Evans Ogden el al. • WREN 
BREEDING ECOLOGY VARIES WITH ELEVATION 
differ. We expected Pacific Wrens breeding at 
high elevation to show a shift to a slower lifestyle 
with lower annual fecundity and higher survival. 
METHODS 
Study Species —Pacific Wrens breed across 
extensive elevation gradients in western North 
America from the Alaskan Pacific Coast to central 
California and inland to Alberta, western Mon¬ 
tana. and central Idaho (Chesser et al. 2010). They 
are typically associated with conifer forests, but 
will nest in mixed forests, on cliff faces, and in 
npanan habitats. Pacific Wrens use a range ol 
types of nest sites and styles of nest construction. 
They are often cavity nesters. excavating holes in 
the root masses of upturned trees or in decaying 
trees or downed logs, but will also construct non- 
cavity nests in tree branches or riparian vegetation 
(Waterhouse et al, 2002). Males arrive early in 
breeding areas to establish territories and begin 
constructing multiple nests with females arriving 
shortly after to select a nest from the newly 
constructed or older nests present on the territory. 
Females typically lay one egg/day and complete 
dutches of five to seven eggs. Only females 
incubate eggs which hatch 14-16 days after onset 
of incubation. Males and females provision 
nestlings that usually remain in the nest 15- 
19 days before fledging. Pacific Wrens may raise 
two broods per season (Hejl et al. 2002). No blood 
parasites were found in adult or nestling Pacific 
Wrens at any elevation in coastal montane coni¬ 
ferous forests in British Columbia (Topp ct al. 
2007). 
Study Area and Field Methods .—This study 
was conducted over two breeding seasons, May to 
August. 2003-2004 at Mount Seymour Provincial 
(“ark in the coastal mountain range ol southern 
British Columbia, Canada -15 km NE of 
Vancouver (49 23’ N, 122 56' W). The study 
area encompassed two biogeoclimalic /.ones with 
■ow elevation sites (100-500 m) within the 
Coastal Western Hemlock (Tsuga heterophylla) 
zone, and high elevation sites (750-1.300 m) 
within the subalpinc Mountain Hemlock ( T . 
toertensiana) zone. We also collected field data 
at mid elevation (550-700 m) for several 
Enables. The Coastal Western Hemlock /.one 
has a mean annual temperature ol —08 C and, in 
summer, temperatures arc typically >10 C 
(Pojar et al. 1991). The mean annual temperature 
lor the Mountain Hemlock zone is ~0 C with 
temperatures >10 C only from mid-June 
through August. 
We searched for. captured, and color-banded 
adults and juveniles during 2003-2004 and 
monitored active nests (nests that contained 1 or 
more eggs or nestlings) and potential nests (nests 
from previous years in good condition, nests 
under construction, or recently constructed nests 
as indicated by the presence or addition of new 
nest materials) along an elevation gradient (100— 
1.300 m). We located Pacific Wren pairs and nests 
using a combination ol behavioral cues and 
intensive searching of potential nest sites. Males 
wore captured and banded at or near nest sites 
using mist nets and song playbacks, and most 
females were captured directly off the nest during 
incubation using a modified butterfly net in the 
dim light just before dawn (mist-netting attached 
to a round hoop on a pole). Nestlings reach near 
Hedging mass at 10 days of age (McLachlin 1983) 
and wc banded most al 11-12 days of age. 
Search efforts for pairs and nests in 2003 were 
allocated approximately evenly across elevations 
with time and personnel divided between sites. We 
focused our efforts in 2004 only on high (750- 
1,300 m) and low (100-500 m) elevation nests to 
ensure that we obtained a sufficient sample size at 
these altitudes. Nests were discovered during 
construction, laying, incubation, and nestling 
stages. Territories were delineated based on 
presence of singing males, video recordings at the 
nest, and on mapped locations of active and 
potential nest sites. Locations of color-banded 
males were tracked throughout the breeding season 
using song playbacks to assign males to territories. 
Nests were visited about every 3 days to record 
nest status and fate, Clutch size and nestling 
number were ascertained with visual counts using 
dental mirrors and flashlights. Temperature log¬ 
gers (HOBO Pro Series, Number H08-031-08, 
Onset Computer. Pocaset. MA. USA) were placed 
in nests during the incubation period with 
temperatures recorded at 1-min intervals to 
establish nest attendance patterns. This allowed 
us to obtain precise estimates of the time of 
nesting failure. Video cameras were placed 5 to 
10 m from nests during the nestling period and 
focused on the nest entrance to record parental 
provisioning and brooding time behavior. All 
parental activity near nests within 2-hr video 
sessions was recorded and later transcribed by 
viewing video tapes to summarize the number of 
provisioning trips/adult/hr. 
