How they see
How does an eagle see the world?
Violet vision at 2–3× your acuity
If you could borrow an eagle's eyes for a moment, the world would snap into almost telescopic focus. Soaring high above a field, it can pick out a rabbit or a blade-thin movement in the grass from a distance where we would see only an unbroken green carpet. Its colour vision is richer than ours too, with a fourth, violet-sensitive cone whose range reaches just into the near-ultraviolet.
See through their eyes
Human ≈ 60 cpd (20/10)
How sharp is an eagle's vision?
Its eyes resolve about 140 cycles per degree (20/4), while a human reaches around 60 cpd (20/10). Its field of view spans about 340°.
Colour comparison
How each colour shifts when seen through this animal's eyes, using the same colour model as the app. Tones a screen can't emit (such as ultraviolet) are shown as an approximation.
What colours can an eagle see?
Richer than human colour vision with an extra violet dimension; oil droplets sharpen colour discrimination.
Photoreceptors
Tetrachromat (4 cone types) + coloured oil droplets
Cone peak sensitivities
- V (violet)405 nm
- S (blue)450 nm
- M (green)505 nm
- L (red)565 nm
How does an eagle see in the dark?
Day-active; enormous eyes and a deep central fovea for magnification.
How does an eagle's vision compare to a human's?
An eagle sees roughly two to three times as sharply as you do, around 20/4 against your 20/20. On top of the three colours you already have, it adds a fourth, violet-sensitive cone that reaches just into the near-ultraviolet.
What is special about an eagle's vision?
- 2–3× human acuity
- Violet-sensitive, with colour-sharpening oil droplets
- Two foveas per eye
What the research shows
The famous acuity figure comes from Reymond (1985), who combined behavioural grating tests on wedge-tailed eagles with measurements of the eye's optics and anatomy. The behavioural limit came out near 140 cpd, about 2–2.3 times the human peak, and the anatomy fits: cone density near 450,000 per square millimetre, with spacing of around 1.6 µm, close to the limit set by diffraction. Red-tailed hawks come out at roughly twice human acuity. Each eye has two foveae, a deep central one used for distant sideways viewing and a shallow temporal one that serves the forward binocular field, where the two eyes overlap by about 20–40 degrees.
Colour vision rests on the avian photoreceptor work reviewed by Hart (2001) and on Lind, Mitkus, Olsson & Kelber (2013). Diurnal raptors are violet-sensitive rather than truly ultraviolet-sensitive: the shortest cone peaks around 405 nm and reaches only just into the near-ultraviolet, alongside cones near 450, 500–510 and 560–570 nm, each paired with a coloured oil droplet that sharpens its tuning. For the golden eagle, Doyle et al. (2014) confirmed from its SWS1 opsin gene that this cone is of the violet type. Flicker fusion of roughly 70–130 Hz is a raptor estimate; the page shows 120 Hz. A phone at arm's length displays only about 25–35 cpd, so the simulation can avoid blurring but cannot add detail, and a fourth colour dimension cannot be fitted onto three screen primaries.
Guides: Animals that see ultraviolet · Which animal has the best eyesight? · All guides
Scientific sources
- Hart (2001)
- Lind, Mitkus, Olsson & Kelber (2013)
- Reymond (1985)
- Doyle et al. (2014)
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