424 University of California Publications in Zoology. (Vou. 5 
contention is+based on the peculiar association of species which 
characterizes it, and upon the inelusion in it of several forms 
which appear to have differentiated within the region itself. 
MELANISM IN THE ENDEMIC SPECIES, 
A survey of the three faunas here discussed, to ascertain the 
general characters displayed by the respectively component 
species, Shows that, in the birds of the Sitkan and Prince Wil- 
liam Sound distriets as compared with corresponding species of 
the Yukon fauna, there is an increase in the extent of black 
markines and a darkening of the shades of brown and green, 
and a reduction in the general size, and disproportionate short- 
ening of the wings and tail. (See table on page 425.) 
The melanism referred to includes the most conspicuous 
specific and sub-specific characters of the birds (and many other 
terrestrial animals) of the coastal region of southeastern Alaska 
notorious for its heavy rainfall. This correlation of heavy pig- 
mentation with large precipitation, and vice versa, has been so 
generally observed and commented upon that the latter has 
often been advanced as a cause for the former. The correlation 
is an observed fact; but it is not yet acceptably explaimed, nor 
am I able to adduce any new evidence to solve the matter. A 
discussion of the present status of the problem may not prove 
out of place. 
The ‘‘humid coast belt’? of Alaska, as compared with the 
more arid interior, offers four obvious environmental conditions : 
(1) an extreme of precipitation—rainfall, heavy mists, fog; (2) 
a high relative humidity of the atmosphere when not actually 
saturated; (3) a very large percentage of cloudy days—that is, 
much shade; (4) impeded radiation and therefore a much more 
uniform temperature, free from the extremes of the arid region. 
That the melanism in question is caused by precipitation 
directly (although this is often assumed) appears to be abund- 
antly disproven by the occurrence of palely colored species in 
regions of great annual rainfall, as in the Sierra Nevada of 
California. Here the rain, averaging in places 70 inches per 
year, comes in brief, heavy storms interspersed with prolonged 
periods of clear weather. Furthermore, in the coastal region of 
