BROWN THRASHER (Toxostoma rufum) 
(Fig. 18 and 19) 
Spring Migration 
The onset of the thrasher’s spring migration is some- 
what obscured because of the thin winter population, and 
the paucity of birds involved in the earliest flights (Fig. 
20). This early influx, which reaches southern and cen- 
tral Illinois in late February or early March and northern 
Illinois in late March, may be a different phenomenon 
than the larger migrations that start 2 weeks to a month 
later. At least the later migrations are probably nocturnal. 
—NUMEBER OF BIRDS 
mmo 2030 9 «219 «29 «9 19 09 One specimen was recovered with other night migrants 
on the night of May 6-7 by Brewer & Ellis (1958). 
AUG SEP OGh The most frequently mentioned arrival dates for 
southern Illinois are March 21-27 (Ridgway 1889, Cooke 
1888). Our census data indicated major movements of 
thrashers from March 26 through most of April and May 
with peak numbers in late April and early May (Fig. 20). 
Thrasher arrivals in central Tlinois have been noted 
especially from March 23 to April 1, and there were 
marked waves from April 1 to 13 (Hess 1910, Smith 1930, 
and others). The 1969 census data indicated relatively 
large migrations throughout April and May with peak 
numbers in late April. The highest counts were obtained 
in the western study area along the Illinois River valley. 
March records of thrashers in northern Illinois are 
unusual, and the most frequent arrival dates mentioned 
are April 10-17 (Abbott, et al. 1933, Kerber 1923, Gault 
1901, and others), with the peak numbers following 
quickly in late April (Fig. 20). 
There was relatively little difference in the timing 
of the peaks of the thrasher migration in southern, cen- 
tral, and northern Illinois. A noteworthy difference, 
however, is that in southern Illinois thrashers of the local 
breeding population established nests before the peak in 
migration, while in central and northern Illinois most 
nests were established after the peak (Fig. 20). This 
lends credence to the idea that the peak counts actually 
— 10): a ae: a: represent the passing of transients, i.e., birds enroute to 
AUG SEP OCT places farther north. We have only one banding recovery 
to indicate where transient thrashers are headed in the 
spring. A bird banded at Urbana, April 22, 1965, was 
recovered the following April due north in eastern Wis- 
consin (Fig. 26). 
— NUMBER OF BIRDS 
Distribution 
NUMBER OF BIRDS The general distribution of the brown thrasher is 
shown in Fig. 18. The thrasher probably nests in every 
Fig. 20.— Nesting and migration seasons of the brown 
thrasher in different regions of the state (see Fig. 1). Spring 
and fall graph lines show the highest daily counts of each 2 
days (left hand scale). The lines are interrupted where data 
have not been collected. Shaded block indicates length of the 
nesting season and level of adult nesting population. Circle 
points represent censuses in the [Illinois valley; solid points 
represent east-central Illinois. Egg-laying graph line (right hand 
scale) is based on repeated searches of roadside habitat through- 
out the nesting season. 
AUG SEP OCT 27 
NESTING 
