E         tleopolb 
 Repriut1'd  from  1]iiioi,  .vwdeide   of  Sei(,ioe  T'r.  'to,  Vol. 34,
No. 2,  De(.,  1941. 
 
 
 
 
DISTRIBUTION OF UPLAND BIRDS IN ILLINOIS 
                       S. CHARLES KENDEIGt1 
               University of Illinois, Urbana, Illinois 
 
 
  According to the life-zone concept of 
Merriam and others, distribution of birds 
falls into natural units consisting of 
great trans-continental belts. Seven of 
these zones have been     described for 
North America, each bounded on the 
north and south by isotherms of tem- 
perature. With the recognition that dif- 
ferent species occurred in the west as 
compared with the east, certain zones 
were subdivided at about the 1000 merid- 
ian on the basis of differences in humid- 
ity and rainfall. If one follows this con- 
cept the state of Illinois falls mostly in 
the eastern Carolinian Faunal Area of 
the Upper Austral Zone. The Transition 
Zone enters the state on the north and 
the Lower Austral Zone on the south, 
but the extent of penetration appears to 
be a matter of personal judgment. Such 
a concept is unsatisfactory for analyzing 
the distribution of the three hundred or 
so species of birds that occur, as it pre- 
supposes a uniform occurrence of a dif- 
ferent group of species in each section of 
the state with their distributional bound- 
aries determined only by temperature. 
  Doubtlessly temperature does affect the 
distribution of birds. For instance the 
chuck-wills-widow, Carolina   chickadee, 
Bewick   wren, mockingbird, sycamore 
warbler, Kentucky warbler, hooded war- 
bler, summer tanager, Bachman's spar- 
row and others are found more commonly 
during the breeding season in the south- 
ern portions of the state, and the black- 
capped chickadee, swamp sparrow, bobo- 
link, clay-colored sparrow, and savannah 
sparrow are mostly confined to the north- 
ern portion. Very likely all species have 
limits of tolerance to extreme tempera- 
tures, but these limits vary widely be- 
tween species. When temperature con- 
trols distribution there is little agree- 
ment between different species in exact 
limits of distribution. Likewise correla- 
tion between distributional boundaries 
and isotherms does not prove that tem- 
perature is the controlling factor without 
supporting experimental evidence. For 
instance, the northward dispersal of the 
 
 
Bewick wren appears limited by competi- 
tion with the house wren, rather than by 
the direct influence of any physical en- 
vironmental factor. 
  In seeking units of significance for the 
analysis of distributional phenomena, it 
is best to utilize the organisms them- 
selves rather than any combination of 
environmental factors. Unless distribu- 
tion limits show some harmony and cor- 
relation, then  distributional units, as 
such, do not exist in nature. Actually, 
plants and animals do exhibit fundamen- 
tal distributional interrelations in the 
form of biotic communities. These com- 
munities give the most substantial basis 
for interpreting distribution. Exclusive 
of aquatic areas, two major communities 
or biomes are represented in Illinois: 
the forest and the prairie. Their occur- 
rence in the state is shown in fig. 1 which 
was prepared originally by the Illinois 
State Natural History     Survey'.  The 
limits of the constituent avian species are 
controlled by a complex of environmental 
conditions, in which moisture, light, and 
vegetation are especially important. 
    In addition to these climax communi- 
ties, there are numerous disturbed areas 
and subclimax or developmental com- 
munities. Most of the prairie has been 
destroyed for purposes of agriculture or 
has been greatly modified. Forests have 
been lumbered or grazing has been per- 
mitted so that they no longer repre- 
sent original conditions. Marshes, lakes, 
and rivers are subclimax, but if left alone, 
the smaller lakes and ponds will gradu- 
ally become choked with vegetation and 
transformed into communities similar to 
those now on the upland. Meanwhile 
they have a varied and characteristic 
bird fauna of ducks, grebes, coots, rails, 
gallinules, bitterns, herons, and several 
species of song birds. 
  From studies carried out in Trelease 
Woods at the University of Illinois, a 
typical list of species occurring in an up- 
land forest in approximate order of their 
abundance is as follows: indigo bunting, 
starling, red-eyed vireo, crested flycatch- 
 
 
'Telford, C. J., Bull. Ill. Sta. Nat. 11ist. Surv., 16, 1926: I-VI, 1-102.