SHORT COMMUNICATIONS 
631 
forest. Number of nests averaged 13.1 ± 1.0 
(CV = 29.9) per year in the 1980s. decreased 
insignificantly during the 1990s and stabilized 
(CV = 12.6) at 10.7 ± 0.2 per year in the 2000s 
( 2 n r = -0.66. P = 0.0005). The closest contem¬ 
poraneous screech-owl nests in residential yards 
and forest were >46 in apart. 
First eggs were laid in March and increasingly 
earlier annually (r = —0.49. P = 0.005). Dales 
averaged 21.3 ± 1.4 March in the 1980s and 
advanced to 16.8 ±1.1 March in the 2000s </• = 
5.3, P = 0.005). Dates per year and decade were 
unrelated to distance from the nearest building, 
street, screech-owl or other raptor nest Screech- 
owl nests were >30 m from the nearest yard¬ 
nesting Cooper's Hawks (Accipiwr cooperif) and 
Mississippi Kites (Iciiniu mississippiensis). and 
the exclusively forest nesting Broad-winged 
Hawks (Buteo plaryptems) and Barred Owls 
{Sirix varia). 
Productivity, measured as fledglings per egg, 
increased (2° r = 0.45, P = 0.03) from 50.3 ± 
5.9% in the 1980s to 81.7 ± 5.7% in the 2000s 
(F = 15 , 5 , p = 0.0001) and was related to 
increasing mean age of repeat-nesting females (2" 
r = 0.54, P = 0.02). Female screech-owls s2 yrs 
old laid larger clutches than yearlings (4.1 1 0.7 
vs. 3.6 ± 0.8 eggs; F = 28.3, P = 0.0001) and 
were more productive (3.2 ± 1.5 vs. 2.6 ± 1.4%; 
F = 9.8. P = 0.002). Brood size increased from 
2.3 ± 0.2 to 3.6 ± 0.1 (F = 42.9. P = 0.001 ) with 
increasing female age (experience) as did percent 
of successful nests defined as 2 rl fledglings: 55.5 
± 4.1 to 81.4 ± 2.2% (F = 15.7, P = 0.0001). 
Environmental Change and Relationships. 
Suburban sprawl advanced by 2 to 8 buildings 
annually in the first two decades (CV = 22.9) and 
stabilized (CV = 1.8) in the third decade (2° 
= 0 . 97 , p = 0.0001). Number of screech-owl 
nests tracked sprawl (r 0.85. P - 0.0001) as did 
number of experienced nesting lemales (r = 0.59. 
P = 0.009), population productivity (r = 0.82, 
P = 0.0001), and percent of successful nests (r = 
0.71, P = 0.0002) which peaked at 93% during 
2000-2009. 
Mean annual air temperature increased from 
16.7 to 20.4 C during the first two decades {r - 
0.75, P = 0.0001) but only 2.0 C afterward. 
Earlier mean annual first-egg dales followed 
increasingly warmer mean January-February 
(pre-nesting) temperatures (r - -0.62. P = 
0.0009). Percent successful nests and their 
productivity tracked earlier first eggs (/ 
-0.39, P > 0.02) and, separately, an increas¬ 
ingly warmer March-Aprii nestling-fledgling 
period (3" r 2= 0.58, P < 0.04). There were no 
trends or relationships in precipitation and the 
owl population. 
Cached carcasses and identifiable remains in 
owl nests represented 13 permanent and two 
summer resident avian species, each of which 
increased and stabilized with sprawl (2 r > 0.69, 
P < 0.001). Screech-owl fledgling productivity 
and nesting density were correlated annually with 
the total number of potential avian prey (r ^ 0.61, 
P < 0.001; r > 0.46. P < 0.03), whereas neither 
measure related to numbers of other raptor nests 
by species or collectively. 
Ten significant population and environmental 
factors that explained the suburban ecosystem 
included five of each type (Table 1). Earlier eggs 
laid by older, more productive females were the 
principal population factors, while potential avian 
food and warmer pre-nesting and nestling-fledg¬ 
ling period temperatures were the leading envi¬ 
ronmental factors. The added warmth of suburban 
sprawl was the fundamental environmental factor 
followed by increased avian prey. 
DISCUSSION 
Increasing thermal and resulting biological 
effects on pre-nesting screech-owls in January- 
February may include earlier available ectothermic 
prey such as insects, crustaceans, and reptiles. 
Warmer Apri 1-May periods may also promote food 
and nest productivity, as food demand is highest for 
foraging adults, growing nestlings, and dependent 
fledglings at this time (Gehlbach 2008). Feathered 
nestlings were weighed when banded within a 
week of Hedging and showed no significant 
changes in mass over the 30-year period. 
Known ectothermic prey were active earlier in 
the year and more continuously with the earlier 
warmer temperatures (Gehlbach 2008). This prey 
was more abundant in suburban yards than 
concurrently in adjacent riparian forest (Gehlbach 
2010). Suburban residences also focused avail¬ 
ability of known endothermic prey at bird feeders, 
bird baths, and artificial ponds (Gehlbach 1996, 
2005, 2008). Fifty-six percent of the screech- 
owls' nest sites in yards had nearby feeders that 
attracted prey noted in owl nests, and hall ot those 
yards had bird baths and/or artificial ponds used 
by the owls and other birds. 
Increasing temperatures were also associated with 
increasing tropical species such as White-winged 
