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.