° 200 400 600 
miles 
Nesting Cycle 
The Illinois literature is essentially devoid of quantita- 
tive data on the nesting cycle of the wood thrush and we can 
add little. Singing has been recorded from April 19 in 
southern Illinois to August 3 in the north. Our records on 
the span of dates for egg laying, from April 26 in the south 
to July 19 in the northern and central regions, are very in- 
complete, particularly for the south. A record of young 
leaving the nest May 30 in the Chicago region (Ford 1956) 
must be exceptional as an early nesting record for that lati- 
tude. 
There is a very high incidence of cowbird parasitism. 
From our records and the literature, we have egg data on 
only 69 wood thrush nests in Illinois, of which 33 (48 per- 
cent) were parasitized. Most of the nests had 1 or 2 cowbird 
16 
800 
eo 
tm 
x 
& 
x 
s 
nc roe AA 
tn 
x Ri , 
= e 
A 
Fig. 13.—General distribution of the wood é 
thrush. 
oh 
ae y y 5 
Ranges~——-- | ee 
4 = == * Bt 
BREEDING ~* a a a 
ES winter : 
+ S&S 
- ms s e ae: é 
ae 
eggs, but 6 nests had 3 or more (up to 5). Though the 
ple is small it represented all three regions of the stat 
the incidence of parasitism was near 50 percent in ea 
gion. This high parasitism has been reported over 
years. Mundt (1883) found nearly half of the nests 
the Vermilion river bottoms parasitized. Twomey | 
recorded fledging success of 78 percent for 23 thrush € 
nests), and 33 percent for 3 cowbird eggs (3 nests). : 
In the sample of 36 nonparasitized nests, clutcl 
were as follows: 5-egg, 9 percent; 4-egg, 76 percent, | 
15 percent. | 
There are no data on longevity or on mortality f 
Montgomery (1956) felt that wood thrushes survived 
than robins following DDT applications for elm d 
because the wood thrushes arrived later after the ins 
treatment. 
