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 have 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.) 
