536 GEOGRAPHICAL VARIATION IN NORTH AMERICAN BIRDS. 
1. As regards Size. There is a general reduction in the size of 
the individual from the north southward, amounting not unfre- 
quently to as high as ten to fifteen per cent. of the maximum siz 
of the species. The reduction is much greater in some species, 
and in some groups of species, than in others, but is almost inva 
riably considerable and easily recognizable. 
2. In respect to the Bill. The variation of the bill is somewhat 
inverse to that of the general size, as a rule the southern forms 
having generally relatively, and often absolutely, larger bills | 
than northern ones, the increased size taking different proportions 
in different species and different styles of bill. Those of a stout, 
thick, conical form generally increase in general size, but espe 
cially in thickness. Those of a slender, attenuate form ey 
slenderer and relatively longer at the southward, with a decidedly 
greater tendency to curvature. 
3. In respect to the Claws. A similar increase in size is app 
ent in thé claws, especially in that of the hallux, at southem — 
localities, perhaps less marked and less general than the increase : 
of the bill, with which it evidently correlates. 
4. In respect to the Tail. A marked elongation of the tail . E 
the southward has been noticed in many cases, both in Cape St : 
Lucas birds (Baird) and in those of Florida. en 
5. In respect to Color. The differences in color are especially n 
obvious, and may be reduced to two phases of modih : 
(a) a general increase in intensity at the southward, and (b) oe 
increase in the extent of dusky or black markings at the i e b 
of the intervening lighter or white ones; or, conversely, oul 2 
duction in size of white spots and bars. Under the & eee _ 
increase in intensity the iridescence of lustrous species = a000 
nd olivac®™" 
greater, and fuscous, plumbeous, rufous, yellow ane ' 
tints are heightened in species with the color continuous 10 
at the expense of the white or lighter ones, sometimes 10 ©. 
extent as greatly to change the general aspect of ae ae 
is the case in the Ortyx virginianus of the Atlantic States, ie 
other well known species. Also under the tendency on 3 light 
crease of dark colors, longitudinal streaks and blotches °F — 
ground increase in extent and intensity of color. 
