Mating and Breeding Success Decline with Elevation for the Pacific Wren (Troglodytes pacificus) in Coastal Mountain Forests Author(s) :Lesley J. Evans Ogden, Michaela Martin, and Kathy Martin Source: The Wilson Journal of Ornithology, 124(2):270-276. 2012. Published By: The Wilson Ornithological Society DOI: http://dx.doi.org/10.1676/11-186.1 URL: http://www.bioone.org/doi/full/10.1676/11-186.1 BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/ terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. The Wilson Journal of Ornithology 124(2):270–276, 2012 MATING AND BREEDING SUCCESS DECLINE WITH ELEVATION FOR THE PACIFIC WREN (TROGLODYTES PACIFICUS) IN COASTAL MOUNTAIN FORESTS LESLEY J. EVANS OGDEN,1 MICHAELA MARTIN,1,2 AND KATHY MARTIN1,3,4 ABSTRACT.—We studied the population ecology of Pacific Wrens (Troglodytes pacificus) in 2003 and 2004 breeding across elevations from 100 to 1,300 m in coastal mountain forests in southwestern British Columbia, Canada to examine if this species is adapted to upper montane and subalpine habitats. We found fewer territories at high elevation, a higher proportion of unmated males, fewer nests per mated male, and no returns of banded adults or juveniles. The breeding season was 61% shorter (31 vs. 79 days), and mass of nestlings (at 11–12 days of age) and nest survival were lower at high elevation compared to lower elevation sites. Clutch size, incubation and nestling periods, parental provisioning rates of nestlings, and adult morphology did not vary with elevation. Annual fecundity measures declined with increasing elevation with no apparent compensatory increases in other vital rates such as survival of adults or offspring. Received 27 October 2011. Accepted 23 December 2011. The Pacific Wren (Troglodytes pacificus), a ability to initiate nesting was influenced by snow- small migratory songbird that breeds in coastal melt phenology (Martin and Wiebe 2004, Martin coniferous forests of western North America, was et al. 2009, Wilson and Martin 2010). Birds recently described as a species distinct from the breeding at high elevations appear to compensate Winter Wren (T. hiemalis) in the rest of North for reduced annual fecundity by increasing their America and the Eurasian Wren (T. troglodytes) per capita parental care, thus improving juvenile in Europe (Wesolowski 1983, Toews and Irwin survival (Badyaev and Ghalamor 2001). Body 2008, Chesser et al. 2010). Pacific Wrens are size of adults and egg size both increase with common birds of northern temperate coniferous increasing elevation (Bears et al. 2008, Zeng and and mixed forests of North America, but there are Lu 2009, Lu et al. 2010). Several songbird species few studies of their breeding ecology and nesting trade reduced annual fecundity for increased success (McLachlin 1983, Van Horne and Bader survival of both adults and young in high 1990, Waterhouse 1998, De Santo et al. 2003). elevation populations (Bears et al. 2009, Martin The Pacific Wren breeds across an elevation et al. 2009, Camfield et al. 2010). These studies gradient from sea level to upper montane and found intra-specific differences with elevation as subalpine habitats along the west coast of North high elevation populations shifted to a ‘slower’ America (Toews and Irwin 2008). life history with a longer life span, fewer offspring High mountain areas are characterized by per breeding season, but greater investment in variable weather, cold temperatures, and short parental care. The length of the breeding season breeding seasons (Martin 2001). At least 90 bird sharply decreases with increasing elevation due to species breed across wide elevation gradients, later snow melt and shorter vegetative growth some of which range from sea level to alpine seasons, and birds increase their per capita habitats, but their ecology, behavior, and life parental investment. Birds at higher elevations history at upper elevation limits are poorly are larger, heavier, and have higher survival understood. Short breeding seasons at high (Bears et al. 2009, Martin et al. 2009, Camfield elevations translated into lower annual fecundity et al. 2010). for the few species studied, particularly when the We investigated variation in the breeding ecology of the Pacific Wren along an altitudinal 1 Centre for Applied Conservation Research, Department gradient from 100 to 1,300 m. We predicted that of Forest Sciences, 2424 Main Mall, University of British as elevation increased: (1) breeding season Columbia, Vancouver, BC V6T 1Z4, Canada. duration, the number of broods, and/or clutch 2 Centre for Wildlife Ecology, Department of Biological size would decrease; (2) duration of incubation Sciences, Simon Fraser University, Burnaby, BC V5A 1S6, and nestling periods would increase; (3) per capita Canada. 3 Environment Canada, 5421 Robertson Road, Delta, BC parental care of nestlings and offspring mass at V4K 3N2, Canada. fledging would increase; (4) birds would have 4 Corresponding author; e-mail: [email protected] higher survival; and (5) mating status would not 270 Evans Ogden et al. N WREN BREEDING ECOLOGY VARIES WITH ELEVATION 271 differ. We expected Pacific Wrens breeding at temperatures .10 uConlyfrommid-June high elevation to show a shift to a slower lifestyle through August. with lower annual fecundity and higher survival. We searched for, captured, and color-banded adults and juveniles during 2003–2004 and METHODS monitored active nests (nests that contained 1 or Study Species.—Pacific Wrens breed across more eggs or nestlings) and potential nests (nests extensive elevation gradients in western North from previous years in good condition, nests America from the Alaskan Pacific Coast to central under construction, or recently constructed nests California and inland to Alberta, western Mon- as indicated by the presence or addition of new tana, and central Idaho (Chesser et al. 2010). They nest materials) along an elevation gradient (100– 1,300 m). We located Pacific Wren pairs and nests are typically associated with conifer forests, but using a combination of behavioral cues and will nest in mixed forests, on cliff faces, and in intensive searching of potential nest sites. Males riparian habitats. Pacific Wrens use a range of were captured and banded at or near nest sites types of nest sites and styles of nest construction. using mist nets and song playbacks, and most They are often cavity nesters, excavating holes in females were captured directly off the nest during the root masses of upturned trees or in decaying incubation using a modified butterfly net in the trees or downed logs, but will also construct non- dim light just before dawn (mist-netting attached cavity nests in tree branches or riparian vegetation to a round hoop on a pole). Nestlings reach near (Waterhouse et al. 2002). Males arrive early in fledging mass at 10 days of age (McLachlin 1983) breeding areas to establish territories and begin and we banded most at 11–12 days of age. constructing multiple nests with females arriving Search efforts for pairs and nests in 2003 were shortly after to select a nest from the newly allocated approximately evenly across elevations constructed or older nests present on the territory. with time and personnel divided between sites. We Females typically lay one egg/day and complete focused our efforts in 2004 only on high (750– clutches of five to seven eggs. Only females 1,300 m) and low (100–500 m) elevation nests to incubate eggs which hatch 14–16 days after onset ensure that we obtained a sufficient sample size at of incubation. Males and females provision these altitudes. Nests were discovered during nestlings that usually remain in the nest 15– construction, laying, incubation, and nestling 19 days before fledging. Pacific Wrens may raise stages. Territories were delineated based on two broods per season (Hejl et al. 2002). No blood presence of singing males, video recordings at the parasites were found in adult or nestling Pacific nest, and on mapped locations of active and Wrens at any elevation in coastal montane coni- potential nest sites. Locations of color-banded ferous forests in British Columbia (Topp et al. males were tracked throughout the breeding season 2007). using song playbacks to assign males to territories. Study Area and Field Methods.—This study Nests were visited about every 3 days to record was conducted over two breeding seasons, May to nest status and fate. Clutch size and nestling August, 2003–2004 at Mount Seymour Provincial number were ascertained with visual counts using Park in the coastal mountain range of southern dental mirrors and flashlights. Temperature log- British Columbia, Canada ,15 km NE of gers (HOBO Pro Series, Number H08-031-08, Vancouver (49u 239 N, 122u 569 W). The study Onset Computer, Pocaset, MA, USA) were placed area encompassed two biogeoclimatic zones with in nests during the incubation period with low elevation sites (100–500 m) within the temperatures recorded at 1-min intervals to Coastal Western Hemlock (Tsuga heterophylla) establish nest attendance patterns. This allowed zone, and high elevation sites (750–1,300 m) us to obtain precise estimates of the time of within the subalpine Mountain Hemlock (T. nesting failure. Video cameras were placed 5 to mertensiana) zone.