n spring. [here are surprisingly few references to these 
matic migrations in the Illinois literature (Armstrong 
0, Cooke 1883, Fawks 1967, and Musselman 121) 
‘most of them lack precise data on numbers, timing, and 
at directions. 
The arrival dates most often given are: February 1-15 
southern Illinois, February 6-25 for central Illinois, 
February 20-March 10 for the north. The earliest ar- 
ls are likely to be males, but within very few days birds 
oth sexes are present (Speirs 1946). Our censuses indi- 
d the presence of high migrant populations in southern 
10is from February 10 to April 10, and from about 
ch 10 to April 20 in central and northern Illinois (Fig. 
Xobins banded in Illinois have been recovered on the 
hern wintering grounds as late as April 5 (South Caro- 
), and March 30-31 (Georgia and Mississippi). In 
on to the regular spring migration from the South, 
5 
a on oF 
nae 
Fig. 3.—General distribution of the robin,” 
+} 
i, 
al 
there are winter (December and January) movements of 
unknown origin (see under Winter Records, below) 
Ballou (1880) believed that northward movements of 
robins began after a period of 60 hours of warm tempera- 
tures (upto 70° F.) and southerly winds. Eifrig (1922, 
1924) theorized that photoperiod was a more important 
stimulus than temperature. Our censuses showed the rob- 
in’s spring migration to be prolonged in the south, as if the 
birds tended to loiter at that latitude during February (Fig. 
4). This was also Cooke’s (1883) impression. The late Feb- 
ruary exodus of robins from southern Illinois in 1967 oc- 
curred overnight when winds shifted from northwest to 
southwest. 
In general, our spring counts of robins were lower in 
western IIlinois than for the eastern side and migrant popu- 
lations in northwestern Illinois were especially poor (Fig. 
4), 
aa 
