Behavioral sleep in the Asian elephant in captivity.

Sleeping behavior was investigated during 294 nights for female Asian elephants (circus: n = 7; zoo: n = 5; including an infant). The animals were recorded continuously on time-lapse video tapes for 7-16 days consecutively. Seasonal changes in sleep behavior were studied by comparing summer (16-day) and winter (13-15-day) recordings; and sleep development was assessed by recording a mother and her infant for three consecutive nights per month for 15 months (age 5-19 months). Sleep occurred in a recumbent (RS) and in a standing position (standing sleep: SS). Although signs of paradoxical sleep (PS) were often evident, the exact onset and end of a PS episode could not be determined. Sleep onset occurred after 2100 hours, and sleep increased progressively reaching a maximum between 0100 and 0400 hours. Total sleep time (TST) in the adults comprised 4.0-6.5 hours per night (including 13.8-130.9 minutes of SS) and did not differ between the two groups. Seasonal differences were present in TST and in the distribution of sleep within the night; more sleep occurred in the winter. The duration of RS episodes in the adults was 72.0 minutes, a value far below the sleep-cycle length of 124 minutes that others have reported for elephants. TST in the infant decreased during the course of the 15-month recording period from 8.1 hours to 5.1 hours. SS occurred for the first time at the age of 9 months.