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

Released: 2016
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.

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 mistnetting
has been conducted sporadically in the CCI since 1976, with variation in techniques and methods. Using a standardized catch-perunit-
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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This product is associated with the following project:
Research and Restoration in the California Channel Islands

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