232 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



Mr. Moore who, as I have said, is a maa of great observation, brings 

 another interesting evidence of the unity of species in these two forms. 

 He has noticed that where a number of herons are feeding in the same 

 waters each will tolerate the near presence of other birds, provided they 

 are all of different species. The Great White Egret, the Great Blue 

 Heron, the Little Blue, the Snowy and others will all peacefully feed 

 side by side, but let another bird of any one of the same species come 

 and immediately its own near relative, will at once attack it and drive 

 it away to a respectful distance. No heron will permit, when feeding, 

 the near presence of one of its own species. Tried by this test, the Blue 

 and Brown Egrets and White Egrets belong to the same family, for no 

 one of either of these birds will suffer the near presence, when it is feed- 

 ing, of either of these two forms, whether white or blue. 



" This then appears to be the present explanation of facts that have 

 appeared so inconsistent and contradictory. We need not presume that 

 Audubon was imposed upon, still less that he sought to impose upon us. 

 We can accept Dr. Gambel's facts as well as Mr. Audubon's, and believe 

 in the truth of both. But we are not yet enabled to say what signifi- 

 cance, if any, these different colors possess. It remains as great a puz- 

 zle in this respect as ever. 



" Yet it is not wholly unexampled. Our common Screech Owl, 8. asio, 

 appears in two very different styles of plumage. Some are red and some 

 are brown. It was once supposed to be significant of age. The red 

 plumage was regarded as the young, and the brown as the color of the 

 mature bird. Audubon so figures them. Our good friend. Dr. Sam 

 Cabot, in his younger days shot an old bird in the red plumage, feeding 

 some young in the ashy brown dress, and he naturally concluded that 

 Audubon had put the horse where the cart ought to go. But others, 

 who had different experience, would not accept his conclusions. At 

 length it was discovered that in one sense both were right, and in 

 another that both were wrong. Old birds are both red and brown, and 

 young birds are both brown and red, and both are of the same species, 

 the color having no significance that we can as yet determine." 



Mr. Moore's observations, as stated abuve, afford conclusive evidence 

 that Ardea rufa and A. pealei Bonap. are one and the same species. 

 That these two distinct phases represent a sort of dichromatism analo- 

 gous to that of the little Screech Owl, but differing in that the depart- 

 ure from the normal coloration exhibits itself in another color (pure 

 white instead of rufous), I consider unquestionable. This kind of 

 dichromatism appears to be nearly if not quite peculiar to the Heron 

 tribe (I can recall no instance among other birds), and is characteristic 

 of several species, among which, besides the present one, are Demiegretta 

 sacra (Gmel.) of India, Australia, etc., Florida eceritlea (Linn.), and, as 

 I think is quite capable of demonstration, Ardea occidentalis Aud. 



