How do owls see at night?

Most owls are nocturnal, meaning they are active at night or during the twilight periods of dusk and dawn. As birds of prey, owls need to be able to see well in the dark so they can hunt small animals such as mice, voles, and other rodents, which are also active at night. Owls’ eyes have evolved many special characteristics to boost their night vision. Owls have very large eyes to help catch a lot of light. The retina is the part of the eye that receives images and sends them to the brain, and it has two types of light-sensitive cells: rods, which detect light and movement, and cones, which detect colour. Owl eyes are packed with rods, about 30 for every cone (humans have about 20 rods for every one cone), making them very good at noticing movement in the dark. 

Other eye-opening facts: Owl eyes are fixed in place in their heads; they cannot move their eyes around in their sockets like humans can. That’s why owls evolved the ability to move their whole head almost all the way around (up to 270 degrees, three-quarters of a full circle) to look in different directions. Owls can see during the day too, but since their large eyes catch so much light, they often close their eyes halfway in daylight to block some of the incoming light. 

This article originally ran in Nature Alberta Magazine – Summer 2023.