Time course of each vigilance state, wake (red), sleep (purple) and drowsiness (purple), in each of the four seasons. Values plotted as mean number of minutes (± SEM,) of each state in 1-hour intervals. Time 0 represents lights on. Note that the fall birds were not scored on the same day and so each bar indicates the dark period for one of the three birds.
Jones et al. BMC Neuroscience 2010 11:87 doi:10.1186/1471-2202-11-87