Figure 1.

Activity profiles of red-backed shrikes (Lanius collurio) in the wild and in captivity. Left: movement and nocturnal migratory flight of a single, free-flying Danish shrike monitored from July 2014 until July 2015 by Bäckman et al. [20]. Right: comparison of nocturnal activity of the same free-flying shrike (top) with mean activity of 10 hand-raised conspecifics recorded in captivity (bottom) [21]. Shrikes originated from Gribskov, Denmark (top, 56°N) and Lemsjoeholm, South Finland (bottom, 60°N), respectively. On the left, each horizontal line represents accelerometer data from 2 consecutive days, where the second day is repeated as the first day on the next line. Colours encode mean activity level for each hour ranging from no activity (white) to continuous flight (black) with intermediary levels in colour. On the right, data are approximately monthly average numbers ±s.e. of half-hour periods between 18.00 and 06.00 h when birds were active during dark hours, plotted against time of year. Captive birds were kept under constant photoperiodic conditions (LD 12 : 12 h) [21]. For captive birds, vertical shadings indicate the timing of prenuptial (prealternate) moult (light grey: body moult, embedded in it, in dark grey: wing moult).