animal economy. In some 

 of the ca^es, however, we can trace a connection with the geographical 

 distribution, but the only tbing we know for certain is, that the two 

 phases are entirely independent of sex, age, or season. 



The Herons afford a more striking and at the same time more puzzling 

 example of dichromatism, for of the two phases one is generally very 

 vividly colored or strongly marked, while the other is pure white all 

 over. This problem has been studied closer here in America than in 

 the Old World, and consequently we know a little more about the 

 American si)ecies. The earlier authors supposed that the white birds 

 were the young ones, but observations both in the Old World and in 

 this hemisphere have proved conclusively that this was an entirely 



