a 
Allen.] 1538.03 [April 17, 
called to a series of specimens of the Baltimore Oriole (Icterus balti- 
more), in which a transition was shown between specimens from Mas- 
sachusetts, (representing the average form of this species at the 
eastward) in which the lesser and middle coverts of the wing were bright 
orange, and others from middle Kansas, which had the lesser coverts, 
pale yellow, and the middle coverts white ; though specimens from east- 
ern Kansas had the lesser coverts of a deeper tint of yellow and 
the middle coverts of pale yellowish. In the Kansas speci- 
mens there was also much more white bordering the secondaries than 
in the usual eastern form. A series of sparrow-hawks (Falco spar- 
verius) was also shown, illustrating not only the differences in color 
between specimens from the Plains and others from Eastern North 
America, but also the transition from the northern form of F. spar- 
verius to the southern form described as F. sparveroides by Mr. N. A. 
Vigors, in 1820, from specimens from Cuba; although Ff’. sparveroides 
has ever since been generally regarded as a species satisfactorily dis- 
tinct from F. sparverius. In the northern form of F. sparverius a 
large rufous spot covers the greater part of the top of the head, 
which is entirely wanting in J’. sparveroides. In this form the colors 
generally are also darker, the axillaries having the black bars pre- 
dominating over the white ones, while the reverse of this obtains in 
the northern form. The specimens shown were chiefly from the Flor- 
ida Keys and other portions of South Florida, and exhibited a gradual 
reduction of the rufous spot on the crown to its entire disappearance, 
leaving the top of the head uniformly dark blue. 
In reply to a question from Prof. Hyatt as to what cause could be 
assigned for the general variation in the intensity of color mentioned, 
Mr. Allen remarked that he had long suspected that humidity had 
much to do with it, and that after determining the areas over which 
the light. and dark forms prevailed, he found by reference to charts of 
mean annual rain-fall that the lighter forms invariably occurred in 
dry regions, and the dark forms in relatively humid regions. 
Prof. Shaler remarked that he thought the difference in color at 
different localities might be an adaptation to the peculiar conditions 
of the vegetation, the paler tints of the plumage in the semi-desert 
regions better harmonizing withthe scanty gray vegetation of those 
regions than more showy colors would; the differences hence being 
such as might result from the operation of the law of natural selec- 
tion. 
‘To this Mr. Allen replied that since there was generally much 
less differe -e in color between young birds, and in old birds soon 
