Volume 44, No. 1

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Ashy Storm-Petrel Oceanodroma homochroa mist-netting and capture rates in the California Channel Islands, 2004-2007




ADAMS, J. 2016. Ashy Storm-Petrel Oceanodroma homochroa mist-netting and capture rates in the California Channel Islands, 2004-2007. Marine Ornithology 44: 71 - 82

Received 28 May 2015, accepted 22 December 2015

Date Published: 2016/04/15
Date Online: 2017/02/28
Key words: Ashy Storm-Petrel, Oceanodroma homochroa, mist-netting, Channel Islands, catch-per-unit-effort, standardized monitoring, population trends


The California Channel Islands (CCI) provide essential nesting habitat for a significant portion of the world's Ashy Storm-Petrel Oceanodroma homochroa (ASSP) breeding population, but true abundance at this locality is not well known. Land-based nocturnal mist-netting has been conducted sporadically in the CCI since 1976, with variation in techniques and methods. Using a standardized catch-per-unit-effort (CPUE) is one of the few methods available to monitor trends in relative abundance, but there currently are no guidelines for a standardized, repeatable approach for the CCI. During 2004-2007, I conducted mist-netting for ASSP at three colony sites within the CCI: Scorpion Rock (SR), Santa Barbara Island (SBI), and Prince Island (PI). During 47 site-nights (22 sessions), I obtained 1 177 unique captures, including 34 recaptures (2.9%) of previously banded individuals. ASSP captured at all three islands showed peak proportions of fully developed incubation patches in July and August. ASSP captured in the CCI had 5%-9% lower body mass than individuals captured off central California during the early 1970s; it is not known whether this difference reflects natural inter-annual variation or differences in body condition. ASSP from SBI had the lowest body condition index (BCI) compared with those from PI and SR, indicating different foraging environments. Overall, 22 netting-sessions at three islands yielded a power of 84% to detect a 30% lesser CPUE; 19 sessions would be required in a future effort to evaluate this level of change. Evaluation of additional factors that affect CPUE and other independent measures of abundance or attendance should be included in future mist-netting efforts.


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