Sleep with Open Eyes in Two Species of Deer, the Indian Sambar (Rusa unicolor) and Sika Deer (Cervus nippon)

• Published in: Doklady. Biological sciences Vol. 512; no. 1; pp. 295 - 299
• Main Authors: Lyamin, O. I., Siegel, J. M., Nazarenko, E. A., Vu, Manh, Rozhnov, V. V.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01.10.2023; Springer Nature B.V
• Subjects: Animals; Biomedical and Life Sciences; Cervus nippon; Croup; Deer; Evolutionary Biology; Life Sciences; Plant Sciences; Posture; REM sleep; Rusa unicolor; Sleep; Ungulates; Vigilance; sleep; slow wave sleep; rest; vigilance; ungulates; Indian sambar; Cervidae; sika deer; REM sleep; Rusa unicolor; Cervus nippon
• ISSN: 0012-4966; 1608-3105
• DOI: 10.1134/S0012496623700679

The relationship between postures, sleep stages and eye state was established in two species of deer, the Indian sambar ( Rusa unicolor ) and sika deer ( Cervus nippon ), based on video recording. In both species, the state of rest or behavioral sleep was recorded in the sternal position, holding the head above the ground, and in the lateral position, with the head resting on the croup or on the ground. Rest accounted for at least 80% of the time in these positions. Based on behavior criteria a substantial portion of rest represented slow-wave sleep. Episodes of rapid eye movements (REM sleep) were recorded in the lateral position. They did not exceed 2 min. When the deer were in the sternal posture, they kept their eyes open most of the time: in average 96% of the time in sambars and 82% in sika deer. Episodes of the open eye in this posture lasted up to 8.4 min in sambars and up to 3.3 min in sika deer. In the lateral position, such episodes were 4 and 1.5 times shorter. Sleeping with open eyes in ungulates may be an important mechanism of maintaining vigilance.