Figure 6. Variations in the cycling of daily egg temperatures of nine individual birds (3 from each species).

Each pane shows continuous logging of smoothed egg temperatures across multiple days. Sections of black line overlaid on the blue line denote night time periods based on ephemeris tables for the geographic coordinates of each colony (Table S1 in File S1). Temperature scales are consistent within each species but temporal periods varied slightly between individuals. However, all individuals shown were from equivalent calendar periods within a species to ensure similarity of environmental conditions that could potentially influence incubation behavior. Cycling coincides with a diurnal pattern and there is a distinct trend towards increased rhythmic temperature cycling with increasing egg size (i.e., species size). The pattern is less clear for the auklets but these birds nest in burrows or boxes and may be influenced less by diurnal patterns.