° 200 400 600 800 
miles 
bird population in west-central Illinois succumbed to cold 
and snow one spring. In ‘Tennessee, which is part of the 
bluebird’s winter range, Laskey (1958) found many dead 
bluebirds that had been roosting in nest boxes (as many as 
12 dead in one box) after severe cold and snow in mid-Feb- 
ruary. We have also found dead bluebirds in roosting cavi- 
ties in February in southern Illinois, and Musselman 
(Peterson 1965) found dead birds in his nest boxes in April. 
Nesting Cycle 
Banding returns reported by Bartel (1950, 1952), Hol- 
combe (1930, 1932), and Musselman (1934) show that 
some young bluebirds as well as adults return to the areas 
of their birth and the adults sometimes return to the same 
box. However, no quantitative data have been published to 
show what part of the population returns. Musselman 
(1934) felt that young birds tended to scatter more. 
36 
Fig. 34.—General distribution of the 
bluebird. 
There is little reference to the bluebird’s song int 
nois literature, and nearly every mention of the son; 
to the month of March as the time of singing. Ri 
(1889) indicated that there was a resurgence of s 
song in August, but the periodicity of singing has n 
recorded in any systematic way. 
The earliest nest with eggs for Illinois was 1 
March 20 by Musselman (1937) in central Illinois 
is no indication that nesting begins earlier in the sou 
35). The laying curves for the bluebird have severa 
The first peak occurs in April throughout the stat 
about a 12-day lag in the north (Fig. 35). There : 
laying peaks in May and June, and though a few 0 
established as late as mid-August, laying 1s largely 
the end of June. 
Musselman’s work with banded birds show 
bluebirds tend to have two broods in one season. 
pair of bluebirds may use the same box for two con 
