Data from: Sex-specific, inverted rhythms of breeding-site attendance in an Arctic seabird

In contrast to the widespread presence of daily rhythms in the presence of the geophysical light-dark cycle, organisms at polar latitudes exhibit diverse diel activity patterns during natural periods of continuous solar light or darkness (polar day and night, respectively), from 24-h rhythms to arrhythmicity. In Arctic Greenland (73.7°N, 56.6°W) during polar day, we observed breeding-site attendance rhythms of thick-billed murres (Uria lomvia; n = 21 pairs), a charadriiform seabird, which provide biparental care at the colony. We found that U. lomvia egg-incubation and chick-brooding attendance is rhythmic and synchronized to the geophysical day (mean period length [rhythm duration] ± 95% CI = 24.13 ± 0.52-h). Individual pair members had temporally segregated, sex-specific colony-attendance rhythms that were opposite (inverted) to each other and these sex-specific rhythms were prominent at the population level. Our results provide a basis for investigating circadian systems at polar latitudes and sex-specific parental-care strategies.