96 ALBINISM 



1900, p. 108). On the other hand, there seems better ground for belief 

 in the theory, advanced by Dr. C. Hart Merriam, that these so-called 

 banner marks protect their possessors by being so strikingly evident 

 when their wearers are in flight that their sudden and complete efface- 

 ment when the creature takes to cover, tends to puzzle the pursuer, 

 which, looking in vain for a victim conspicuously marked with white, 

 soon abandons the chase. 



The subject is a fascinating one and is to be especially commended to 

 field students, who alone can supply the data on which a solution of 

 the problems involved can be based. 



Albinism. Albinism is not infrequent among birds and may occur 

 in any species. I hare seen a white Crow and a white Turkey Vulture. 

 It is, however, rarely complete but more frequently affects a part of the 

 plumage, when it is usually symmetrical, that is, if a feather in one wing 

 be white the corresponding feather in the other wing will also be white; 



The presence of an albino bird always excites interest. When, be- 

 cause of its markings, the history of the individual may be learned, and 

 possibly its return to a certain locality noted year after year, albinism 

 permits of the making of observations of real value. But albinism in 

 itself is a matter calling for no special record or comment. It is due to 

 an absence of pigment in the part affected and may indicate a more or 

 less degenerate condition in the individual exhibiting it. Albinistic 

 English Sparrows are not uncommon, a fact which may be due to the 

 abundance of the species and ease with which it is observed, or to exces- 

 sive inbreeding among a comparatively limited number of very local 

 individuals. 



Melanism, or undue blackness, implies an excess of pigment, while 

 xanthochroism and erythrism are terms applied respectively to ab- 

 normally yellow or red birds. These three phases of color are, as a rule, 

 shown only in caged-birds and are then evidently due to unnatural 

 diet or other conditions. (See Beebe, '07.) 



Dichromatism. Dichromatism implies the existence of two phases 

 of color in the same species. It is well illustrated by our Screech Owl, 

 some individuals of which are gray and others rufous. (See frontispiece.) 

 This difference in color is not dependent upon age, sex or season; indeed, 

 gray and rufous birds may be found in the same family. It appears, 

 however, to be connected with locality, since a species may be dichro- 

 matic in one part of its range and less so or not at all in another part 

 of its range. The rufous phase of the Screech Owl, for example, is rare 

 in Florida, just as the black phase of the gray squirrel is rare in Florida. 

 Beyond this relation between dichromatism and locality its causes are 

 not understood. 



SUGGESTIONS FOR THE STUDENT 



The processes of molt and feather-growth may be studied in captive 

 birds provided they be kept under proper conditions. Change in conditions 

 may advance or retard molt. (See Beebe, '08.) 



