SHORT COMMUNICATIONS 
385 
since 1988 (Lowther 1996) and found differences 
in clutch size in comparing average measures of 
breeding activity between 'normal' and ‘small' 
nest boxes in use at this site. My objective in this 
study is to examine and describe relationships 
which may exist of nest-box size with several 
measures of nesting activity and breeding success. 
METHODS 
I placed seven nest boxes on the garage at my 
residence in Homewood. Cook County. Illinois. 
USA, in October and November 1987. I added to 
this number in successive years to have 10 nest 
boxes in 1989. 15 in 1990, 17 in 1992 and. since 
1993. between 20 and 25 nest boxes available. 
Nest boxes were built with scrap lumber follow¬ 
ing the general design for ‘bluebird* boxes and 
most have outside measurements of -10 X 15 cm 
basal area. 20 cm height, and a 3.8 cm diameter 
entrance hole. Entrance holes were on the ‘front* 
or 'side' of the nest box and most were south- 
facing. These nest boxes were placed between 
1.7 and 2.4 m above ground and. once placed, 
generally maintained their position and specific 
identity from year to year. Removals and minor 
position adjustments (i.e., changing height above 
ground <20 cm) were made generally in response 
to predation by common raccoons (Procyon Intor) 
or cats (Feiis catus ): repairs were made as needed. 
General nest box maintenance, cleaning, and nest 
removal was conducted in September or October. 
I use the term 'nest box' primarily to refer to an 
actual nest box placed at a unique position or 
coordinate on or near the garage. (In field notes, a 
single, physical nest box used in 2 positions would 
receive 2 different ‘nesi box' designations; 2 nest 
boxes used in single position [e.g., replacement 
tor a damaged nest box| would still have the 
designation of a single ‘nest box’). Nest boxes 
have been placed at 34 unique locations since 
the 19X8 breeding season: nest boxes at these 
locations have been available for one to 24 
seasons through 201 I. Internal dimensions of the 
70 nest boxes present during the 2011 season were 
measured in September 2011. Internal dimensions 
of nest boxes at the remaining locations were 
obtained from field notes regarding nest box 
movements or nest measurements. Base urea for 
nest boxes with known internal measurements 
ranged from 112.1 cm 2 (9.5 X 11.8 cm) to 
221.2 cm 2 (11.4 X 19.4 cm). 
Nest boxes were chocked every 2 or 3 days 
during the breeding season to allow documenta¬ 
tion of dates of egg laying, hatching, nest losses, 
and young birds leaving the nest. Eggs were 
measured on their first appearance. Young were 
measured during each nest check until — 10 days 
of age and banded when reaching 15-20 g with 
IJ.S. Geological Survey bands. Mass of surviving 
young at age 7 days, from the measurement made 
at 7 days or estimated from measurements on days 
bracketing 7 days, was used as an index of nestling 
quality. 1 calculated overall mean clutch size, 
hatching success, surviving brood size, mean egg 
mass, and mean mass ol young at age 7 days for all 
nesting attempts within each nest box (with >1 
season of data). Nest attempts with completed 
clutches ranged from 17 (over S yrs) to 64 (over 
22 yrs) for the 23 nest box locations with known 
internal measurements and which were used in 
analysis; nest attempts for the 11 nest box locations 
not used ranged from 0 (over 1 yr) to 23 (over 
9 yrs). Pearson product-moment correlation coef¬ 
ficients were calculated to provide a measure of 
association between nest-box basal area and 
measures descriptive of breeding activity. 
Almost all surviving nestlings were banded and 
some efforts were made to band and color mark 
other young and adults. Efforts to identity 
individual parents for each nesting attempt have 
been considered loo disruptive and have not been 
done. Incidental observations allow association ol 
some adults with specific nest boxes and unique 
characteristics of some eggs or clutches suggest 
that particular females retain nest boxes within 
and between seasons (see also Anderson 2006). 
RESULTS 
There was a significant, positive relationship ol 
clutch size w-ith basal area of the nest box (r = 
0.592. df = 21, P < 0.0029; Fig. I). This same 
positive and statistically significant relationship 
holds if. instead, clutch size of individual nesting 
attempts was used rather than each nest box’s 
overall mean clutch size: r — 0.118, df = 893, 
p < 0.001. The difference in mean clutch size 
between smallest and largest nest boxes was 
almost 0.3 eggs: mean clutch size in nest box G23 
(basal area 112.1 cm 2 ) was 4.49 eggs (based on 36 
clutches over 13 years), mean clutch size in nest 
box GI0 (basal area 221.2 cm 2 ) was 4.77 eggs 
(based on 52 clutches over 22 years). The greatest 
mean clutch size (Fig. 1) was associated with nest 
box G19 (with base area of 144.0 cm 2 ). This nest 
box accounted for almost all (6 of 7) of the 7-egg 
clutches recorded in this study; apparently, from 
