Birds can see in the dark and some birds such as owls have exceptional night vision and can see better than other birds in the dark.
Birds such as diurnal birds can somewhat see in the dark but not as good as owls.
Owls have tube shaped eyes which provide the owl with binocular vision and depth perception which helps them hunt in the dark.
Birds also have more rods than cones in their eyes and the rods are more sensitive to low light, which helps the bird see in the dark.
Birds don't fly at night because most birds are diurnal, which means the birds are active during the day and sleep at night.
Birds eyes are not suited well for nighttime and birds also need to sleep and recover from the daytime activities.
Birds don't fall out of trees when they sleep because birds have several adaptations and ways that help the bird stay upright and avoid falling out of trees during sleep.
Common adaptations and ways birds avoid falling out of trees include.
Limited rapid eye movement sleep.
Birds can restrict REM sleep to only part of the birds brain at a time, which helps the bird remain in an upright position.
Birds also have an extra balance sensing organ between their hips which helps the bird stay upright.
And birds also have feet that automatically lock.
Once a bird lands on a branch the muscles in the birds leg automatically tighten, which forces the birds tendons in their feet to contract.
As a result it causes the birds toes to pull inward and creates a tight grip around the branch so the bird doesn't fall.
Some birds do sleep by laying down in their nest and other birds sleep standing, perched, tucked under a wing, floating or even upside down.
Birds can stand on one leg while they sleep, can perch on a branch or windowsill and even tuck their head under a wing while sleeping.
Some birds such as ducks can sleep while they float on water and some birds can sleep upside down.
While birds do sometimes sleep laying down it's not the same way as humans lay down to sleep.
Some birds sleep with their eyes closed and some birds sleep with one of their eyes open.
The bird that can sleep with one eye open are Mallard birds.
Mallard birds are birds that sleep in groups and often sleep with one eye open if they're on the outside of the group.
The open eye of the Mallard bird is directed away from the other birds.
Other birds that can sleep with one eye open are Geese, chickens and Oystercatchers.
Oystercatcher birds have an eye blinking strategy that is called "peeking" which allows the bird to sleep while also periodically opening one of their eyes to monitor their surroundings.
Chickens also often sleep with one eye open.
Oystercatcher birds are a group of waders that form the family Haematopodidae, which have a single genus, Haematopus.
Oystercatcher birds are found on coasts worldwide apart from the polar regions and some tropical regions of Africa and South East Asia.
The oystercatcher bird is a boldly patterned shorebird that has red-yellow eyes and a vivid red-orange bill, American Oystercatchers survive almost exclusively on shellfish—clams, oysters, and other saltwater molluscs.
Because of the oystercatchers specialized diet, oystercatchers live only in a narrow ecological zone of saltmarshes and barrier beaches.