Conclusion
While limited to a small sample size, the results of this study markedly advance our understanding of a vulnerable period in the non-breeding season of a threatened species. We raise the intriguing possibility that puffins have a unique biannual flightless moult, leaving them flightless for 60-80 days over the course of a single non-breeding season, accounting for 20-30% of that total period. This highly unusual strategy may be tied to migration effort, though this is speculative due to our limited sample size. However, we have established a freely available workflow to further analyse dual-equipped seabirds to improve behaviour classification using geolocators. We hope this will promote further research on the flightless moult of puffins and other alcids, given that this life stage that leaves them are particularly vulnerable to antagonistic impacts from reduced prey availability, surface pollution and increased storm prevalence.