Many people choose to cover their bird’s cage at night. While it’s not necessary, there are a few possible benefits. First, it means your bird is less likely to wake up at the crack of dawn and wake up everybody else in the house. Birds are very light-responsive: they sleep when it’s dark and wake up when there’s light. If you cover their cage, it gives you more control over this. It also allows the birds to sleep in a little bit — many of them probably aren’t going to bed when the sun sets, since they live in a house with electricity!
Covering the cage can also help reduce "night frights.” Night frights are when something scares the bird at night and they end up flapping all over the cage in the dark, potentially hurting themselves. Some birds, like cockatiels, are particularly prone to this. Pet birds cannot see well in the dark, so things like the moving shadows in a dark room can really scare them. Usually you won’t even know what it was that scared them. If you cover them, that eliminates most of those sorts of visual stimuli.
You might consider placing a small nightlight near your bird’s cage. If your bird does have a night fright, she can use that light to see her back to her sleeping perch.
Sleep is a good way to monitor your bird’s health. If she is sleeping on the floor of the cage, that’s frequently a sign of poor health. Birds, being prey animals, are very good at hiding their symptoms. By the time they’re willing to sleep exposed on the ground, they are often feeling very bad indeed. A bird on the floor may be a female about to lay an egg, but if it is, that should become apparent fairly quickly. If your bird is sleeping on the floor for long periods of time, it’s time to get them to the veterinarian.
It’s not at all uncommon for birds to nap throughout the day at different spots in the cage or on their owners. As long as your bird has active periods and seems alert and responsive when they are awake, she is most likely just fine.
Many birds will do a thing called "beak grinding” as they settle down to sleep. This is where they rub the two mandibles of their beak together, producing a soft sound almost like teeth grinding. New owners are sometimes concerned by this, but this is actually a good sign. Birds do this when they are very content and relaxed, which is why they tend to do it right before dozing off. Hearing my cockatiels beak-grind on my shoulder is one of my favorite sounds in the world, because I know it means they are very happy to be with me.
Want to know more about birds and sleep?
The Science of Bird Sleep
Parrots Need Sleep