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What animal has red eyes at night?

Many nocturnal animals have eyes that appear red or orange when illuminated in the dark. This is due to a reflective layer in their eyes called the tapetum lucidum which allows more light to pass through the retina, improving night vision. Some common animals with eyes that glow red at night include cats, dogs, raccoons, opossums, deer, horses, cattle, rodents, rabbits, reptiles, amphibians, fish, spiders, and even some birds.

Animals with Tapetum Lucidum

The tapetum lucidum is a specialized structure in the eyes of many vertebrates that lies behind the retina and reflects visible light back through the retina, increasing the light available to the photoreceptors. This allows animals to see better in low light conditions. When a bright light shines on the eyes of an animal with an intact tapetum lucidum, the eyes will glow red or orange.

Animal Tapetum Lucidum?
Cats Yes
Dogs Yes
Raccoons Yes
Opossums Yes
Deer Yes
Horses Yes
Cattle Yes
Rodents Most species
Rabbits Yes
Reptiles Some species
Amphibians Some species
Fish Some species
Spiders Yes
Birds Some species

As shown in the table, many common mammals, along with some fish, reptiles, amphibians, arachnids and even birds, possess a tapetum lucidum structure that causes their eyes to glow red or orange in the dark when illuminated.

Advantages of the Tapetum Lucidum

The tapetum lucidum provides several advantages for animals that are active in low light conditions:

  • Enhances night vision by reflecting light back through the retina, allowing photoreceptors a second chance to absorb photons.
  • Increases visual sensitivity up to 1000 times in dim light.
  • Enables animals to see with less than 1% of the light needed by humans.
  • Allows animals to detect motion and faint outlines in very low light.
  • Gives animals improved night hunting abilities.

The enhanced night vision provided by the tapetum lucidum gives animals better nocturnal predation success and helps them avoid becoming prey. It also aids navigation and spatial orientation in dim conditions.

Mechanism Behind Glowing Eyes

When bright light enters the eye and passes through the retina, most of it is absorbed. Any remaining light is reflected off the tapetum lucidum at the back of the eye, passing once more through the retinal photoreceptors. This “double passage” of light allows the photoreceptors a second chance to absorb photons and send stronger visual signals to the brain.

However, if the incoming light is very bright, such as from a flashlight or camera flash, the tapetum lucidum reflects the excess light back out through the retina. This reflected light exits the pupil, causing the eyes to glow. The specific color depends on the angle of reflection and wavelength of the reflected light.

Colors Explained

While glowing eyes may look red, orange, yellow, green, blue or violet, the tapetum lucidum itself does not contain pigments or colored cells. The observed color is due to the wavelengths of light being reflected back out of the eye.

Perceived Color Explanation
Red Longer wavelengths around 640 nm
Orange Medium wavelengths around 600 nm
Yellow Medium wavelengths around 580 nm
Green Shorter wavelengths around 530 nm
Blue Very short wavelengths around 450 nm
Violet Extremely short wavelengths around 400 nm

As shown in the table above, longer wavelengths in the red end of the visible spectrum are reflected when the light enters the eye straight on. Shorter wavelengths like blue and violet are reflected when the light beam hits the tapetum lucidum at an oblique angle.

Differences Between Species

While any animal with a tapetum lucidum will show eyeshine at night, there are some differences between species:

  • Cats and dogs: Glowing eyes are easiest to see in cats, dogs, and other carnivores. Their retinas are rod-dominated to enhance night vision, and the tapetum lucidum is very reflective.
  • Herbivores: Animals like cattle and horses have less reflective tapetums, as they are active both day and night. Their eyes glow less brightly.
  • Rodents: Rats, mice, hamsters, etc. normally have a less organized tapetum that produces diffuse eyeshine rather than bright pinpoints of light.
  • Birds: Only some birds have a tapetum lucidum, like owls and nightjars. Diurnal birds lack it, so their eyes do not glow.
  • Reptiles: Snakes, geckos, crocodiles, and some lizards have a tapetum lucidum that creates bright eyeshine.
  • Spiders: Most spiders have reflective eyes due to mirrored surfaces rather than a tapetum lucidum.

So in summary, the characteristic bright red eyeshine is most pronounced in predatory mammals like felines, canines and raccoons that rely strongly on night vision and have highly organized, reflective tapetums.

Other Causes of Glowing Eyes

While the tapetum lucidum is the primary cause of eyeshine in the dark, there are some other rare causes of glowing eyes in animals at night:

  • Bioluminescence: Some deep sea fish generate their own light through bioluminescent organs around their eyes.
  • Polarized lenses: The oriented lenses in some invertebrates can reflect light back in specific directions.
  • Iridophores: Reflective cells in amphibian and fish skin can create eyeshine.
  • Eye disease: Certain eye infections or cancers can sometimes cause a glowing appearance in animals.

However, these other causes are quite uncommon compared to the widespread occurrence of the tapetum lucidum in vertebrates adapted for nocturnal vision.

Conclusion

In summary, many nocturnal and crepuscular animals have glowing red or orange eyes when illuminated in the dark due to the presence of a reflective tissue called the tapetum lucidum. This specialized structure enhances night vision by reflecting light back through the retina for a second pass through the photoreceptors. The particular color observed depends on the angle and wavelengths of reflected light. Glowing eyes are most noticeable and colorful in predatory mammals like cats and dogs. So next time you see a pair of shining eyes in the night, it likely belongs to an animal making use of its amazing low-light adaptations to hunt and navigate in the darkness!