(Parus carolinensis) occupying from about 10 to about 40 
percent of the bluebird boxes, with bluebirds occupying 60 
percent of the boxes. We witnessed no aggressive competi- 
tion. However, in northwestern Illinois Wilson (Hodges 
1954) observed that bluebirds and black-capped chickadees 
were keen competitors. In the same region Schafer (1920) 
saw redheaded woodpeckers destroy bluebird nests, and we 
have seen one such incident in the south. 
Eifrig (1937) suspected that starlings (Sturnus vulgaris) 
were important competitors of the bluebird (see also Schaf- 
er 1932, and Musselman 1934a, 1942), but this competi- 
tion can be eliminated on nesting box routes by proper box 
design and placement (Varner 1964). Varner also warned 
that boxes near water tend to be taken over by prothono- 
tary warblers (Protonotaria citrea), and tree swal- 
lows (Iridoprocne bicolor). 
Bluebirds also have to compete for cavities with small 
mammals, notably deer mice (Peromyscus) and flying 
squirrels (Glaucomys volans), and with wasps 
(Musselman 1934, 1947). 
There is little information on other causes of nest loss. 
Musselman (1946) considered loss from snake predation to 
be small, but cautioned (1935, 1940) that boxes in brushy 
or weedy places are particularly susceptible to black snake, 
shrike, and mouse predation. 
Persons who wish to establish bluebird nest-box routes 
should read Musselman (1941, 1944), Varner (1964), and 
Kibler (1969) for valuable instructions. 
Fall Migration 
Our data indicate that most of the fall migration occurs 
from September into early November in central and south- 
ern Illinois (Fig. 35). Our earliest observation of actual 
migration flights in southern Illinois was September 17 and 
the latest was November 6, but both these dates probably 
fall short of the true extremes. 
In our experience, bluebird migration was never the 
massive steady flow of birds as in the case of robins, blue 
jays, and other diurnal migrants. Bluebirds flew inthe 
morning in small, loose flocks going south and southeast. 
Nelson (1876-1877) dated the fall migration in north- 
eastern Illinois from September 12 to October 25, and this 
closely coincides with the timing of our high census figures 
for the north (Fig.-35). Schafer (1922) recorded exception- 
ally large migrations in the north in 1922 nearly every day 
in September and early October. 
The numbers of bluebirds seen in the fall (September 
into November) consistently exceeded the spring (Febru- 
ary through May 10) counts throughout the state. The ra- 
tios were one bird in the spring to three in the fall for cen- 
tral Illinois, one to six in the south, and one to eight in the 
north. 
There are very few published band recoveries to indi- 
cate destinations of migrating Illinois bluebirds. Birds 
banded in the spring and summer in northeastern and west- 
central Illinois have been recovered in the winter from 
southeastern Texas to southern Louisiana and southern 
Georgia (Bent 1949, and Musselman LOST): 
40 
Winter Records 
Bluebirds have been found in all regions of the sta 
the winter (Fig. 38), but 90 percent or more of the st 
winter population is in the southern zone (Graber & | 
ber 1963, and Fig. 39). In about one-third of the y 
there are no bluebirds recorded in the northern and ce 
Christmas counts (Fig. 39). They are most likely | 
found along major rivers, especially in the northern h: 
the state (Fig. 38). The species is usually found in s 
flocks of 3-20 birds. 
The bluebird’s population crashes, as discussed \ 
Nesting Habitats and Populations above, show up cl 
in the Christmas counts (Fig. 39), and there is good ¢ 
lation in time between the low breeding populations 
low populations in winter (Fig. 37 and 39). 
Our censuses showed pastures and other grassl 
forest edge, and shrub areas to be favored winter ha 
(Graber & Graber 1963). The only absolute measure! 
of winter populations are by Shaw & Scherer (1960) 
Shaw et al. (1964), who censused a shrubby field ar 
southern Illinois and found densities ranging from less 
one bluebird per 100 acres to seven per 100 acres il 
year census period. 
WINTER RECORDS 
DEC.1- JAN. 31 
ears ce 
e 1950 1h Jo oe iam aer 8 | McHENAY 
Tt sa pes 
A 1900- 1949 (a 
CARROLL | tt 
2 al; Bs wns| bo 
W BEFORE 1900 bea [ Lo ete 1 
€ ae “<7 
i wy ene Bee 
: 
c@er PUTNAM! 
MARSHALL, 
Waren LIVINGSTON | 
vid 5 
peer ie ‘a EAN ‘ 2 | 
“a 
mine. ee 
Dams 
S 
BRO case) Ue 
@ im ee - a a. Ss 
aa worcan | SANGAMS —T (pouste 
PIKE scorrh 5 OULTRIE —_—- 
+ CHRISTIAN OLE 
TOT | eo 
ea! GREENE SS ae Ley ., 
macoupin | MONTGOMERY 
re | wes eee a 
LY 
MADISON 4 a 7 oar” mn 
CLAY Vance 
$ 
Pa 
g iP E Op WOODFORD 
# 
BLUEBIRD « 
CLINTON = 
= 
ST. CLAIR WAYNE 
INGTON 
wy © WASHINGTON | son 
3 41 i 
RAWDOLPH Pel 2 Gada d 
me) 
aac ny | SALINE OALLA 
5 + eS 
ARO 
= ais 
te AROMP 
< onnson » 
ts _— en 
10.010 20/39) °40_SOMiles ge Ws, 
ea a a a v 
CR 
Fig. 38.—Winter records for the eastern bluebird in Iilir 
three regions of the state discussed in the text are shown by heavy 
