Evans Ogden el al. • WREN BREEDING 
ECOLOGY VARIES WITH ELEVATION 273 
200 400 600 800 1000 
B 
200 400 600 800 1000 
'5 200 400 600 800 1000 
Elevation (m) 
D 
400 600 800 1000 
Elevation (m) 
FIG. I. Breeding parameters of Pacific Wrens nesting along an elevation gradient (100-1 100 m) on Mount Seymour 
British Columbia, Canada. 2003-2004. A. Date-of-first egg (Julian date, day 1 - 1 Jan) lor all nesting attemp s. . 
size (all nesting attempts). C. Daily nest survival probability. D. Nestling feeding rates (number ol provisioning trips 
bv adults/hr). 
possible to produce a good model lor these 
fecundity data because of our small sample; but 
Hie general relationship was non-linear and 
resembled a threshold with no change up to 
4( >0 m and then a decline to zero productivity. 
Nest Survival .—The mean daily nest survival 
across elevations was 0.960 ± 0.018 (n = 46 
nests) and ranged from 0.735 to 0.983. Daily nest 
survival did not vary between years (P = 0.07, 
M model: (Dev Reside - 10.06)) and gener¬ 
ally decreased with elevation (/’ = 0.01; Fig 1C). 
All six of our active high elevation nests 
foiled, one during incubation, and five during the 
nestling stage. We encountered two families 
with fledglings and five hatch-year individuals at 
°ur high elevation site in 2003. Six hatch year 
birds were observed ‘prospecting in high 
elevation habitats (i.e„ singing a recognizably 
juvenile male song) at different locations and 
times in the autumn period. None of these hatch- 
year birds was associated with our high elevation 
nests, and none returned to breed the following 
year. 
Offspring Development Periods and Pro¬ 
visioning Rates. —Incubation (14.75 ± 0.33 days, 
„ = |2 nests) and nestling periods (17.75 ± 
0.41 days, n = 16 nests) did not vary with 
elevation (F/jo = 2.88. P = 0.12; F/ = 0.17, P 
= 0.69, respectively). Provisioning rates (number 
of trips by adults/hr) did not differ with elevation 
(F, 2 o — 0.009. P = 0.92; Fig. ID); however, 
mass of nestlings near fledging (11-12 days after 
hatching) varied with elevation (F 2 as = 3.36, P = 
0.04. Table 2). Nestling mass was similar between 
low and mid elevations (F t = 0.12. P = 0.73), 
but nestlings reared at high elevation were 
significantly lighter than those at low and middle 
elevations pooled (F IA6 = 6.74, P = 0.013). 
