Food Habits 
The food habits of the eastern wood pewee in Illinois 
are inadequately known. Three stomachs from pewee 
specimens collected in Tazewell County and examined by 
Forbes (1882a) contained chiefly unspecified flies and 
gnats (55 percent of the food) and small beetles (23 
percent) plus ants and other Hymenoptera. Rice's (1946) 
study also shows Diptera to constitute the principal food 
(35-50 percent of the food), with Hymenoptera (20-25 
percent), Coleoptera (10-20 percent), and Lepidoptera 
(5-15 percent) also important in the diet. 
Lyon (1925) once saw a wood pewee steal a butterfly 
from a woodpecker, but if such pirating behavior is 
common it has generally escaped detection. 
OLIVE-SIDED FLYCATCHER 
(Nuttallornis borealis) 
(Fig. 46 and 47) 
Spring Migration 
The olive-sided flycatcher is a regular migrant 
throughout Illinois in the spring and fall. Its arrival in the 
spring is usually in early May (Fig. 48). The earliest 
recorded date for the state is April 29 for central Illinois 
(Smith 1930). It has been recorded in the St. Louis area 
on April 30 (Cooke 1888) and May 2 (Anderson 1962). 
The spring migration of the olive-sided flycatcher 
regularly extends into June even in southern IIlinois (Fig. 
48), making it one of the latest spring migrants in the 
state. The earliest credible record for northern Illinois is 
May 3 (Smith 1942). The lastest date of occurrence in the 
spring is June 18 at Deerfield in northern IIlinois (Boulton 
& Pitelka 1938). 
Olive-sides often sing in migration even in southern 
Illinois. The song is a quickly delivered “hic-three-beers.” 
Often they give characteristic “ter, ter, ter” or “pip, pip, 
pip” calls. We most often have seen olive-sides, singly, 
perched on dead branches near the tops of tall trees at the 
edges of clearings. 
Fall Migration 
This species is among the first northern passerine 
migrants seen in I]linois in late summer. The olive-sided 
flycatcher appears in the Chicago area as early as August 
9 (Ford 1956). They reach even southern Illinois by the 
third week in August. There is a July 6 date for northern 
Illinois (Ford 1956), and Nelson (1876-1877) felt that the 
species possibly bred in the state because of June records 
(Fig. 48). However, until nesting is actually observed 
these June-July records must be regarded as spring 
stragglers or early “fall” arrivals. The closest known 
breeding population of olive-sides is in Wisconsin (Fig. 
47). Peak numbers in the fall occur in early and 
mid-September (Fig. 48). Total numbers seen by the 
authors were slightly more in the fall than in the spring 
(1.3 to 1.0). The latest date we have for the species is 
October 5 in southern Illinois (Fig. 48). 
In our spring censuses far more birds of this species 
were seen on the eastern side of the state than on the 
52 
Fig. 46. — Drawing of olive-sided flycatcher. This species is d 
color, like the wood pewee, but larger and with heavy gray shadi 
its sides. 
western side (4.4 to 1.0). In the fall this is also true 
the ratio is about 2.7 in the east to 1.0 in the 
Although the olive-sided flycatcher is considered so 
in its habits, Gault (unpublished notes) often saw 
together (a pair?) in spring. Once he observed tha 
such birds were ‘“quarrelsome with each other.” I 
fall several (as many as five) may occasionally be 
together and may represent family groups. They d 
generally occur in other bird flocks. The largest nu 
seen by the authors at any one time was 10 in 2} 
September 7, 1957 in central Illinois. 
