Testing single leg data in dual-equipped birds
A similar moult identification method was attempted using data from each dual-equipped logger in isolation. As before, the proportion of time spent wet was corrected for tucking behaviour using raw light signals. Any points with a solar angle below -3 degrees were omitted for this analysis, to ensure that leg-tucking was sufficiently captured using light data. Propflight and propflight-5were again calculated, and the same incrementing threshold method was used to identify putative moult periods of minimum 30 days duration. A maximum threshold value of 1% propflight-5 was applied to restrict the likelihood of falsely identifying moult from noisy immersion time series. This meant that the 5-day rolling average of corrected flight, or propflight-5, had to remain below 1% for a period to be considered as moult. Independently derived inferred moult periods were compared to combined data from dual-equipped loggers. Based on limited but good agreement (see results), the process was then applied to the geolocator data collected from 40 individuals equipped with single loggers from Skellig Michael, Ireland.
Observations from captive puffins
Several aquaria house captive puffins as part of displays. Aquarists from 3 of these facilities provided observations about moulting habits of their captive puffins to contextualise our results and test whether our conclusions were physiologically viable. We spoke to aquarists from Tierpark Bern, Switzerland, the National Aquarium, USA, and Oceanário de Lisboa, Portugal. All described variation in moulting behaviour, see details in supporting information. Further relevant observations are referenced as personal communications in the main text.