ig. 3.—General distribution of the tree swallow. The out- 
range may include large sections in which populations of 
ecies are thin or even absent because of the nature of the 
n and paucity of suitable habitat. 
use swallows forage on the wing, it may be 
ult to differentiate migration flights from feed- 
lights. 
1 Illinois the swallows, including tree swallows, 
lly appear earliest in the river bottoms, and 
| even weeks later in adjacent uplands. The 
ber of birds also tends to be higher in bottom- 
. Tree swallows have been seen in Illinois as 
as March 11, and Nelson (1876-1877) refers 
eir arrival in numbers to northeastern Illinois 
March 20, but more typically they come in 
land May (Fig. 4). Usually, only a few birds 
een in March, and there is a small but no- 
pulse about April 1. The largest influx occurs 
mid-April to late April, with lesser peaks 
early to mid-May (Fig. 4). The migration 
extend into June some years, as Loucks 
ublished manuscript, 1892) mentioned 200 birds 
r 
> Over the Peoria area on June 11. 
bution 
he general distribution of the tree swallow is 
nin Fig. 3. The Illinois distribution (Fig. 5) 
is not well known. The present records indicate 
that most of the Illinois population is in the northern 
half of the state. Musselman (1933) hinted sthat 
the Illinois River was the principal nesting area for 
the tree swallow in Illinois, and indeed there are 
many nest records from the Illinois Valley. Sloughs 
in the Mississippi, Ohio, and Wabash bottoms of 
southern Illinois offer much habitat that looks prom- 
ising, but, in general, the southern half of the state 
has not been investigated for breeding populations 
of this species. Ridgway (1874) recorded a nesting 
population near Mt. Carmel, but no nests have been 
reported there in this century. 
Nesting Habitats and Populations 
Tree swallows nest in isolated pairs as well 
as semicolonially. The nesting habitat most often 
described is a swamp or marsh with standing dead 
trees in or near the water. In Marshall County, 
Barnes (1890) found the tree swallow confined to 
the Illinois river bottoms. 
The nest is placed in a cavity in a stump or 
dead limb. At Mt. Carmel, Ridgway (1874) noted 
that the swallows especially utilized cavities made 
by downy woodpeckers (Dendrocopos pubescens) 
and Carolina chickadees (Parus carolinensis). Tree 
swallows also readily use man-made nest boxes, 
and most of the recent nesting records are of this 
type, though tree swallows have not received nearly 
as much attention in Illinois as have bluebirds 
(Stalia sialis) and martins (Progne subis). The dis- 
crepancy may be related to the more specialized 
habitat of the tree swallow. There are several new, 
large reservoirs in the state, and nest boxes placed 
near the shores of such bodies of water may attract 
tree swallows and thus have a marked effect on the 
state population. 
The only published population measurements 
are those of Beecher (1942) who found 40 nests 
(occupied nest boxes) in about 28 acres of modified 
woodland in Lake County. He also recorded an 
extremely dense population of 20 occupied boxes 
on 100 square feet. These figures do not include 
foraging habitat, however. 
The tree swallow, like other cavity nesters, is 
confronted with the problem of competition for 
nest sites. Nelson (1876-1877) observed fighting 
over a house between martins and tree swallows, 
with the martins dominating, but Beecher (1942) 
found no strife between the two species occupying 
two houses on the same post. Ridgway (1874) 
noted apparent competition for housing between 
prothonotary warblers (Protonotaria citrea) and 
tree swallows. Barnes (1912) attributed population 
decline of the tree swallow in Marshall County 
after 1890 to competition from the house sparrow 
(Passer domesticus), and Loucks (1895) also men- 
tioned house sparrow competition with the tree 
