Tase 3.— Breeding populations of catbirds in various Illinois habitats. 
: Birds Per ; Type of Region or 
ae aoe 100 Acres* eo Census County pr ecuce 
Edge shrubbery 15 150 1957-1958 Strip North Graber & Graber 1963 
21 Sy Central 
22 5 South 
Thickets i/ 226 1937 Nest Lake (N) Beecher 1942 
| 13 46 1950 Nest Jackson (S) Brewer & Hardy 1950 
tarly shrub ty 72 1966 Nest Vermilion (C) Karr 1968 
uate shrub xi 52 1966 
3lock shrub areas 32 Ml 1957-1958 Strip North Graber & Graber 1963 
49 14 Central 
107 1 South 
Irchard 36 5 1957-1958 Strip North Graber & Graber 1963 
78 3 South 
econd growth or cut-over woods 15 86 1937 Nest Rock Island (N)  Fawks 1937 
iS 106 1938 Fawks 1938 
56 TDS 1941-1944 Nest Sangamon (C) Robertson 1941, 1942, 1944 
46 DAY, 1948 Robertson & Snyder 1948 
‘irgin floodplain forest 77 3 1948 Nest Sangamon (C) Snyder, et al. 1948 
razed bottomland 93 6 1955 Nest Macon (C) Chaniot & Kirby 1955 
orest (all types including edge) 177 2 1957-1958 Strip North Graber & Graber 1963 
214 7 Central 
340 48 South 
orest edge 55 0-7 1927-1948 Nest Champaign (C) Kendeigh 1944, 1948 
55 (0-12 per mile) 1949-1968 Nest Champaign (C) Kendeigh & Fawver QBS). 
Kendeigh & Forsyth 1959, 
Kendeigh & Barnett 1968 
fodified woodland 28 43 1937 Nest Lake (N) Beecher 1942 
arkland estates 100 16 1915 Nest Cook (N) Eifrig 1915 
esidential areas 160 1 1958 Strip North Graber & Graber 1963 
75 4 Central 
98 22 South 
8 75 1915 Nest Richland (S) Cooke 1916 
vampy prairie 67 550 1941-1944 Nest Sangamon (C) Robertson 1941, 1942, 1944 
* We have converted all figures to read birds per 100 acres or birds per mile of edge (number of territorial males or nests < 72) 
> Less than one. 
For our sample of nests in northern and central IIli- 
is, Clutches averaged 3.7 eggs in May and June, and 
1 in July and August (Table 5). Cowbird parasitism 
catbirds is apparently rare. The one Illinois record we 
1ow of was in a nest observed by Goelitz (1915). 
Nehrling (1880) and Schantz (1931) believed that 
tbirds regularly produced two broods a year, but there 
€ no observations on banded birds either to substantiate 
refute their view. The laying curve for catbirds in Ili- 
is (Fig. 12) has several peaks, much like that of the 
ockingbird, but very different from the high-peaked 
aph for the thrasher. Most of the egg production comes 
May and June (Fig. 12). (For an illustration of the 
st and eggs, see Fig. 14.) 
Nesting success of the catbird (Table 6) was quite 
nsistently higher than that of the thrasher. In north- 
Stern Illinois in late summer about two-thirds of the 
38 laid produced fledglings (Table 6). The only other 
cess data available for catbirds in Illinois are those 
Finley (1917) who found that catbirds had the highest 
cess (about 65 percent of eggs produced fledglings) 
of the common species on the Normal School campus at 
Macomb. 
We can offer no reason for the catbird’s high nesting 
success, compared with that of the other mimids, and 
there are few observations on the causes of nest failure 
in this species. Only about 2 percent of eggs in northern 
Hlinois failed to develop embryos. Thompson (1958) and 
Baroody (1938) reported attacks by blue jays (Cyanocitta 
cristata) on catbird nests in northern and southern IIlj- 
nois, and Ridgway (1921) observed a gray squirrel (Sciu- 
rus carolinensis) destroying a catbird brood in the south. 
Fall Migration 
In August and early September many if not most 
catbirds are in molt and their appearance is ragged. We 
have seen a few still molting heavily as late as September 
22 in central Illinois, but many catbirds appear to have 
completed molting by September 10 and we have seen 
catbirds in fresh plumage as early as August 17. 
When the fall migration of catbirds actually begins 
is unknown. Recorded departure dates from IIlinois range 
ie) 
