348 



Recent Literature. Q " t 



Mr. Hasbrouck divides his paper into two parts: I. 'Relationship of 

 Dichromatism to Evolution'; II. 'Causes and Influences.' In Part I, after 

 giving a history of the views formerly held by ornithologists as to whether 

 the red and gray phases were distinct species or merely two forms of the 

 same species, the author takes up the subject of the geographical distribu- 

 tion of these two color phases*, and the "relation of dichromatism to evolu- 

 tion" in the Screech Owl group. In regard to the distribution and 

 evolution of the two phases and of the intermediate stages, he finds that 

 "dichromatism is principally confined to the typical form of Megascops 

 asio, appearing but slightly in the Florida form (Megascops a. Jlorid<ui us) , 

 and barely reaching the Texan subspecies, mccallii" the western and 

 southwestern forms of the group "remaining true to their normal color." 

 He attempts to show, "first, that while the red, the gray and the inter- 

 mediate phases are at present but individual variations of the same species 

 — the grav was the ancestral stock; second, that from the gray bird has 

 evolved the red, which at some future time will be recognized as a sub- 

 species with a range peculiar to itself, and thus dichromatism is one step 

 in the evolution of the Screech Owl, while the various phases exhibited are 

 the transitorial stages of development of one species into another ; third, 

 that this condition of affairs is influenced by four powerful factors," two of 

 which are temperature and humidity, "the most potent of which is tem- 

 perature; fourth, that the predominating distribution is largely confined to 

 the faunal divisions of the eastern United States, and as such is approach- 

 ing the subspecific differentiation of the two phases; lastly, that the 

 Darwinian theory of 'Reproduction with variation and the survival of the 

 fittest,' is well exemplified in our common little Megascops asio." 



In support of these various propositions he presents data to show that the 

 gray phase is the only form along the northern border of the range of the 

 species, and that its distribution about coincides with the boundaries of the 

 Canadian Fauna, except that it turns abruptly southward in Minnesota and 

 extends down to Middle Kansas. Below this is a somewhat similar belt 

 where mixed birds occur with the gray phase predominant; while below 

 this red birds prevail nearly to the Gulf Coast, where gray birds again 

 begin to predominate and finally gray only occur over most of Florida. 

 Red birds alone appear to be found about Washington, and over quite 

 a belt along the Mississippi River, from about the mouth of the Missouri 

 to the mouth of the Arkansas. An examination of his table of localities 

 on which his generalizations, as graphically represented on his Map II, are 

 based, however, shows that the observations are far too scanty to render it 

 at all certain that these sweeping conclusions are well grounded. For 

 instance, only one to three localities are mentioned respectively for such 

 large areas as Alabama, Arkansas, Connecticut, Georgia, Maine, Michi- 

 '4111, Minnesota, Mississippi, Nebraska, New Hampshire, New Brunswick, 

 South Carolina, and Tennessee. The whole number of localities is only 

 120, and in several instances quite a number of them are included within 

 comparatively small areas. This shows how slender is the basis for a 



