Nesting season ecology of marbled murrelets at a remote mainland fjord in southeast Alaska Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/rv042z294

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  • This thesis focuses on the nesting ecology and marine space use of Marbled Murrelets (Brachyramphus marmoratus) during the 2007 and 2008 nesting seasons in and around Port Snettisham, a remote mainland fjord in Southeast Alaska. Marbled Murrelets (murrelets) are a declining species throughout most of their range, and their conservation is a challenging endeavor because they rely on relatively large expanses of terrestrial habitat for nesting and marine habitat for food. Murrelets are especially difficult to study because they place their nests at variable and often considerable distance from the sea in largely inaccessible locations; consequently, we know relatively little about their breeding ecology and overall life history compared to other seabirds. I used radio-telemetry to gather data on reproduction, behavior, and at-sea locations of murrelets. Herein, I describe individual and population-level marine space use, identify nesting habitat, estimate reproductive success, and characterize patterns of nest visits. Mean marine home range size for adult murrelets was significantly larger in 2008 (158.6 ± 103.7 km²) than 2007 (97.8 ± 59.4 km²), suggesting that foraging conditions were relatively poor in 2008. Similarly, mean commuting distance from at-sea location to nest sites was significantly longer in 2008 (20.0 ± 2.0 km) than 2007 (12.0 ± 0.9 km), and murrelets nesting further from the coast likely reduced their foraging ranges in 2008. Central foraging hot spots were identified throughout Port Snettisham and near Holkham Bay and Tracy Arm to the south. Boundaries of these hot spots can be used to guide management of commercial fishing and tourism, and designation of marine protected areas. I located 33 active nests in mostly inaccessible sites within forest and non-forest habitat, including visually confirmed nest sites on the branches of large conifer trees and on ledges of steep cliffs near water (e.g., waterfall, lake, river, or glacier). Widespread use of rock cliff and subalpine nesting habitats (≥ 48.5% of located nests) indicated that nesting habitat models in Southeast Alaska should include these types of habitats. Nests were located further inland (range 1.0 - 52.0 km) and at higher elevations (range 42 - 1100 m) than previously documented in Alaska, including two nest sites > 15 km east of the USA/Canada border in British Columbia, Canada. The nesting season was ca. 113 days long (25 May - 16 September), and four late-season re-nesting attempts were documented. Apparent fledge success, derived by inference from behavior of radio-tagged adults, was 17.6% (n = 6 of 34). The low reproductive success at Port Snettisham was similar to estimates from south of Alaska, and unexpected because the area has relatively high densities of murrelets and seemingly ideal conditions for nesting. This information is noteworthy to future conservation planning because it provides evidence that murrelet reproduction may be low even when conditions for nesting are relatively good. Despite an adaptation to high adult survival, murrelet populations cannot sustain themselves with similarly low levels of reproduction. Based on my results future research should focus on monitoring regional population trends, identifying causes of nest failure, estimating adult survival rates, and identifying sources of adult mortality.
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