JAINSON’S THRUSH (Catharus ustulatus) 
(Fig. 22 and 23) 
‘ing Migration 
Swainson’s thrushes generally begin to appear in IIli- 
sin small numbers about April 20, with not more than a 
*k to 10 days difference in arrival between south and 
th (Fig. 24). Though there are records for the north as 
ly as March 31 and early April (Ford 1956 and Abbott 
|. 1933) we suspect that these are based on misidenti- 
tions of hermit thrushes. Most Swainson’s thrushes 
s through Illinois during May, with peak populations 
sing the south in early and mid-May and the central 
| north in mid-May and late May (Fig. 24). A few 
inson’s thrushes regularly linger in central and north- 
Illinois through the first week in June. 
The migrations are probably strictly nocturnal, some- 
s lasting all night (Cochran et al. 1967, and Kjos & 
hran 1970). The migrations are often audible because 
he birds’ loud calls, which are uttered during the day 
.. We translate the calls most frequently given as 
eek” and “whit.” More rarely the calls sound like 
§. 22.—Swainson’s thrush. (The thrush with buffy ‘“‘spectacles.’’) 
“sweeur”’ or “‘peeur,”’ which are much more characteristic 
of gray-cheeked thrushes and veeries. Swainson’s thrushes 
are also strong singers during migration. 
We saw the largest numbers of Swainson’s thrushes in 
east-central Illinois, and the fewest in the south (Fig. 24). 
The pattern of high populations in the east is, in our expe- 
rience, consistent from year to year. There are no absolute 
measurements of migrant thrush populations for any locali- 
ty in Illinois, nor has anyone attempted a precise definition 
of thrush habitat. We see them in a wide variety of woody 
habitats. 
Fall Migration 
There are a few July records for the Swainson’s thrush 
in northern Illinois (Nelson 1876-1877, Ford 1956, and 
Eiseman & Shank 1962), but generally the first indication 
of the fall migration comes in mid-August or late August 
(Fig. 24). At Glen Ellyn, Gault (unpublished notes 
1884-1915) fairly regularly detected the first fall Swain- 
son’s thrushes around August 20. One specimen he collect- 
ed on August 21, 1895 was in heavy molt. The first birds to 
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