Evans Ogden el al. • WREN BREEDING ECOLOGY VARIES WITH ELEVATION 
275 
pairs at low elevation were fledging their first 
broods. 
Pacific Wrens produced fewer offspring with 
lower mass at high elevation compared to lower 
elevation, in contrast to fecundity patterns ob¬ 
served for Dark-eyed Juncos (Bears el al. 2008. 
2009), Savannah Sparrows (Martin et al. 2009), 
and Homed Larks (Camfield et al. 2010). Pacific 
Wrens did not adjust their per capita provisioning 
of nestlings with increased elevation to compen¬ 
sate for the more rigorous conditions as observed 
for high elevation finches and tits in Eurasia 
Badyaev 1997. Lee et al. 2011). Early develop¬ 
mental and offspring growth patterns did not vary 
with elevation, and it appears that high elevation 
habitats are peripheral or sub-optimal breeding 
habitats for the Pacific Wren. 
Species that are well adapted to high elevation 
habitats exhibit increased survival to offset 
reduced annual fecundity. Horned Larks breeding 
at 1,500-1.850 m had about 18% higher annual 
survival compared to birds breeding al a lower 
elevation and latitude (Camfield et al. 2010). 
Dark-eyed Juncos breeding at 2.000 m also had 
18% higher survival compared to those at low 
elevation on the same mountain (1.000 m: Bears 
et al. 2009). Pacific Wrens had the reverse pattern 
with low survival and breeding philoputry at high 
elevation. Wrens breeding at low elevation 
experienced an annual survival of 53%, similar 
to other wren populations (Peach et al. 1995. Hcjl 
etal. 2002). However, none of the birds banded at 
high elevation returned the following year, 
suggesting either low survival or low site fidelity 
on high elevation territories. 
!l was not clear which key resources limit 
breeding for Pacific Wrens at high elevation. Nest 
xites may be limited at high elevation as they are 
predominantly associated with downed or dead 
wood (Waterhouse et al. 2002), which is limited at 
high elevation. Wrens are capable ol nesting on 
c| itt laces and other locations, and appear adapt¬ 
able in their nest site selection. One male built 
five nests on his high elevation territory, and still 
failed to attract a mate suggesting that females 
may he reluctant to settle on high elevation terri- 
"fies. Food earlier in the breeding season may be 
'uniting as insects and other invertebrates form 
'hr mainstay of their diet (Van Horne and Bader 
'WO, Hejl et al. 2002). Reduced time to breed 
within a season and greater stochasticity in environ¬ 
mental conditions al high elevations impose strong 
limits on annual fecundity, especially given the dual 
disadvantage of higher failure of first clutches and 
reduced opportunities for rc-nesting and second 
broods compared to low-elevation populations. 
We conclude Pacific Wrens lack adaptations to 
high elevation, and that upper montane and sub- 
alpine sites represent inferior breeding habitats. 
However, we observed hatch-year individuals and 
broods, indicating that a small proportion of 
Pacific Wrens bred successfully at our high 
elevations sites. Given that individuals and pairs 
also occur at high elevation elsewhere, it is 
reasonable to acknowledge that in some locations, 
years or habitat types. Pacific Wrens are able to 
reproduce successfully and survive at higher 
altitudes. 
ACKNOWLEDGMENTS 
Funding was provided lo KM by the Natural Sciences 
and Engineering Research Council (NSERC) ot Canada and 
Environment Canada (Sciences Horizons. Georgia Basin 
Ecosystem Initiative), and an NSERC Postdoctoral Fellow¬ 
ship to I .JF.O. Wc thank Stephanie Topp, Alana Demko. 
Greg Ferguson. Tracv Sutherland, and Marty Mossop lor 
field assistance. We thank B. C. Parks tor logistical support 
and access. 
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