CONTENTS Reptiles amphibians worms and mollusks How do we see Mammals Birds Insects Glossary Index List of sources 3 7 17 23 29 34 34 35
HOW DO WE SEE Below is a scene viewed through human eyes But what about the other animals in the picture Do they see the same thing Some animals have a wide field of vision but others have a narrow one Some see fast movements and others can only perceive motion when it’s slow Some animals see the world in many colors others only see one or two Some can make out lots of detail others move through a world of fuzzy shapes Look out for the symbols below to learn more about how animals see Field of vision How much of their surroundings animals see depends on where their eyes are on their heads Light and color When light enters our eyes it hits the surface at the back of the eyeball This surface the retina is Predators such as tigers and wolves have eyes that face forward They see very well in front of them Prey animals such as deer and cows have eyes on the sides of their heads They see much better what’s around them keeping a lookout for hungry predators 180 degrees 360 degrees Humans have a field of vision of 200 degrees This means we see just over half of the circle around us This system allowed our ancestors to spot danger to the sides Our vision has three areas In the one on each side we see with only one eye But in the area in the center we see with both eyes at once called binocular vision In this zone we see objects in 3-D and judge distances best Capturing movement To see movement our eyes take still snapshots Then our brain puts them together to make a sequence Humans take about twenty of these snapshots per second But some animals take as few as four snapshots per second This means they can only see much slower movements than we do Others take as many as 300 They can see movements so fast that they are invisible or very blurry to us covered in special cells that capture light There are two types of these cells called rods and cones Rod cells only detect light’s brightness But cone cells detect wavelengths of light and convert them to colors We are used to the rainbow of colors we see but many animals cone cells are different from ours This means some see fewer colors than we do Others see lots more including ultraviolet and infrared ultraviolet violet blue green yellow orange red infrared invisible to humans colors visible to humans invisible to humans Sharp or blurry Some animals can see in sharp focus Others travel through a blurry world For most animals in this book sharpness depends on three things the size of the eye the shape of the lens that focuses light and the number of rod and cone cells on the back of the eye
THE EYE Nature’s camera Eyes come in lots of different shapes Human eyes are round like a ball Other animals can have flattened or tube shaped eyes Simple eyes Compound eyes Human Eagle Lizard Ant How the human eye works The lens is a see through layer of tissue that focuses the light Many animals can change the shape of the lens to focus on objects at different distances The cornea is a thick see through covering that protects the eye The iris is a ring of muscles that can open or close This lets more or less light through the hole in its center called the pupil Seeing with your brain We don’t just see with our eyes we need our brains to decode the information The retina is a thin layer at the back of the eye It is covered in light sensitive cells called photoreceptors that capture light and detect color Humans have more than 130 million photoreceptors in each eye The image is upside down on the retina but our brains turn it the right way up Photoreceptor cells come in two types rods which allow us to see lightness and darkness cones which allow us to see color The fovea centralis is the most light sensitive part of the retina More photoreceptors are concentrated here than anywhere else This allows it to capture the sharpest image First the rods and cones break down the image into electrical signals that are sent to the brain Each side of the brain receives information from both eyes The brain interprets this information and creates an image The whole journey from eye to brain takes less than a second
WHAT ANIMALS SEE The world through animals eyes Do dogs see in color Can cats really see at night How do insects find flowers Which animals have better vision than we do Scientists perform experiments to learn how animals see They have looked through the eyes of bugs painted beehives different colors and shown pictures to chimpanzees They have even released bats into the air with blindfolds on Scientists have learned a lot from this research But there is still plenty to discover Let’s take a look at the world through animals eyes Why see at all That depends on the animal Sight can help animals explore find food escape from predators and avoid bumping into things It can aid a predator in catching its prey or a bee in its search for flowers Sight can also help animals find members of the same species and communicate with them 5 Other senses Animals have lots of senses for finding their way through the world Vision is important for humans and other apes But many animals depend on other senses Smell taste hearing or touch can be just as important If an animal can’t see well its other senses are often more developed
