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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 124. No. 2. June 2012 
TABLE 2. Mass, wing chord, and tarsus of adult Pacific Wrens (breeding males and females) and nestlings (at 11- 
12 days of age) across three elevations on Mount Seymour, Brilish Columbia. Canada. Means ± SE. sample sizes 
in brackets. 
Elevation 
Male 
Female Nestling 
A. Mass 
Low 
9.35 ±0.12 (32) 
8.92 ± 0.17 (21) 8.89 ± 0.20 (30) 
Middle 
8.96 ± 0.14 (7) 
8.06 ±0.06 (4) 9.01 ± 0.14(11) 
High 
9.29 ± 0.12 (18) 
9.03 ± 0.18 (10) 7.89 ±0.37 (7) 
B. Wing chord 
Low 
48.30 ±0.18 (33) 
45.40 ± 0.31 (21 ) 
Middle 
48.86 ± 0.34 (7) 
45.50 ± 0.91 (4) 
High 
47.58 ± 0.15 (17) 
46.25 ± 0.22 (10) 
C. Tarsus 
Low 
20.36 ±0.17 (33) 
19.77 ± 0.15 (21) 
20.09 ± 0.36 (4) 
Middle 
20.33 ± 0.17 (7) 
High 
20.41 ± 0.14 (18) 
20.02 ± 0.08 (10) 
Adult Morphology and Mass.— We observed 
few morphological differences among adult wrens 
breeding across elevations (Table 2). Wing chord 
and tarsus were longer for males than females 
(wing: F, m = 101.26, P < 0.001; tarsus (F,. S9 = 
8.95, P = 0.00), bin neither trait varied with 
elevation (wing: F 2%HH = 0.68. P = 0.50; tarsus: 
^2,89 — 0.32, P — 0.70). Adult mass varied with 
both sex of adult and elevation with males being 
heavier than females (F, 88 = 9.99, P = O.OOl 
wrens at middle elevations were lighter than those 
at high or low elevations (Fj-. S 8 = 3.65, P = 0.03). 
Adult mass (males and females pooled) was 
similar between low and high elevation (low: 
9.19 ± 0.10 g. /i = 53; high: 9.18 ± 0.10 g, n = 
28), but birds at middle elevations were lighter, 
especially the lour females in our sample (8 64 ± 
0-16 g, n = 11; Table 2). 
Load Adult and Juvenile Annual Survival.— 
Nine ol 28 (33.3%) adults and one of 50 (27c) 
nestlings banded at low elevation in 2003. 
returned in 2004, respectively. None of the 19 
adults and six juveniles banded at high elevation 
in 2003 was re-observed in 2004 (Table IB). 
DISCUSSION 
Pacific and Winter wrens are reported breedit 
from sea level to >3,700 m (Heijl et al. 2002). b 
we lound Pacific Wrens on our coastal mounta 
Sites in British Columbia, had lower indices , 
mating status, fecundity, nestling condition, loc 
survival, and natal and breeding philopatry at hm 
elevations. We found no differences with elev; 
don in clutch size, offspring development time: 
or per capita parental provisioning of nestlings, 
riuis, we found no evidence for changes in 
breeding ecology of Pacific Wrens with elevation 
and no support for our hypothesis of a shift to a 
'slower' life history with increasing elevation. 
I his contrasts to several recent studies ol 
songbirds breeding across elevation gradients in 
western North America such as Dark-eyed Junco 
(./unco hvenuilis). Savannah Sparrow ( Passercu- 
Ins sandwichensis), and Homed Lark (Eremophila 
alpestris anicola) (Bears et al. 2009. Martin et al. 
2009. Cam fie Id et al. 2010). 
Hie avian breeding season at high elevation can 
lx* about 60% shorter than at lower elevations. 
Dark-eyed Juncos breeding at 2.000 m in Jasper 
National Park, Alberta had a 59% reduction in 
seasonal duration of clutch initiation compared to 
juncos at 1,000 m in the same area (40 vs. 97 days; 
Bears ct al. 2009). An alpine population of 
Horned Larks initiated clutches over an average 
period of 38.5 days, a 59% shorter duration than 
the 94-day clutch initiation period for a low 
elevation population (Camfield et al. 2010). 
Juncos and alpine populations of larks and 
Savannah Sparrows all had normal or high 
survival of eggs, hatchlings, and fledglings 
(Martin ct al. 2009). The clutch initiation period 
lor Pacific Wrens breeding at high elevation was 
61% shorter than for wrens breeding at lower 
elevation on the same mountain: thus, there was 
only sufficient time to produce one brood/season 
at high elevation. The high elevation territories 
still had deep snow present with some females not 
yet. or only just arriving, at the same time that 
