Fig. 25.— Brown thrasher nest (not in situ) with eggs, slightly smaller than life size. The eggs, usually 3 or 4, are whitish | 
pale green, speckled with reddish brown. 
witnessed the actual predation, but have found squirrels 
in nests that were recently active. In these instances the 
squirrel had placed green leaves in the nest and was using 
it as a diurnal resting place. In southern Illinois, the 
predator we saw at or near nests most frequently was the 
black rat snake. In north-central [linois we once saw a 
fox snake (Elaphe vulpina) eating thrasher eggs. How- 
ever, we have too little data on the identity and popula- 
tions of nest predators to understand their effect. Like 
mockingbirds and other species, thrashers will vigorously 
attack even large snakes but without much effect. An 
interesting account of such an attack is given by Nilsson 
(1957). 
Fall Migration 
By mid-August a few thrashers appear to have cor 
pleted the molt, but most are still ragged and moltin 
By early September most of them are in fresh plumage. 
There is wide discrepancy in the departure dates f 
this species recorded in the literature, ranging from mi 
August to late November. Even in July we have not 
the seeming disappearance of thrashers from a local po 
ulation. We have no idea where these birds go, or eve 
with any certainty, that they actually go, but the obst 
vations indicate a definite change in the birds’ behavior 
Most of the departure dates recorded in the literatu 
Taste 11.— Clutch sizes of brown thrashers in different regions of Illinois. 
Roe Memeo Total Number Average Percent of Nests by Clutch Size 
of Nests Clutch 5 Eggs 4 Eggs 3 Eggs 2 Eggs 
North April-May, 1968 56% 4.1 20 68 12 0 
Central April-May, 1958 ey) | 0 71 29 0 
April-May, 1959 36 aT 0 69 31 0 
April-May, 1968-1969 117 ai 1 72 7) 0 
South April-May, 1967 30 3.6 3 57 37 3 
a Includes records from literature, where complete data were provided. 
OZ 
