GEOGRAPHICAL DISTRIBUTION. 29 



such general occurrence that even the exceptions, if such there really be, 

 are exceedingly few : 



" 1st. As regards size: There is a general reduction in the size of the 

 individual, from the north southward, amounting not unfrequentl}?- to as high 

 as 10 to 15 per cent, of the maximum size of the species. The reduction 

 is much greater in some species, and in some groups of species, than in 

 others, but is almost invariably considerable and easily recognizable. 



"2d. 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 size, but 

 especially in thickness. Those of a slender alternate form become slenderer 

 and relatively longer at the southward, with a decidedly greater tendency 

 to curvature. 



" 3d. In respect to the claws : A similar increase in size is apparent in the 

 claws, especially in that of the hallux, at southern localities, perhaps less 

 marked and less general than the increase of the bill, with which it evidently 

 correlates. 



" 4th. In respect to the tail : A marked elongation of the tail at the south- 

 ward has been noticed in many cases, both in Cape St. Lucas birds (Baird) 

 and in those of Florida. 



" 5th. In respect to color : The differences in color are especially obvious, 

 and may be reduced to two phases of modification : (a) a general increase 

 in intensity at the southward; and (b) an increase in the extent of dusky or 

 black markings at the expense of the intervening lighter or white ones, or, 

 conversely, the reduction in size of white spots and liars. Under the gen- 

 eral increase in intensity, the iridescence of lustrous species becomes greater, 

 and fuscous, plumbous, rufous, yellow, and olivaceous tints are heightened 

 in species with the color continuous in masses. 



Under the repression of light colors, the white or yellowish edgings and 

 spots on the wings and tail become more or less reduced ; and frequently, to 

 a great degree in species barred transversely with light and dark colors, the 

 dark bars widen at the southward at the expense of the white or lighter 



