Bird Anatomy

Learning the anatomy of birds gives clues to where they live and what they eat.  Learning the shapes and silhouettes of birds is helpful in identifying them at a distance.

Designed for flight


Birds are one of the few animals that have developed the ability to fly.  Every part from the skeleton to the feathers has evolved to aid in flight.  The skeleton, while using the same general design of other vertebrates has some distinct differences.  The skull is very light in proportion to the rest of the body because there are no teeth for chewing, or any heavy jaw or jaw muscles.  The job of grinding up food is performed by the gizzard.  This means the skull is usually around 1 percent of the body weight.  The bones are hollow with strut like structures inside. This makes them light while still making them strong enough for flight.  The forelimbs have developed into wings.

The wings are composed of the humerus or upper arm, and the radius or ulna, which makes up the forearm with wrist, and hand bones.  The forearm supports the secondary feathers, and the fused wrist, and hand bones support the primary feathers.  The joints have added strength because they have limited movement.

The skeleton has many modifications to allow birds to walk on their hind legs.

The muscles have also evolved for flight.  The important muscles for flight run between the upper arm, and the breast.  There are two pairs of flight muscles.  The larger pair called the pectoralis major contracts for the down stroke. The pectoralis minor handles the upstroke, which needs far less power.

The body is the third part of this design for flight.  It is very streamlined to reduce friction.  The smooth surface of the feathers reduces the friction even more.

The tail consisting entirely of feathers aids in maneuvering. The legs will usually be tucked under the body when flying so they don't affect the flight.

Beaks Legs and Feet

Beaks of birds are varied depending on the species, and are specialized for their particular diet.  In most birds they are light to save weight for flight.  Bird beaks are bony structures covered with keratin, much like our fingernails.

Just like bird beaks, the feet and legs of birds are specialized depending on each bird's habits, and life style.

Here are examples of a few of the specialized beaks and feet.

Drilling Holes  The hard beak of a woodpecker is good for drilling holes.

Birds with short thin beaks usually eat insects.

Cracking seeds  A thick short, or conical beak is good for cracking seeds. Buntings, Cardinals, Grosbeaks, Towhees, Finches ...

The bills of crossbills have lower and upper mandibles crossed, making it easier for them to eat pine cone seeds.  They start at the bottom of a cone and spiral upward, opening each scale, and removing the seeds with their tongues.
Parrots have a different kind of conical bill good for Cracking seeds.

Scooping   A pelican's pouch is used to scoop fish.  When the fish is caught the pouch contracts to squeeze out water.

Birds such as thrashers and wrens, with slender curved bills can probe for insects.

Straight slender bills are very versatile. Large birds like crows are often omnivorous.  Small birds will feed largely on insects. Blackbirds, Bluebirds, Chickadees, Crows, Grackles, Jays, Magpies, Mockingbirds, Meadowlarks, Orioles, Robins, Thrushes,

Humming birds have long thin beaks for getting nectar from flowers.

Birds such as ducks use their webbed feet to swim and their flat beak to filter food from water.

A broad flat bill such as that of flycatchers, shrikes, or waxwings is good for catching flying insects.

Birds like hawks, owls, or eagles have sharp hooked beaks, and powerful claws for tearing meat, and eating other animals.

Bird Feet and Legs Birds that have long legs such as the heron walk or wade more than they fly. Most birds have four toes, three that face forward, and one rearward.  Birds that have two toes facing forward and two toes facing rearward usually hang onto the sides of trees. Birds that swim like ducks will have webbed feet. Predatory birds like eagles, and hawks will have strong talons.  They are usually not very good runners. Here are a few of the many varied types of feet.

Bird Brain

The brains of birds have also developed for flight.  The cerebellum is the part that is responsible for co-ordination of movement.  Because birds make extremely fast moves at very high speeds this part of the brain is large.  The cerebral hemispheres, which let the bird perform complex behavior patterns is also very large.  It turns out that many birds are quite intelligent even using tools and having social communication.

Digestive system

Birds are very active animals.  They use a lot of energy, and consume food at a very rapid rate.  Small birds may eat a third of their body weight in a day. They have specially evolved digestive systems with organs like the gizzard, not found in other animals.

Birds can be herbivores, carnivores, or omnivores.  The herbivores feed on seeds, fruit, and other plants, and have a more complex digestive system then carnivores, which feed on meat.

Lungs

Another thing that is different in birds are the lungs.  In other vertebrates the lungs consist of sacs.  Birds have extensions to the lungs called air sacs.  Inhaled air passes through the air sacs and back thought the lungs.  With this system, oxygen is transferred to the blood during both inhalation, and exhalation.  This gives bird's better use of oxygen for flying, and it allows them to get by with smaller lungs than other vertebrates.  This also aids birds that dive, and need to hold their breath for long periods.

Sight

Birds eyes are much larger in relation to their heads than ours, giving them the ability to see fine detail.  They process what they see faster than we do, and they are better at detecting movement.  Birds can’t roll their eyes like humans so they must turn their heads.  When a robin cocks its head to one side it is looking in that direction.  Having both monocular and binocular vision, bird’s eyes work together to see straight ahead as well as working independently.  This gives some birds an extremely wide field of vision, even allowing some birds to see both in front, and in back of themselves.  Birds such as waterfowl, or pigeons have very little binocular vision, and wide monocular vision.  Some birds such as the kingfisher have droplets of color oil in the retinas that diminish the glare of water when they are fishing.  Others such as raptors have eyes more towards the front of their heads giving them better binocular vision, letting them judge distance better.

Plumage and Colors

While their colors are a thing of beauty to us, these distinctive colors are important to the survival of birds.  Their colors help them attract mates, and protect them from predators.

Females of most species choose their mates, and are attracted to the male with the most colorful plumage.  The color of the male will become muted when breeding season ends.  The female will usually be duller than the male, and this helps protect her from predators while she is nesting.  The markings of many birds give them camouflage allowing them to blend in with their surroundings.  A ruffed grouse matches his surroundings so well it becomes almost invisible.  Many birds have counter shading to help protect them.  The back, which is exposed to light, is darker than the breast, which is in shadow.  The shade of sides will fade gradually from light below to dark above.  Many birds have lighter under parts, and darker upper parts.  This gradual change in color makes them less conspicuous. All adult birds molt at least once a year.  Molting is a process where old feathers are replace by new feathers.  As much as a third of the bird’s body weight is replaced during molting so they need a lot of protein.  Many song birds molt near the end of the summer, and they can look a bit ragged at this time.