Sleep, sleep timing and chronotype in animal behaviour

In humans, sleep duration and sleep timing have been identified as interesting facets of individual differences and of personality. Sleep duration and sleep timing are different constructs. For example, compare two individuals both sleeping for 6 h: one may sleep from 2300 to 0500 hours and the other from 0100 to 0700 hours. One can assess the midpoint of sleep in these two subjects which is the midpoint in clock time between sleep onset and...