The Breeding Ecology and Foraging Niche of Aleutian Terns (Onychoprion aleuticus) in the Kodiak Archipelago, Alaska
The Aleutian tern (Onychoprion aleuticus) is a species of high conservation concern in Alaska due to large declines at known breeding locations since the 1960s. Due to the small population size and ephemeral behavior of this species on the nesting grounds, there is little basic biological informatio...
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| Other Authors: | , , , |
| Format: | Master Thesis |
| Language: | English unknown |
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Oregon State University
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| Online Access: | https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/xg94hx78f |
| Summary: | The Aleutian tern (Onychoprion aleuticus) is a species of high conservation concern in Alaska due to large declines at known breeding locations since the 1960s. Due to the small population size and ephemeral behavior of this species on the nesting grounds, there is little basic biological information available and data gaps have hindered the identification of potential drivers of the population decline. Significant unknowns include rates of and factors influencing nest survival, and key prey types across the breeding season. To investigate these questions, I used a combination of nest cameras and nitrogen (δ15N) and carbon (δ13C) stable isotope analysis of eggshell membranes to estimate daily nest survival, determine chick diet composition, and to estimate pre-laying female Aleutian tern diets from 2017 to 2020 in the Kodiak Archipelago, Alaska. A total of 148 nests, 105 observed using trail cameras, were incorporated into a nest survival analysis, 81 eggshell membrane samples were analyzed for stable isotope values, and 1313 photographs of prey deliveries used to assess chick diets. I used the nest survival model in program MARK to estimate daily nest survival (DNS) rates as a function of colony location, year, within-season time trends, vegetation cover categories and height, and six weather covariates. The nest survival modeling indicated that survival was higher during 2019= 2020 (2017=2018: \widehat{\beta\ }= -0.87, 95% CI -1.27, to -0.47) with a significant interaction between year and colony. Our final competitive model set also suggested that DNS increased with average vegetation height and decreased later in the season. Stable isotope analysis indicated that δ13C values were higher in 2017 than 2018-2020. Bayesian mixing models estimated that the diet composition of Aleutian terns was equally nearshore and offshore prey types, but that 2017 had a larger proportion of prey items from the nearshore community than 2018 – 2020. Isotopic biplot standard ellipse areas were the largest in 2017, indicating a ... |
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