THE MIGRATION OF INLAND BIRDS. 191 



birds, the more prolonged autumn stay of the latter, we think, ex- 

 plains itself. In the spring, there is an object ever in view, while on 

 their journey north in autumn, their sole care is to be home in time; 

 not so much to escape the coming cold, as to avoid being pinched by 

 hunger. * 



We have seen that the first frost that but little affects vegetation 

 does materially decrease insect-life ; the swallows even anticipate this 

 first frost, and, gathering in immense flocks, wing their way south- 

 ward long before it comes. We can clearly see that the weather 

 greatly influences, indeed governs, the migratory movements, in au- 

 tumn, of the insect-eaters. It bids them dej^art, and, in general, they 

 heed the bidding ; but long after this, while there are yet berries, 

 seeds, and fruits, to be obtained, the migratory vegetarians linger, in 

 varying numbers, by the way. 



Let us now glance at the abundant and well-known purple grakle 

 or crow-blackbird [Quiscalus 2)urpureus). The nunibers of this (with 

 us) partially migratory species that remain throughout the winter, as 

 compared with those which are here during the spring and summer 

 months, are about as three to one hundred, as near as we can judge; 

 and, in proportion as the winter is mild, the percentage of those that re- 

 main is increased. In Massachusetts, this bird is strictly migratory ; 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 Avithstand than they are supposed to be, but to the 

 methods of our winter residents, such as woodpeckers, jays, and tit- 

 mice, in procuring such food as can then be procured. Food, as a 

 matter of course, and an abundance of it, must necessarily be ob- 

 tained, and, on examination of the stomachs of grakles killed in Jan- 

 uary, we 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 naturally 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 natui-al selection, a 

 race of grakles, otherwise undistinguishable from the whole number of 

 this species, will be evolved, that in time will wholly replace (?) the 

 now migratory and semi-migratory individuals. If we have now cor- 

 rectly 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 ? 



But this we will discuss in the concluding part of our essay. 



The act of migrating being the passage from one distant point to 



