Figure 5.

Daily patterns of activity of individual #4 between Nov 15, 2012 and Nov 15, 2013 as a representative example. Leftmost panel: Actogram of activity showing black bars for each 3 minute interval, with a height proportional to activity, one horizontal line for each day. Yellow lines indicate beginning and end of civil twilight (i.e. the geometric centre of the Sun’s disk is ≤6° below the horizon), a luminance that is sufficient to cause photic responses, e.g., suppression of melatonin production⁴⁵. Second panel: Normalized power of rhythms with period lengths between 30 minutes and 30 hours identified by Lomb-Scargle periodogram analysis. Horizontal red lines indicate the significance threshold of p = 0.001. Lines and arrows to the left indicate the intervals analysed, i.e. the period when the sun is continuously below the horizon during winter (Polar Night, DD), the periods with daylight and night (LD), the period of continual light (Midnight Sun, LL) before the onset of the vegetation period with NDVI values <0 (LL low), and the period of continual light with above-ground live vascular plants (NDVI >0, LL high). Third panel: as second panel but with periodograms of 15-day intervals. Rightmost panel: 16-day mean NDVI values from the three major parts of the study site for 2013 (see Fig. 1) and a baseline cosine fit to this data.