Browsing by Author "Bak, Trevor"

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    2021 Tinian Island forest bird abundance estimates
    (2022-05-26) Camp, Richard J.; Bak, Trevor; Genz, Ayesha S.
    The U.S. Navy, through Micronesian Environmental Services, surveyed landbirds in the Military Lease Area on Tinian Island in May and June 2021 using point-transect distance sampling methods. There were 2,074 individuals of 14 species detected during 123 point counts. Six species were detected during >50% of the counts and were observed at relatively high abundances, while eight species occurred at <50% of the counts and were uncommon to rare. Densities of native landbirds in the Military Lease Area ranged from the uncommon Mariana kingfisher (Todiramphus albicilla) at 0.46 birds/ha (95% confidence interval [CI] = 0.33–0.63) to the very abundant bridled white-eye (Zosterops conspicillatus) at 102.63 birds/ha (95%CI = 86.70–122.91). Most distances recorded during the 2021 Military Lease Area survey were rounded to distance intervals of 0 and 5. Measuring exact distances of detected animals is preferable to collecting distances grouped into bins or rounding. Direct comparison with previously published estimates was not possible because of changes in the sampling frame; however, densities of six species were greater, two were smaller, and one was similar to the 2008 survey estimates for the Hagoi, Diablo, and Masalog regions. Our findings indicate that the landbird community in the Military Lease Area appears to be dynamic and resilient.
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    A Global Ecological Signal of Extinction Risk in Marine Ray-Finned Fishes
    (2022-05) Bak, Trevor; Knope, Matthew; Tropical Conservation Biology & Environmental Science
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    Nihoa and Laysan Island passerines population abundances, trends, and habitat utilization
    (2024-06-18) Bak, Trevor; Camp, Richard; Farmer, Chris; Rounds, Rachel; Plentovich, Sheldon; Vetter, John; Banko, Paul; Nash, Sarah
    Nihoa and Laysan Island, part of the Northwestern Hawaiian Islands, are host to three endangered passerine species—Nihoa finch (Telespiza ultima), Nihoa millerbird (Acrocephalus familiaris kingi), and Laysan finch (Telespiza cantans). Using point-transect distance sampling survey records from 2010 to 2022 for Nihoa and 2013 to 2019 for Laysan Island, we estimated the density and abundance of all three species. We also compared densities between habitats for both islands, classifying Nihoa habitat as Eragrostis (grass) or mixed shrub and Laysan Island as open or dense habitat. The population of Nihoa finch remained stable with slight fluctuations among years, with a population size of 6,592 (4,954–8,655) birds for the most recent sampling year, 2022. Laysan finch also remained stable with a total population in both dense and open habitat of 17,657 (11,994–23,320) for the most recent sampling year, 2019. The Nihoa millerbird significantly increased on both Nihoa and Laysan Island with a global population of 1,907 (1,291–2,766) in 2019, the most recent year both islands were sampled. Overall, the populations of these three endangered species were stable or increasing. The increase of Nihoa millerbird on Laysan Island, after being translocated to the island in 2011 and 2012, represents the successful establishment of a second viable population, leading to a decrease in the species’ IUCN extinction risk status (from critically endangered to endangered). Continued population monitoring of these endangered species can help inform future management actions and ensure their preservation into the future.