LAUSR

STUDY OBJECTIVES To investigate sleep patterns in the camel by combining behavioural and polysomnography (PSG) methods. METHODS A noninvasive PSG study was conducted over four nights on four animals. Additionally, video recordings were used to monitor the sleep behaviours associated with different vigilance states. RESULTS During the night, short periods of sporadic sleep-like behaviour corresponding to a specific posture, sternal recumbency (SR) with the head lying down on the ground, were observed. The PSG results showed rapid shifts between five vigilance states, including wakefulness, drowsiness, REM sleep, NREM sleep, and rumination. The camels typically slept only 1.7 hours per night, subdivided into 0.5 hours of REM sleep and 1.2 hours of NREM sleep. Camels spent most of the night either awake (2.3 hours), ruminating (2.4 hours) or drowsing (1.9 hours). Various combinations of transitions between the different vigilance states were observed, with a notable transition into REM sleep directly from drowsiness (9%) or wakefulness (4%). Behavioural postures were found to correlate with PSG vigilance states, thereby allowing a reliable prediction of the sleep stage based on SR and the head position (erected, motionless or lying down on the ground). Notably, 100% of REM sleep occurred during the head lying down-SR posture. CONCLUSIONS The camel is a diurnal species with a polyphasic sleep pattern at night. The best correlation between PSG and ethogram data indicates that sleep duration can be predicted by the behavioural method, provided that drowsiness is considered a part of sleep.