426 University of California Publications in Zoology. |Vou.5 
central California, with an annual rainfall of but 25 inches, 
various deeply colored subspecies have differentiated. Here, 
however, there is a great preponderance of cloudy days. But it 
is clearly not a matter of actual precipitation. 
Neither does the influence of a humid atmosphere appear to 
be a direct cause of normal melanism, the experiments of Beebe 
to the contrary notwithstanding. (See Zoologica: Contributions 
of the New York Zool. Soe. I, 1907, pp. 1-41.) For the newly 
hatehed young and the young in newly acquired juvenal 
plumage show as great relative depth of coloring as the adults 
which have undergone many molts, and which have been for 
their lifetime bathed in the humid atmosphere. And further- 
more, dark-colored birds, members of “‘humid’’ faunas, in in- 
stances known to me remain for several generations imper- 
ceptibly changed when artificially transplanted into a relatively 
more arid climate, or when they have naturally extended their 
range beyond the confines of the humid faunal area in which 
they were with little doubt originally differentiated. 
As intitnated in the second paragraph preceding, the corre- 
lation of dark-colored species of birds with areas of excessive 
cloudiness, irrespective of rainfall, is so general as to demand 
serious consideration. Although an apparent fact, its signifi- 
cance is far from clear. Exposure to intense light from a 
cloudless sky (as with the human species and certain other 
animals) induces an increased deposit of dermal pigment. But 
in many others, the tone of coloration of the surroundings, 
whether black lava or white sand, appears to be assumed, irre- 
spective of the mean light intensity. It is held by some, and 
with good grounds if the matter is not pressed too far, that the 
tone of coloration of such birds as do not find it advantageous to 
be conspicuous, tends to harmonize exactly with the average or 
blended tone of the background, against which they ‘‘dis- 
appear’’ when motionless. This mean background varies in 
depth of tone directly with the percentage of cloudiness. This 
idea is upheld by the fact that the most typically dark-colored 
humid-belt birds are such as either regularly serve as prey or 
are predaceous; as the grouse, ptarmigan, fox and song spar- 
rows, juncos, thrushes, owls and certain hawks. Crows, ravens, 
