forests, 
cies, as 
species, 
sults in 
course, 
THE IRREGULAR MIGRATIONS OF BIRDS. 393 
the insectivorous and arboreal species will become abundant in re- 
gions where they previously could not exist. The destruction of- 
and the draining of swamps must, of course, result in the 
diminution of the numbers of the forest and swamp loving spe- 
seen very plainly in England at the present day; and 
again, the protection afforded from predaceous animals, by the 
presence of man, and the thinning out of birds of prey, must 
necessarily result in a great increase of the smaller and inoffen- 
sive tribes. On the other hand, the persecution to which certain 
mainly rapacious, or valuable for food, are subjected, re- 
their thinning out or even extermination, unless, as often - 
happens, they migrate to other and wilder regions. 
Climate influences many extraordinary migrations. A severe 
winter will cause northern birds to migrate much further south 
than usual, anda long hot summer will entice southern birds to visit 
us, which we do not see in ordinary seasons. Such migrations, 
however, are only temporary, although I am inclined to think that 
birds may subsequently revisit regions, purely from choice, to 
which in the first place, they were compelled to fly for safety. 
And again, extraordinary seasons may have an indirect influence 
upon these movements of birds. In a recent interesting little 
article in the Narurauist, Prof. Shaler shows how the flora of New 
_ England was probably modified by the recent cold winter ; and of 
a modification of the flora would result in a correya 
modification of the avi-fauna. Thus, the coniferous trees being 
uced in numbers, there would be a similar reduction in the 
abundance of pine grosbeaks, finches, crossbills, and other spe- 
cies, more or less dependent upon the Coniferæ for food. The 
insect fauna also, closely connected with, and necessarily affected 
by the slightest change in the flora, must undergo some readjust- 
ment, resulting in- a corresponding change among the tan 
rous birds. : 
ae io. ioe ee 
ment of the plains proceeds and trees are planted, this barrier will gradually cease to 
pata the arboreal faune of the et mountains and the eas 
meet each other. What niin be the result on suc. such allied c 
as Op Carolinéneins 
Me pam 
Willeac 
- the one into the other? Sturnella Ludoviciana and S. neglecta, 
h pres erve its pec E or will, a hybrid race arise, € 
side b; 
tain peculiar notes ma habits. On terng hand, 
