To fly high in the sky, a bird must have impeccable eyesight. Vision is the most important sense for birds as they need to spot good landing places, even in dense woodland or thick hedgerows.
Most species of birds can usually see 2-3 times better than humans. Birds of prey can see up to 8 times as well and can spot prey from over 2 miles away. Birds can see ultraviolet light which helps them detect food and stay away from predators.
While every bird species is different, good eyesight is commonly shared. How well do birds see? Let’s find out.
Birds are animals but some people don’t realise why. Find out more here
Bird Vision
Most birds have large eyes compared to the relative size of their head, giving them a good advantage when it comes to watching for predators and foraging for food. Many species also rely on bright coloured plumage as part of their courtship displays, so sharp vision is essential.
When it comes to seeing objects in sharp focus, most bird species can see 2-3 times farther away than the average human.
A bird’s colour vision is just as strong as its clarity of vision. Humans have three types of photoreceptor cells, which are sensitive to a particular colour; red, green or blue. Birds have four types of photoreceptor cells. This allows them to see UV light as well as the primary colours.
The addition of this fourth type of photoreceptor cells allows birds to see colours that humans have never seen and do not have names for. We may never know what birds see with their additional photoreceptor cells, but it may be one of the reasons that birds have such distinctively bright colours to their plumage.
Birds sensitivity to light is also far superior to humans. This improves their vision at dawn and dusk when many other animals struggle to see due to low light.
The ability to see ultraviolet light may help birds on several levels. Firstly, birds see UV light differently from us. While we see a single solid beam of light, birds see UV light as short pulses. Experts believe this enables birds to use the stars to navigate at night, especially species that migrate long distances.
In addition, certain fruits and berries emit ultraviolet light, which makes them much easier for birds to see while they are foraging.
Like dolphins and some whales, birds can sleep with one eye open. This creates an environment where a bird can rest one half of its brain and avoid sudden danger. During sleep, birds close their eyes one of two ways. Owls close their eyes by moving the top eyelid down over their eye. Most other birds are the opposite, moving the lower lid up.
Birds also have a nictitating membrane, often referred to as a third eyelid. The membrane is a thin flap of skin of a translucent, off white colour. Unlike normal eyelids, nictitating membranes move sideways across the eye instead of up and down. The role of this membrane is to keep the eye moist and protect it from debris.
Find out more about colour vision in birds in this article I wrote
How Far Can A Bird See?
Most bird species have excellent eyesight, but birds of prey have remarkable long-distance vision. Some bird species can see 7-8 times as far as a human, with the ability to spot a prey animal from up to 2 miles away.
While each bird species has good vision, their field of view is different. Ducks and geese have their eye positioned relatively high on the side of the head and see with monocular vision. This means they can use each eye separately. Their vision is best when looking to the side and is limited when looking at objects ahead of them.
Birds also have the advantage of moving their heads in different directions at rapid speed. This increases their field of view momentarily and allows them to see much more of their surroundings.
Which Bird Species Has The Best Eyesight?
Birds of prey have the best eyesight of any avian group. Their large, forward-facing eyes allow them to see in fine detail for miles, and they can pinpoint a rabbit from more than 1 mile away. Birds of prey have binocular vision, meaning both eyes are used together to view the same thing.
In proportion to their body size, some species of eagle have eyes one and a half times larger than an average size bird. The wedge-tailed eagle has the clearest vision of any animal on the planet and the largest eye to body size ratio of any bird species. Bald eagles have the longest distance vision of any bird species.
Kestrels can hunt voles and other small rodents by following the UV glow from their prey’s urine. This gives them a significant advantage as they hover at high altitudes where bright light might otherwise be a hindrance.
Owls eyes are so large that you can see the back of their eyes when looking through their earholes! As nocturnal animals, owls rely on their excellent eyesight to hunt fast-moving rodents at night and avoid obstacles during fast flights.
Which Bird Species Has The Worst Eyesight?
While all birds have clear eyesight, not all are equal. Kiwis, the national animal of New Zealand, have tiny eyes and the weakest eyesight of any bird species.
To compensate for their poor vision, they have an exceptionally well-developed sense of smell, which helps them forage for food and sense nearby predators.
Interestingly, while birds generally have fantastic eyesight, they do not learn visual markers as humans do. This makes glass indistinguishable for birds, explaining why it is so common for birds to fly into windows and glass doors.
Do you know how kestrels hunt? Find out in this article I wrote
