In the wild, chickens tend to sleep up high, similar to all other birds. This is a natural instinct due to their evolutionary traits and helps them feel safer and more secure. When they are perched, they can also detect potential threats more easily.
In addition, sleeping on the ground can be risky for them as they are more vulnerable to predators. If they are on the ground, they may get pecked to death by a hawk or other predator, or they might become too cold. They might also get contaminated by bacteria in poop or other mess. Lastly, chickens who sleep on the ground tend to soil themselves more frequently as they move around in search of clean surfaces.
They will often huddle together to conserve warmth when it’s cold as well. This is especially true for young chicks (under 5 weeks old) as they have underdeveloped feathers. They will usually hurdle up together, tuck their wings in and huddle close to each other for warmth.
Inside the coop, chickens are typically happiest when they can sleep on a roosting bar. This replicates the feeling they would have in the wild of sleeping on a tree branch and is important for their wellbeing as it gives them the chance to stay warm at night. Roosting bars also reflect the flock’s social structure and the hens higher up in the pecking order will have more desirable spots. This avoids fights and bullying, which can be stressful for the chooks and also cause them to lose out on much needed restful sleep.