Figure 5: Timing and location of inferred moult of Skellig Michael puffins. On the left, the proportion of time spent dry per day is graphed over the non-breeding season. The green line represents time spent dry per day (propflight) and the blue line is the 5-day rolling average of this (propflight-5). The blue bar underneath each plot represents putative moult inferred by the moult identifiation process. On the right, the corresponding inferred moult location is shown by a diamond shape, overlaid on the migratory path of the individual. The red dot represents Skellig Michael, their breeding colony. Note that portions of the track apparently crossing land are products of the inaccuracy of geolocator location estimates around the equinoxes, and associated smoothing.
Of the 40 single-equipped individuals from Skellig Michael, inferred moult periods were only apparent in 3 individuals. Periods of sufficiently reduced flight consistent with moult were not detected by our method in any of the other individuals (supporting information). These moult periods were 35, 52 and 72 days in duration and occurred in midwinter, starting in December or January, and took place either beyond the Irish Atlantic shelf margin (n = 2) or in the Mediterranean Sea (n = 1) (figure 5 & supporting information). Puffins from Skellig Michael showed reduced leg-tucking activity around midwinter, especially for puffins tagged in 2020, which corresponds with the moult periods inferred for this group (supporting information). This suggests that moult is more easily identifiable at this time of year due to an apparent reduction in leg-tucking behaviour, so the temporal distribution of moult inferred here is likely biased towards this period. These 3 individuals all moved approximately 2000 km from the colony to their furthest point of residency (supporting information), comparable to one of the Skomer birds that was inferred to have completed two moults.