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Catch-Per-Unit-Effort (CPUE), Banding, and Morphometric Data Collected During Nocturnal Mist-Netting Sessions to Evaluate Trends and Variability Among Storm-Petrels of the California Channel Islands (1994-2018)

February 23, 2022

Herein we provide a comprehensive database of storm-petrel (Oceanodroma spp.) morphometrics, banding, and associated mist-netting data collected within Channel Islands National Park (CHIS) from 1994 to 2018. The most abundant storm-petrel species in CHIS, the ashy storm-petrel (Hydrobates homochroa; ASSP), was the focal species in most mist-netting efforts, but data also were recorded for Leach's (O. leucorhoa; Adams et al. 2016) and black (O. melania) storm-petrels. Collecting and compiling recent and historic mist-net datasets into one database has facilitated summary analyses of important components of these data including species morphometrics, recapture rates, and incubation patch condition (a potential indicator of breeding status) to better understand storm-petrel morphology, survival, and phenology in CHIS. Because this data set largely relates to ashy storm-petrel, for this species we have calculated catch-per-unit-effort (number of ASSP caught per netting minute; CPUE) to quantify inter-colony variability in attendance patterns at CHIS among years. The ability to look at such trends, and the limitations therein, highlight the value of consistent mist-netting efforts across space and time and the importance of standardized methods in future mist-netting efforts. Since 1976, researchers have conducted mist-netting efforts at several sites within CHIS during dark nights near the new moon within the ASSP breeding season (April to September) using avian mist-nets (net mesh size 30mm or 38mm size; net length 6x2.6m, 9x2.6m, 12x2.6m, or 18x2.6m) and a speaker system that broadcasted storm-petrel vocalizations (standard set of recordings used across many sites in the California Current System). Once a storm-petrel was captured in the net, it was identified to species (ashy storm-petrel, Leach's storm-petrel, black storm-petrel) and banded with a unique, numbered, USGS hard-metal leg-band; often storm-petrel morphometrics were measured before birds were released. The types of morphometric data collected varied among research groups, but the most commonly and consistently collected morphometrics were bill length, skull length, tibiotarsus length, mass, and wing length, and presence/absence or description of an incubation patch. Prior to this data release, various datasets were housed by multiple organizations (e.g., USGS, CHIS, Point Blue Conservation Science) in various formats (e.g., reports, field notebooks, Excel spreadsheets, etc.). We archived, digitized, and compiled all available datasets from mist-netting efforts at CHIS to create a singular database of storm-petrel mist-netting data. The database consists of two tables: the 'CPUE' table contains the summary information for each mist-netting night and the 'captures' table contains the information for each individual captured. Several organizations have conducted mist-netting efforts at CHIS over the years, with variation in the net mesh size, net dimensions, audio file for vocalization playback, type of speaker system to broadcast vocalizations, parameters recorded, and data codes (e.g., both LESP and LHSP species codes were used to indicate Leach's storm-petrels). Therefore, we standardized data codes and noted any alternative codes used. We also identified missing pertinent information about each mist-netting night including start/stop times, species information, incomplete band numbers, decibel level of vocalization broadcast, participant names, net mesh size, and net dimensions. We filled data gaps to the extent possible by reviewing available reports, contacting participants, and cross-referencing with USGS Bird Banding Lab (BBL) records. Where inconsistencies persisted or when we could not standardize data, the record was flagged indicating that it should be removed from some types of analysis. We also improved database navigation by creating a unique catch identification code associated with each banding record and a unique netting night identification code associated with each mist-netting night. Depending on the protocol used, accessibility, and weather conditions at the site, mist-netting sessions occurred during one, two, or three sequential nights. We noted whether a netting night was the first (or only), second, or third night in a 5-day period so that the effect of sequential nights could be incorporated into analysis (Adams 2016). To standardize the number of ASSP captured across mist-netting efforts, we calculated catch-per-unit-effort (CPUE) as the number of ASSP captured per minute during 5.3 hours post-sunset in order to maintain a standardized cut-off period as timing of sunset varies through the netting season (Adams 2016). We calculated two metrics for CPUE: number of birds caught per minute during all hours of the night (raw CPUE), and number of birds caught per minute during the first 5.3 hours following sunset (standardized CPUE). Same night recaptures (e.g., individuals that were captured more than once within a mist-netting night) were noted, but excluded from CPUE. We also excluded unbanded individuals (n equals 20) from all analyses. These were individuals that were released, intentionally or not, without a band. We excluded these from the analysis because we cannot verify that these individuals were not captured more than one time within a mist-netting night (e.g., same night recaptures).

These data supports these recent publications:

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

Adams, J., Carter, H.R., McChesney, G.J. and Whitworth, D.L., 2016. Occurrence, morphometrics and plumage variability among Leach's Storm-Petrels Oceanodroma leucorhoa in the California Channel Islands, 1976-2015. Marine Ornithology, 44, pp.113-119.

Ainley, D.G., McIver, W. , Adams, J., and Parker, M., 2021. Ashy Storm-Petrel (Hydrobates homochroa). Birds of the World. Cornell Lab of Ornithology, version 1.1.