4 GEOGRAPHICAL KACBS. 



of climate upon the color and size of birds;* (6) the relation ol a 

 bird's color to its haunts and habits.f Besides these general subjects 

 which enter into our study of the life-history of every bird, we have 

 the special instances of intelligent adaptation to changed conditions 

 of lite, and, most interesting of all, the relation between structure and 

 habits, or the part played by a bird's habits in determining the form 

 of its bill, feet, wings, and tail. Thus the Crook-billed Plover of New 

 Zealand turns over or probes under stones and shells in search of food, 

 not because its crooked bill makes an excellent lever or probe, but it 

 hiis acquired a crooked bill through this habit. Again, the Gallinules of 

 certain islands in southern seas are flightless, not because their wings 

 are too small to support them, but because after having flown to these 

 islands they had no further use for wings, which in time, through dis- 

 use, became so small that the birds have lost the power of flight. In 

 other words, it is not because their wings are small that they do not 

 fl.y, but because they do not fly their wings are small. 



But to enlarge upon these problems which confront the philo- 

 sophic ornithologist would require a volume. It is important, how- 

 ever, that the student should have in the beginning at least a general 

 idea of the effect of climate on the size and color of birds and the 

 migration of birds. The first is well illustrated by our Bob-white or 

 Quail. In New England, at the northern limit of its range, it is a fine, 

 large bird with a light-brown back and a white breast narrowly barred 

 with black. As we proceed southward it becomes smaller, the brown 

 is of a deeper shade, the black bars of greater extent. Finally, when 

 we have reached the humid region of southern Florida, the minimum 

 in size is attained, the back is dark, rich chestnut barred with black, 

 and the breast is almost wholly black. No one who compared this 

 small, dark Florida Quail with the large, pale Quail of New England 

 would consider them the same species. But on examining a series of 

 Quails from all the Atlantic States one sees how gradually this change 

 in color and decrease in size occurs, and that nowhere would it be 

 possible to draw a line separating the two extremes. They are species 

 in process of formation still connected by a chain of natural links. 



Ornithology presents many similar cases. They illustrate two laws 

 in the evolution of animals — decrease in size southward and greater 



* Bead Part III of Dr. .1. A. Allen's Mammals and Winter Birds of East 

 Florida, Bull. Mus. Comp. Zool., vol. ii, No. 3. Cambridge, 1871. 



t Consult Poulton's Colors of Animals (D. Appleton & Co., 1890) ; Bed- 

 dard's Animal Coloration (Macmlllan & Co.) ; Keeler's Evolution of the Colors 

 of North American Land-birds (Occasional Papers of California Academy of 

 Sciences, iii, 1893) ; also reviews of last two works in The Auk, x, 1893, pp. 189- 

 199, 373-380. 



