2s 
1.Q 
y. 39.—Annual variation in 0.9 
bluebird populations, based 
‘ubon Christmas counts in 
gions of the state. The calcu- = 
or the north (right scale) is O 7 
-y of occurrence of bluebirds — 
tage of all counts on which > 
Is were seen). The calcula- iS 
the central and southern re- < 
number of bluebirds seen per 4 
our in the field (left scale). a 
rmation about the Audubon ne 
as counts, see Cruickshank 
wn 
(a) 
a e 
co 
i 
1 \ 
! \ 
1 | 
a | 
/ 
GDN 
1940 
labits 
bes’ papers (1903) are the only systematic studies on 
1 of bluebirds in Illinois (Fig. 40). His specimens 
ken in central and northwestern Illinois, except for 
nber sample taken in extreme southern Illinois. In- 
mprised a very large part of the diet except in the 
‘ough bluebirds take much of their food from the 
they often look for prey from an elevated perch. 
ervation of Cooke (1885) that many bluebirds for- 
neadows, picking around the roots of grass, 1s in 
with the stomach analyses of Forbes, who found 
Ss-€ating cutworms were important in the blue- 
iet. In the spring, cutworms, predaceous beetles, 
i§ beetles were the principal prey. Surprisingly, 
s did not show the marked change to fruit in June 
ved for the robin and the mimids. In late summer 
crickets and grasshoppers became very important 
‘tas the intake of beetles declined. 
€ winter, the diet consisted almost entirely of fruit. 
- Was especially prominent, but grapes, sumac, 
id holly were also important. Link (1940a) also 
holly berries in the December diet, and Cooke 
so recorded sumac. In northeastern Illinois Nelson 
77) observed bluebirds eating the fruit of Virginia 
NORTH ——— 
CENTRAL —__ 
SOUTH ——— 
se 
a 
z 
(e) 
= 
kK 
& 
(2) 
2 
30 > 
z 
pe w 
(a 0 > 
Is Me 
\ / Nae « 
it AS 
lee), hy /\ 
\ \, aN Me as 
/ NV, 0 
1950 1960 1970 
BLUEBIRD - FOOD 
HYMENOPTERA (esp. ants 
& ichneumons) 
LEPIDOPTERA (esp. 
Noctuidae) 
COLEOPTERA (esp. ground 
beetles & scarabs) 
HEMIPTERA (stink bugs) 
< 
ORTHOPTERA ie 
(grasshoppers) ra 
[@) 
ARACHNIDA z 
w 
UO 
MYRIAPODA w 
rn ae =. ce 
FRUIT (mistletoe, grapes, 
sumac, haws & holly) 
ES SeRUAN Pes 
Tres MAR APR MAY JUN JUL AUG SEP 
Fig. 40.—Food habits d 
dy of Forbes, 1903 (1880). 
identified in the stomachs o0 
ata on the eastern bluebird based on the stu- 
Percentages represent the part of the total food 
f a number of bluebirds examined each month. 
4] 
