How animals see in the dark.....

Some animals see differently than we do. Some animals, like bees, have cones for colors we can't see. Some animals have developed a highly-advanced senses of smell or specialized hearing abilities such as echolocation. Others have acquired eye adaptations for improved night vision

Big Eyes

The most interesting feature of nocturnal animals is the size of their eyes. Large eyes, with a wider pupil, larger lens and increased retinal surface collect more light. Some animal species have evolved tubular eyes as a means of increasing their size. Many nocturnal animals cannot move their eyes within the orbit. Instead, they have evolved extraordinary rotational ability in the neck. Owls, for example, can rotate their neck through 270° & this aids their vision.

Some animals of the night have acquired a spherical lens and widened cornea to compensate for reduced eye movement. This combined with a wide cornea increases the animals field of view allowing the head and eyes to remain motionless.

Mirrors Add Intensity, Eyes glow in the dark

On a dark night, flash a bright light at your dog or cat's eyes & you notice that their eyes glow in the dark. It is the tapetum lucidum (meaning "bright carpet"), an adaptation for night vision. The tapetum is a thick reflective membrane, 15 cells wide, directly beneath the retina.  It collects and re-emits light back to the retina a second time, giving the rods a second chance to absorb the image information, thus maximizing the little light available to them. As this light is reflected off the tapetum, the animal's eyes appear to glow.

Although nocturnal animals see mostly crude or imperfect shapes, outlines and no colors, by maximizing their sensitivity to low light levels with the above adaptations, it is enough for them to hunt, feed and survive in the dark of night.
 

In The Daylight

Most nocturnal animals are often  inactive during the day to avoid over-stimulating their highly sensitive eyes. Nocturnal animals have specialized pupils to shut out damaging bright day light. Nocturnal animals dilate their pupils to their circular maximum at night.

Amazing Animal Senses

Animals have developed amazing adaptations to their environments. Many different types of energy & senses exist in the environment, some of which humans cannot detect. Here are some examples of how some animals sense the outside world.

Ants

• Can detect small movement through 5 cm of earth.
• Can see polarized light.

 Bats

• Can detect warmth of an animal from about 16 cm away using its "nose-leaf".
• Bats can also find food up to 18 ft. away and get information about the type of insect using their sense of echolocation.

 Bees

• Can see light between wavelengths 300 nm & 650 nm.
• Have taste receptors on their jaws, forelimbs and antennae.
• Worker honey bees have a ring of iron oxide in their abdomens that may be used to detect magnetic fields. They may use this ability to detect changes in the earth's magnetic field and use it for navigation.
• Can see polarized light.

 Butterfly
 

• Has taste receptors on its feet.
• The butterfly has hairs on its wings to detect changes in air pressure.
• Using vision, the butterfly Colias can distinguish two points separated by as little as 30 microns.

 Cat

• Has hearing range between 100 and 60,000 Hz.
• Olfactory membrane about 14 sq. cm.  For comparison, humans have an olfactory membrane of about 4 sq. cm.

 Chameleon
 

• The eyes of the chameleon can move independently & can see in two different directions at the same time.

 Cockroach

• Can detect movement as small as 2,000 times the diameter of a hydrogen atom.

 Crab

• Has hairs on claws and other parts of the body to detect water current and vibration.
• Many crabs have their eyes on the end of stalks.

 Cricket

• Can hear using their legs; sound waves vibrate a thin membrane on the cricket's front legs.

 Dog
 

• Has olfactory membrane up to 150 sq. cm.
• Can hear sound as high as 40,000 Hz.

 Dolphin

• Like bats, dolphins use echolocation for movement and locating objects.
• Can hear frequencies up to at least 100,000 Hz.

 Dragonfly

• Eye contains 30,000 lenses.

 Earthworm
 

• Entire body covered with chemoreceptors ( taste receptors ).

 Elephant

• Has hearing range between 1 and 20,000 Hz. The very low frequency sounds are in the "infrasound" range.  Humans cannot hear sounds in the infrasound range.

 Falcon
 

• Can see a 10 cm. object from a distance of 1.5 km.

 Fish

• Have a "lateral line" system consisting of sense organs ("neuromasts") in canals along the head and trunk. These receptors are used to detect changes in water pressure and may be used to locate prey and aid movement.
• Some fish can see into the infrared wavelength of the electromagnetic spectrum.

 Fish ( Deep sea  )
 

• Only have rods in the retina: 25 million rods/sq. mm. Perhaps they need this high density of photoreceptors to detect the dim biolumninescence that exists in the ocean depths.

 Fish ("Four-eyed Fish" Anableps microlepis)

• Can see in air and water simultaneously. Each eye is divided by flaps, so there is one opening in the air and one in the water.

 Fly

• Eye has a flicker fusion rate of 300/sec. Humans have a flicker fusion rate of only 60/sec in bright light and 24/sec in dim light. The flicker fusion rate is the frequency with which the "flicker" of an image cannot be distinguished as an individual event. Like the frame of a movie...if you slowed it down, you would see individual frames. Speed it up and you see a constantly moving image.
• Blowflies taste with 3,000 sensory hairs on their feet.

 Frog

• Has an eardrum (tympanic membrane) on the outside of the body behind the eye.

 Hawk
 

• Normal vision for people is 20/20. A hawk's vision is equivalent to 20/5. This means that the hawk can see from 20 feet what most people can see from 5 feet. (Scientific American, April 2001, page 24)

 Mice
 

• Can hear frequencies between 1,000 and 100,000 Hz. By comparison, we humans can hear frequencies between 20 and 20,000 Hz.

 Mosquito

• Attracted to host by human body odor ( especially the foot odor), carbon dioxide, body heat and body humidity.

 Octopus
 

• Retina contains 20 million photoreceptors.
• The eye has a flicker fusion frequency of 70/sec in bright light.
• The pupil of the eye is rectangular.

 Penguin
 

• Has a flat cornea that allows for clear vision underwater. Penguins can also see into the ultraviolet range of the electromagnetic spectrum.

 Pig
 

• Tongue contains 15,000 taste buds. For comparison, the human tongue has 9,000 taste buds.

 Pigeon
 

• With eyes mounted laterally on their heads, pigeons can view 340 degrees...everywhere except in back of their heads.
• Can detect sounds as low as 0.1 Hz.

 Rabbit
 

• Tongue contains 17,000 taste buds.

 Rat
 

• Has hearing range between 1,000 and 90,000 Hz.

 Seahorse
 

• Each eye can move independently.

 Scorpion
 

• Can detect air moving at only 0.072 km/hr with special hairs on its pincers.
• Can have as many as 12 eyes.

 Shark
 

• Has specialized electrosensing receptors with thresholds as low as 0.005 uV/cm. These receptors may be used to locate prey. The dogfish can detect a flounder that is buried under the sand and emitting 4 uAmp of current.
• Some sharks can detect fish extracts as concentrations lower than one part in 10 billion.
• Some sharks sense light directly through the skull by the pineal body.

 Snakes
 

• The tongue of snakes has no taste buds. Instead, the tongue is used to bring smells and tastes into the mouth. Smells and tastes are then detected in two pits, called "Jacobson's organs", on the roof of their mouths. Receptors in the pits then transmit smell and taste information to the brain.
• Snakes have no external ears. Therefore, they do not hear the music of a "snake charmer". Instead, they are probably responding to the movements of the snake charmer and the flute. However, sound waves may travel through bones in their heads to the middle ear.
• Snakes have no moveable eyelids. Instead, they have a clear, scale-like membrane covering the eye.

 Spider
 

• Many spiders have eight eyes.

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