Warning: SPOILERS for The Walking Dead season 11, episode 1, "Acheron: Part I."
The Walking Dead season 11 premiere featured a new behavioral trait of walkers, suggesting the franchise's zombies have the ability to sleep. The episode titled "Acheron: Part I" kicked off the eleventh and final season of The Walking Dead, which will run for a total of 24 episodes. Following the six bonus episodes that brought season 10 to a close, the final season picked up with Alexandria's desperation considering the community's depleted supplies, particularly with food.
In the nearly silent opening sequence at the start of The Walking Dead season 11, core members of the group infiltrated a military base from the roof. The mission, led by Daryl, Carol, and Maggie, almost went off without a hitch. The women of the group, including Rosita, Magna, Lydia, and Kelly, joined Maggie and Carol by dropping into the base as a sea of walkers layered the floor below. Instead of roaming, the walkers dressed in military uniforms were seemingly asleep, forcing the group to remain as quiet as possible. The group then found the base's supply of MREs or "Meals Ready-to-Eat," which they packed to send to the rest of the group on the roof. Of course, the plan went sideways when a few drops of blood from Daryl's injury from the rooftop dropped on one of the sleeping walkers, waking it up before the horde followed suit.
While The Walking Dead has previously shown zombies in a weakened state, the season 11 premiere was the first time to reveal that the undead has the ability to sleep. The military sequence even included dialogue in which the group warned not to wake up the walkers, suggesting the characters are aware of this napping habit. The fact that Walking Dead zombies are now sleeping could play into the current theme of dwindling supplies. Though the worry had been focused on humans not being able to find food for survival, it's likely walkers are experiencing a common problem.
The Alexandria group likely dropped into the base from the roof with ropes for a quiet entry. Then again, it's possible there was no other suitable way in considering it looked to be an underground location. With that said, the dead military personnel seen sleeping on the ground were likely trapped once they all turned into walkers. Clearly, MREs wouldn't have satisfied them as they would need human flesh to relieve their hunger. Without humans around, they could have grown weaker and weaker before electing to sleep with no other purpose.
The fact that zombies can sleep either from a lack of food or because of boredom presents a new twist in The Walking Dead TV lore. Their behavior aligns with the theory that existing zombies will eventually waste away without a food source. With the human population diminished, especially considering the time that has passed since the start of The Walking Dead, walkers don't have a food supply as they did in the early days of the apocalypse. Perhaps the changes in the food supply have altered their behavior and zombie evolution, or in this case, devolution.