This figure is a plot of blackcap body temperature against time of day between 16.00 (4 p.m.) and 08.00 (8 a.m.) the next day. The hours of darkness are from about 7 p.m. until 6 a.m. The vertical (body temperature) axis is marked from 37 to 43 °C. From 4 p.m. until about 7 p.m. body temperature fluctuated between 41 and 42 °C, after which it fell steeply to 38.5 °C just before 9 p.m. Temperature then rose steeply back up to 41-42 °C, but fell sharply again about an hour later. The brief period (about 90 minutes) of relatively high nocturnal body temperature is shown as a grey bar. By shortly after midnight, body temperature had fallen to 37.4 °C, which is the lower limit of normal resting body temperature (shown as a horizontal dashed line). There were some fluctuations in body temperature over the next 5 hours, with values never exceeding 40 °C and at 2.30 a.m. a temperature as low 36.5 °C was recorded. At about 5.30 a.m. there began a sustained rise in body temperature, bringing it back up into the 41-42 °C range by 7 a.m.