18 BIRDS OF OHIO. 
bly north of their normal summer range in Ohio, seems to 
indicate that this Lower Austral extension may be approach- 
ing our southern border, as far as the birds are concerned. 
This impression is emphasized by the numerous unconfirmed 
reports of the occurrence of the Nonpareil and Blue Gros- 
beak in the vicinity of Cincinnati. A further indication of 
the tendency of the birds, in the latitude of Ohio, to move 
gradually northward with their breeding range, is shown in 
the increasing number of species which remain during the 
entire winter. It indicates that hardier individuals are grad- 
ually being developed. Since Ohio lies near the northern bor- 
der of the breeding range of several species, and just above 
the northern range of some others, we may expect that the 
hardiest individuals of such species will gradually invade 
regions to the north of their range which have not known 
them hitherto. This law of differentiation is recognized 
in a practical manner by those who see sub-specific differ- 
ences between the individuals of certain species which habit- 
ually remain well south to breed and those which habitu- 
ally push well north to breed. This seems to be one of the 
methods for the development of species. 
The appearance of northern breeding birds in the state 
in winter cannot properly be classed as invasions, because 
they are forced south by the stress of hunger, and return 
at the first opportunity. It seems clear that during the mi- 
grations of the species which breed north of the state, the 
movement of species in the western end of the state is a 
little west of north, and in the eastern part of the state a lit- 
tle east of north. While Lake Erie is not an insurmountable 
barrier to most species, they seem to prefer not to cross it di- 
rectly or at all if possible. I have repeatedly seen Killdeers 
and Meadowlarks strike out boldly for the Canada side, 
with a favorable wind, only to turn back before they had 
passed out of sight. It is more than likely that many indi- 
viduals of the species which migrate by day pass around 
the ends of the lake, or cross at Sandusky. 
