Unlike some hooved animals, deer don’t sleep standing (even in snow). And, when they lie down, it’s hard to tell whether they’re just resting or sleeping – they often sleep defensively, with their eyes open, their ears alert, and their noses inhaling local scents, according to the research.
When bedded, white-tails reportedly enter into a cycle of nodding off completely for a short time, then becoming searchingly alert for a similar time, and so on. Sleeping in groups increases the odds that at least one of them will be on the full alert segment of the cycle at most times. (Image taken in Brooklin, Maine, on January 30, 2023.) Click on the image to enlarge it.