NESTS or YOUNG 
@ 1950- 
A 1900 - 1949 
@ BEFORE 1900 
PAIRS or SINGING 
MALES (JUNE) 
CO BEFORE 1900 
A 1900-1949 
TAZEWELL Me LAN 
O 1950— 
BLUEBIRD 
BREEDING RECORDS 
Scale 
10 0 10 20 30 _40_SOMiles 
Fig. 36.—Breeding records for the eastern bluebird in Illinois. Sing- 
ing male records are for June only. 
areas in west-central Illinois, occupancy of houses by | 
birds fell about 23 percent between the first (April 
May) and second (June and July) nestings, with the 
tremes in different years being as low as 8 percent ar 
high as 66 percent (based on data from Musselman | 
1936, and Evers 1937). Bartel (DuMont 1947) recorde 
exceptionally high rate (90 percent) of “‘second-nest 
occupancy in 1947 at Blue Island. There are no com} 
tive data for the south. 
The bluebird appears to have a prolonged nesting 
The full cycle for one nest observed in central Illinois, 
nest-building to fledging of young, required 47 days ($ 
1939), but this was an early nest, started April 5, anc 
building was slow (12 days). Nests have been buil 
days or less (Musselman 1934-1935, and Varner | 
We have recorded nest-building periods of 6 and 7 di 
southern and central Illinois, with incubation peric 
13-15 days (most frequently 14 days), and nestling pe 
of 15-17 days (most often 16 days). Holcombe’s ( 
observations in the north also indicated an incubation 
od of 14 days, and nestling period of 16 days. Thus, 
cycle, including egg laying for a nest with five eggs m 
expected to take about 40 days. 
Throughout the state, most nests receive 5 eggs f 
first nesting, but clutch size declines in later nests, esf 
ly in the south (Table 7). Among the hundreds of ne 
observed Musselman (1946a) once recorded a clutch | 
en eggs, and once nine eggs in one nest, contributed t 
females. 
The eggs are generally pale blue, but sometimes 
and rarely are both types found in the same nest. In] 
tensive studies in west-central Illinois Musselman | 
1946) found about 5-6 percent of the eggs to be white 
Tape 6.—Breeding populations of bluebirds in various I}linois habitats. 
Birds Per Type of Region or 
Habitat Acres 100Acres* Years Census County Reference 
Orchard 5 80 1936 Nest Lake (N) Beecher 1942 
Edge shrubbery 9 34 heey Strip South Graber & Graber 1‘ 
Block shrub areas 67 | 1957 Strip South Graber & Graber I' 
Late shrub ie 10 1966 Nest Vermilion (C) Karr 1968 
Thicket ie) 1 1950 Nest Jackson (S) Brewer & Hardy 19 
Residential 8 PES 1916 Nest Richland (S) Cooke 1916 
Parkland estate 100 £2 1915 Nest Cook (N) Eifrig 1915 
Unmodified woods 2 15 1936 Nest Lake (N) Beecher 1942 
Forest (all types including edge) 19 l 1957 Strip North Graber & Graber !' 
174 Z South 
Forest edge 55  (0-2permile) 1927-1970 Nest Champaign (C) Kendeigh 1948, 
Kendeigh & Clemai 
Second growth or cut-over woods LS 13 1937-1938 Nest Rock Island (N) Fawks 1937, 1938 
Grazed bottomland 93 4 1955 Nest Macon (C) Chaniot & Kirby 1° 
Pastureland 147 3 1957 Strip North Graber & Graber ! 
54 2 Central 
ee, 8 South 
4 All figures were converted to read birds per 100 acres or birds per mile of edge ( 
38 
number of territorial males or nests x 2). 
