Taste |.—Breeding populations of robins in various Illinois habitats. 
Birds Per, Type of Region or 
Habitat Acres 100 Acres Years Census County Reference 
lential 8 14 1916 Nest Richland (S) Cooke 1916 
20 30 1907-1909 Strip North & Central — Graber & Graber 1963 
33 36 South 
n residential 160 Sy 1957-1958 Strip North Graber & Graber 1963 
75 109 Central 
98 102 South 
and estate 100 16 OWES Nest Cook (N) Eifrig 1915 
shrub (including hedge) 15 34 IDS 7 OS Strip North Graber & Graber 1963 
21 56 Central 
22 9 South 
cet 13 4 1950 Nest Jackson (S) Brewer & Hardy 1950 
ard 45 29 1907-1909 Strip South Graber & Graber 1963 
36 5 1957-1958 North 
78 5 South 
shrub Py: 28 1966 Nest Vermilion (C) Karr 1968 
) areas 50 4 1907-1909 Strip South Graber & Graber 1963 
32 s 1957-1958 North 
49 2 Central 
126 2 South 
(all types including edge) 16 6 1907-1909 Strip Central Graber & Graber 1963 
60 iS South 
Ua) 6 1957-1958 North 
PENG) 6 Central 
337) ime South 
nland forest 12 1966 Nest Vermilion (C) Karr 1968 
edge 64 8 1943 Nest Champaign (C) Johnston 1947 
55 0-4 1927-1948 Champaign (C) Kendeigh 1944, 1948 
55 (0-20 per mile) 1949-1970 Champaign (C) Kendeigh, et al. 1950, 
Kendeigh & Barnett 1968, 
Kendeigh & Clemans 1970 
d oak-hickory forest 24 l 1967 Nest Hancock (C) Franks & Martin 1967 
| growth or cut-over woods 5 14 1937-1938 Nest Rock Island (N) Fawks 1937, 1938 
6 8-12 1941-1944 Sangamon (C) Robertson, 1941, 1942, 1944 
1 bottomland 93 6 1955 Nest Macon (C) Chaniot & Kirby 1955 
figures were converted to read birds per 100 acres or birds per mile of edge (number of territorial males or nests x 2). 
ss than one. 
hests receive either four eggs or three eggs. In April 
May, 74 percent of the nests have four-egg clutches, 
3 percent have three eggs. In June and July only 46 
nt of the nests have four-egg clutches, and 48 percent 
three eggs. In the south Klimstra & Stieglitz (1957) 
clutch size to average 3.4 eggs. Data on egg weights 
ven by Davis (1969). 
is a widely held view that robins raise two, and some- 
three broods per year. Though population studies of 
d birds are lacking for Illinois, Young’s (1955) data 
‘isconsin support this view. The egg-laying curves 
everal peaks (Fig. 4). 
obins are rarely parasitized by the cowbird 
mann 1966). We have but one record, in a sample of 
00 nests, of a single cowbird egg in a nest with three 
ggs. The host was successful in fledging young, but 
whird egg disappeared. 
There are few Illinois data on robin nesting success and 
productivity. In the nonurban population we studied in 
northwestern Illinois (Fig. 1), 58 percent of the nests and 
50 percent of the eggs fledged young in April and May 
(sample: 43 nests with complete histories), but in June and 
July (23 nests with complete histories) nesting success de- 
clined to 48 percent of the nests and 37 percent of the eggs. 
On a school campus in west-central Illinois, Finley (1917) 
found that only 39 percent of the eggs fledged young in a 
sample of 64 nests. There are no data on fledging success 
for the south, nor are there quantitative data on the causes 
of nest failures. The causes most often mentioned in the lit- 
erature or observed by us are weather (death of young from 
cold, or dislodgment of nests by wind and rain storms), and 
predation by gray squirrels (Sciwrus carolinensis), grackles 
(Quiscalus quiscula), blue jays (Cyanocitta cristata), house 
cats (Felis catus), and snakes, but the population signifi- 
