prairie chicken range is #acquired" tertitory, into which they have been
pushed by the plow, after axe, fire and olow had made it habitable for than.
The qualitative center of the ruffed grouse range, in our opinion,
was the hardwood timber region extending acro 1s the continent to the prairies
in the latitude of southern Michigan. Here also the ruffed grouse has been
reduced in habitat and numbers to such as extent that a saturation point would
be invisible, even if it had once existed. In both the prairie chicken and
raffed grouse, Aowever, Leopold, Allen, Gross and other investigators, have
found a tendency for the severity of the cycle to decrease as one approaches
this assumed optium region. There are "islands" of both raffed grouse and
prairie chickens today inOhio, Indiana, Illinois and Iowa where local observers
who do not read natural history periodicals do not know the meaning of cycles
or other fluctuations in these species. On these islands they anpear to be
"straight line" species.
The evidence, as far as it goes, seems to support the assumption that
saturation points in gallenaceous birds are the prevailin- check on over-
povulation near the center of distribution of the species, and that cycles or
irruptions are the prevailing check on the ede-e of the range of each species.
When we have said this we have said that both cycles and the saturation point
are a property of the environment, and that each gallinaceous-species exhibits
either the one or the other, depending on whether the environment is central
or peripheral, PIA^-LA               * 0(AeAc
This cannot be adopted, however, even as a working hypothesis without
reconciling it with the known fact that all of the grouse exhibit violent
cycles throughout Canada and Alaska. Can this enornous area by rega.rded
as on the sedge" of their range? In the sense of geographic miles, obviously
not. In the case of species such as ptarmigan, it is not the edge in any