Deployment and recovery of geolocator devices
Geolocators (seven BAS Mk18-L, and one Mk14) were deployed on both legs of four adult puffins during the 2010 summer breeding season on Skomer Island, Wales (51.737N, 5.297W). Single geolocators (31 Biotrack (2012)/Lotek (2020) Mk4083 and 12 BAS Mk18 (2010)) were deployed on 40 adult puffins during the breeding season in 2010, 2012 and 2020 on Skellig Michael, Ireland (51.771N, 10.539W). Birds at both colonies were captured during chick-rearing either using purse nets at burrow entrances or by hand from the burrow, weighed and fitted with geolocators before being released back to their burrow. Capture and handling times were kept to a minimum. Geolocators were attached to a coloured plastic ring fitted around the tarsus, with total deployment weight (devices plus leg ring and cable tie attachment) always < 2% body mass, under 6g for dual-equipped loggers, and under 3g for single-equipped loggers. These devices measured light every minute in 6-bit units from 0 (light is below civil twilight, sun > ~ 6 degrees below the horizon) to 64 (sun is well above the horizon) and saved the maximum light level sampled in 5-minute intervals, or 10-minute intervals for the single Mk14 logger used. Saltwater immersion data were sampled every 3 seconds as binary units of 0 (dry) or 1 (wet) and the number of wet samples in 10-minute intervals were saved as values between 0 (all dry) or 200 (all wet). Devices were recovered from birds during the subsequent breeding seasons. All work was carried out under licence from the British Trust for Ornithology (CO/6143, C/5311), with work in Ireland further licenced by the National Parks and Wildlife Service (06/2020, C41/2020, 26/2010, C051/2011, C116/2012, C039/2013, 11/2013). Attachment of dual-equipped geolocators was granted ethical approval by the British Trust for Ornithology Unconventional Methods Technical Panel, with ethical approval for handling and tagging in Ireland also approved by the University College Cork Animal Ethics Committee. All analyses were performed using R version 4.1.2 (R Core Team, 2021), and all code to run these analyses are available online (github.com/JamieHDarby/puffin_moult).