118 GAMBLES ABOUT 



one thousand, as near as I can judge ; and, in proportion 

 as the winter is mild, the percentage of those that remain 

 is increased. In Massachusetts, this bird is strictly mi- 

 gratory, the great bulk of those that depart from the 

 north and from New Jersey wintering in the Carolinas 

 and Georgia. In this species, therefore, we have an 

 example of a migratory bird that is gradually becoming 

 more and more accustomed, not to the rigors of winter, 

 which birds are better able to withstand than they are 

 generally supposed to be, but to the methods of our winter 

 residents, such as wood-peckers, jays, and titmice, in pro- 

 curing seasonable food. As a matter of course, food, and 

 an abundance of it, must necessarily be obtained, and, on 

 examination of the stomachs of grakles killed in January, 

 I have found them filled with a half-digested mass of 

 what appeared to be both animal and vegetable matter. 

 If the grakles that remain during the winter are of a 

 hardier constitution than those that migrate, then, as they 

 mate very early in the year, and before the great bulk of 

 the southern sojourners reach us, their offspring will nat- 

 urally inherit equally vigorous constitutions, and, like their 

 parents, will be more disposed to remain at least, a large 

 proportion of them will be and in this way, wholly 

 through natural selection, a race of grakles, otherwise un- 

 distinguishable from the whole number of this species, 

 will be evolved, that in time will replace, in great part, 

 the now migratory and semi-migratory individuals. If I 

 have correctly explained a change now in progress, in 

 the habits of this and other species, then can we not from 

 it gain a clew to one, at least, of the original causes of the 

 habit of migrating? 



The act of migrating being the passage from one dis- 

 tant point to another, it is evident that the cause or 

 causes of this movement, as the case may be, operate at 



