Annual cycle based on the eight monitored Long-tailed Skuas (median values followed by ranges in brackets).

aThis represents the latest estimated start of migration for individuals. First geolocated positions were obtained when the birds were south of the constant daylight zone. We assumed that the birds started the migration one day before the first position was geolocated.bAssuming direct flight along black lines as in Figure 1, from last geolocated position to the colony with the same speed as that of the average over the previous 10 days.cNest initiation dates were estimated by means of egg floatation [62].