392 THE IRREGULAR MIGRATIONS OF BIRDS. 
Yet at the west, it has now exactly the habits described by 
Wilson, frequenting the orchards and coming into the busiest streets 
of considerable towns with the freedom and unconcern of the 
warbling vireo and chipping sparrow ; indeed, so familiar are they 
that they frequently alight on the roofs of houses, and tap on the 
shingles, looking down occasionally, with the utmost sang froid, 
upon the passers-by. Here, if I mistake not, is a gradual with- 
drawal from certain regions of country, and a change in the habits 
of those few remaining. 
A similar disappearance has taken place, from some localities at 
least, of the hairy woodpecker. Of this bird I never shot more 
than a single specimen at Orange, though hunting for it for 
many years, through quite an extensive range suitable for its hab- 
itat. Yet according to Wilson, it was everywhere one of the most 
abundant and familiar birds in the Atlantic States ; an observation 
indéed, made by other authors, and which I have confirmed myselt 
at several points, yet for some unaccountablé reason it has failed 
to take possession of a considerable region, admirably adapted 
apparently to his habits; or, if it ever did occupy it, for some 
equally unaccountable cause, has almost wholly deserted it. 
The Carolina parrakeet is another instance of a gradual with- 
drawal from a former range, the bird rarely appearing now, where 
formerly it was quite abundant. This may be partially accounted for 
indeed, by the settlement of the country; the valley of the Ohio, 
where it was formerly common, having, in the course of half a cen- 
tury, been converted from a wilderness into a thickly settled coun- 
try. But this explanation is only partially satisfactory ; for in its 
former range are still large tracts of almost primitive wilderness, 
where it might find every requisite for its existence. - 
Tn certain portions of Colorado the raven is now a rare bird 
where, as the miners have informed me, it was very common, fifteen, 
or even ten years ago. 
Some of these migrations may be easily explained. Many of 
them occur through human agency ; others through climatic modi- 
: _ fications. As the settlement of the western frontiers extends, the 
quail and the prairie hen, finding abundance of food, extend their 
range correspondingly ; and as trees are planted on the plains,* 
et 
: *A curious question arises here. The vast tract of treeless prairie lying between the 
Missouri river and the Rocky Mountains, forms at present, a very complete barrier be- 
n th yl p i fthet gi » Whi > ot a ib į the sottle-~ 
