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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 124. No. 2. September 2012 
TABLE I. Significant population and environmental factors affecting Eastern Screech-Owls nesting in suburban 
central Texas based on annual data during 1980-2009 evaluated by Principal Components (PC) analysis. Factors are listed 
in order of their highest (top) to lowest sums of PC scores regardless of sign. The proportion of each PC's explained 
variance is in parentheses (total 11%). 
Factor* 
PC 1 (39%) 
PC It H7%) 
PC III (12%) 
PC IV (9% i 
Number of nests 
0.49 
-0.36 
0.55 
0.33 
Mean first egg date 
-0.05 
0.23 
0.62 
-0.26 
Females > 2 years of age 
0.14 
-0.03 
-0.05 
0.81 
Pairs of nesting birds (food) 
-0.11 
0.37 
0.17 
0.18 
Mean Jan-Feb temperature" 
0.32 
-0.19 
-0.15 
-0.12 
Fledglings/eggs (productivityi 
-0.17 
0.41 
0.07 
— 0.11 
Mean annual temperature 
0.38 
-0.05 
0.11 
0.03 
Mean Apr-May temperature 1 ' 
0.07 
0.03 
0.03 
0.32 
Suburban growth (sprawl) 
0.06 
0.18 
-0.06 
-0.08 
Percent successful nests 
-0.04 
0.29 
-0.02 
0.07 
“ Pre-nesting period. 
' Nestling-fledgling period. 
Doves (Zenoitla asiatica) first eaten in 1981 by 
nesting owls and Cooper’s Hawks in yards. 
Suburban Eastern Screech-Owls capture more 10- 
150-g birds than mammals (Marzluff et al. 1998), 
and birds in this size range such as doves. Northern 
Cardinals {Cardinalis cardinalis), and House Finch¬ 
es (Carpodacus mexicanus) visited feeders at dusk 
when nesting adult screech-owls begin hunting 
(Gehlbach 2008). Remains of these three species 
were among others in owl nests. 
Earlier nesting is also advantageous because of 
the longer nocturnal owl-activity period, when 
disturbance is less likely because of reduced or no 
residential yard and garden maintenance, outdoor 
play, and construction (pers. obs.). Moreover, there 
is potentially less competitive impact front relum¬ 
ing migratory hawks until April (pers. obs.). Nests 
are more likely to be disturbed, as human use of 
yards increases later in the season, but begging 
nestlings and fledglings in April-May were not 
abandoned in contrast to eggs (Gehlbach 2008). 
The decrease in nest density in early years, 
coincident with increasing sprawl, probably 
resulted from lost natural forest and more 
disturbance from building and street construction, 
The remaining forest was not fully protected until 
the last decade of study, when abundance of the 
plot s nesting birds stabilized together with sprawl 
(Gehlbach 2005). Leg bands of screech-owls 
banded as fledglings on the plot and returned 
from outside areas up to 144 km distant, 
numbered 0.2 per year before 2000 in contrast 
to 0.7/year afterward, possibly reflected the last 
decade of highest nest productivity. 
ACKNOWLEDGMENTS 
Baylor University supported this study. The Sugar Creek 
Homeowners' Association allowed use of its private nature 
preserve ol ravine-slope woodland and riparian forest. 
Several ol my college students helped with field work, My 
biologist wife, Nancy, was the principle help at nests during 
handing. She read the manuscript with five decades of 
practical experience and made suggestions throughout. 
W. E. Stout and James Ward also read the manuscript 
LITERATURE CITED 
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Bird. D M.. d. e. Varland. and J. J. Negro. 1996. 
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