Tawny Owl Measurements
On average, Tawny owls measure 38cm from the tip of the beak to the tip of the tail. The wingspan is 99cm.
Females are much larger and heavier than the males, weighing 520g, compared to 420g.
The difference in size means that the two birds in a pair hunt for slightly different size prey, which reduces the competition for food.
Bird skulls are made of light, delicate bone. You can see by the size of the eye sockets, that sight is their most important sense. The beak also forms a major part of the skull.
Owls are renowned for their superior intelligence but they do not, in fact, have a particularly large brain. In bird skulls generally, the brain is relatively small. However, it has been discovered that birds have many more brain cells, or 'neurons', than mammals do, in the part of the brain which deals with intelligence; it may simply be that their brain cells are more densely packed.
The owl skull is predominately taken up with enormous eye sockets, which give them a tremendous field of vision. The eyes face forwards as owls are predators, not prey animals.
Owls have a relatively large area directly in front of their face, which they can see with both eyes. This wide area of 'binocular vision' helps them to pinpoint successfully, the exact location of their prey. Other birds have their eyes further apart, on the sides of their head and they view independently, with each eye.
All birds have a ring of overlapping, bony plates which surround and protect the eyes. Reptiles also have these eye rings and they were present in dinosaurs, millions of years ago.
The eye ring is called the 'sclerotic ring'. It supports the huge eyeball and is made up of a series of vertical plates of thin bone. The large rings enable the owl to have larger eye balls than could normally be contained by its skull; the eyes are deeper and more tube-like. They project beyond the skull, held in place by the rings of bone.
Owls' 'bulging eyes' also make the distance between the front and back of the eye greater, which is good for seeing over longer distances.
Beak & Nostrils
Birds have a tough layer of keratin around their upper and lower 'mandibles', or the beak. (Keratin is what our nails and hair are made of.) This sheath protects the bones at the end of the beak. This is particularly important in owls who may use their beaks to kill large prey items!
The beak is hooked, for holding and tearing up prey. Owls can open their beaks very wide. They will swallow a whole mouse in just two or three gulps! They eat everything, the head, feet, tail and fur!
The holes at the top of the beak are called the 'nares' or nostril. This is where air passes into the bird's lungs.
Birds have a stiff tongue for moving food towards the back of the mouth; they have bones inside the tongue! They have no teeth. Instead, food is broken down and processed in part of the stomach called the 'gizzard'.
The ear hole is directly behind the eye.
Birds do not have ears, or flaps of skin and cartilage like mammals do, which lead to the inner ear. They just have small ear holes which lead directly to the inner ear.
Owls have a phenomenal sense of hearing which is necessary as they usually hunt at night, often in pitch darkness.
The circle of stiff feathers, known as 'facial discs', around the eyes, act like a funnel and direct sounds into the ear holes.
Many species of owl have asymmetrical ear holes, where the ear hole is higher on one side than the other. You can see this on the Little owl skull. This adaptation enables an owl to pinpoint the location of its prey as, while it flies low hunting for food, the rustling and squeaks of the mice and voles, will hit one ear slightly earlier than the other.
The spine is a line of small bones, called 'vertebrae', which link up to form the central column in the animal's skeleton.
In birds, the spine has little flexibility apart from in the neck and tail. This rigidity is important for helping the bird's body resist the forces exerted by the wings in flight.
The spinal cord runs along a tunnel, called the 'neural canal'. It is formed inside the small vertebrae. Nerves branch out from the spinal cord, through gaps between the bones.
The shape of the vertebrae varies, depending on whether they are in the neck, chest, back, hips or tail. The different vertebrae are neck (cervical), chest (thoracic), lower back (lumbar), hip (pelvic) and tail (caudal).
The first vertebrae in the spine are the 'cervical' vertebrae. The 'thoracic' vertebrae connect to the ribs.
In birds, the spine then becomes very different to a mammal spine as all the ' lumbar' vertebrae, the 'sacral' vertebrae and some of the 'caudal' vertebrae are fused with the bones of the pelvis to form one of the largest bones in the skeleton, called the 'synsacrum'.
A few 'caudal' vertebrae extend into the tail, beyond the pelvis.
Birds have such huge eyes, they can barely move the eyeballs within the sockets. To compensate for this, they have evolved relatively long necks, so they twist their head around, instead. They can also use their beak for preening and manipulating food, which is necessary as they cannot use their forearms, which have evolved into wings, for these essential tasks.
Owls have extra neck vertebrae, which allow them to swivel their necks through almost 180 degrees. This is good if they are hunting from a perch or tree, which Tawny owls and Little owls, often do; they can spin their head round if they hear a noise behind them. They also have extra strong neck muscles, so they can twist and tilt the head further than other birds.
Owls look as if their neck is thick and as wide as the body but in fact, that part is made up largely of feathers. See how small the neck bones are, below.
The four bones which form the 'pectoral girdle' are the crucial part of a bird's skeleton, when it comes to flight. The four bones are: the breastbone, or 'sternum'; the 'coracoid' bones; the shoulder blades or 'scapula'; and the two fused collar bones or 'clavicles', or 'furcula'.
Sternum. In birds which can fly, the breastbone is enlarged with a projection, shaped like the keel of a boat; this is where the flight muscles attach. It stabilises the bird's body in flight against conflicting air streams, as the keel prevents a boat from toppling over in the waves.
The two 'coracoid' bones are like pillars, linking the sternum to the shoulder blades.
The long shoulder blades, or 'scapulae', form a surface area for the shoulder muscles to attach onto. They lie back along the top of the ribcage, parallel with the vertebrae. They glide over the surface of the ribcage, as the wings move up and down.
The 'clavicles', or 'furcula', form a U shaped bone in front of the rib cage. This is what we call the 'wishbone' in a roast chicken! As a bird flies, the furcula acts like a spring, reacting to the flapping of the wings. When the wings come down, the furcula is compressed downwards and when the wings rise, the furcula springs back upwards.
A small but vital canal runs through the point where the scapula joins the coracoid bones. The large muscle which is used to raise the wings in flight, lies on the breastbone below the wings. A tendon connected to this muscle, runs through this canal; it attaches to the humerus, the first bone of the wing. This tendon acts like a pulley and allows the humerus to raise the wing, using muscles which are beneath it. Birds have their massive flight muscles located below their body, not spread along the wings.
Birds have a short, deep rib cage. They have 7 pairs of ribs. The first are small and do not attach to the sternum. The next 5 ribs have two sections: the vertebral rib above, joined to the spine, and the sternal rib below, connected to the sternum or breastbone. The final rib does not attach to the breastbone.
In birds, the five central ribs each have a small flap of bone which overlaps onto the next one; these are called 'uncinate processes'. They help to expand the ribcage for breathing and strengthen it against the rigours of flight.
In birds, several of the vertebrae have fused with the pelvic girdle, to form a large and delicately-shaped bone called the 'synsacrum'. These fused bones create a strong, central platform where the leg and tail muscles can attach. They also provide protection to a large part of the bird's inner organs.
The thigh bones, 'femur', join the pelvis with a ball and socket joint, linking into the first of the two holes, visible in the first photo.
Birds' wing bones have a similar structure to the human arm and hand. When not in flight, the wing folds into three, in line with these three sections.
A long upper arm bone, the 'humerus'. The major flight muscles on the breast attach to the humerus, which drives the wing up and down.
Then there are two slimmer, forearm bones, the 'radius and ulna', which twist over each other, as ours do. This means the bird can twist the wing for steering, during flight. The mid wing, or secondary flight feathers attach onto the ulna, the broader of the two bones. You can see slight bumps along the ulna, which is where the feathers attach.
Finally at the wing tip, birds have the equivalent to our wrist, hand and finger bones, the 'carpometacarpus, illustrated below. These bones carry the tip of the wing; the main flight feathers called the primaries, which are the stiffest feathers a bird has. Most of the bones here have fused to form fewer, stronger bones so they can support the outer edge of the wing in flight.
Birds have two very small wrist bones between the forearm and bones at the wing tip. (They are not in these photos.) The remaining wrist and hand bones have fused into one blade-like bone called the 'carpometacarpus'. It has an oval window in it. The thumb bones have fused into one small bone which projects out at the base of the carpometacarpus. This supports the feathers of the 'alula', which is raised when the bird comes in to land, to prevent it stalling, like the flaps which are raised on aeroplane wings.
The bones of the second and third fingers have fused, or almost fused, into one bone at the wing tip. The outermost feathers of the wing, attach here. The bones of the fourth and fifth fingers have been lost completely, as bird skeletons have evolved.
Tawny owls have brown stripes and mottled patterns on their feathers. This creates excellent camouflage against the bark of a tree.
Owls' flight/wing feathers are covered on the top surface with a soft layer of down. This muffles the flapping sound as they hunt, so as not to alert their prey. It also traps air within the surface of the feather, to create a smooth flow of air over the wings; this prevents the owl from stalling, when it is flying slowly, hunting for food.
Almost-silent flight enables the owls to hear the tiny sounds produced by their small mammal prey and approach them undetected. When owls hunt, their wings are level with their ears, so if they make a noisy flapping sound, they would drown out the noises of the prey below them.
Compared with other birds, owl feathers are not particularly waterproof. They can get soaked and then would not work so efficiently. Also, feathers covered in wet hair, would be noisier. For these reasons, owls generally avoid hunting in the rain. Long spells of wet weather can lead to starvation, especially for young owlets.
Owls have a comb-like structure on the edge of the first few feathers, at the outermost part of the wing, the primary feathers. These hooks interrupt the air hitting the front edge of the wing, forcing some air to flow through the feathers and at the same time, reducing the sound.
Legs, Feet & Talons
Like most vertebrates, birds have a long upper leg bone, the thigh bone or 'femur', which connects to the hip with a ball and socket joint. Below that the long, lower leg bone, the tibia has fused with some of the foot bones to create the 'tibiotarsus'. The fibula is like a thin pin, running alongside this bone. The bones of the lower foot have fused to form another medium length bone, the 'tarsometatrsus', which appears to give a bird's leg, three sections.
This extended part of the leg helps the birds when they take off and land and also gives extra leverage when they jump forward, or paddle in the water.
In birds, the knee joint is usually covered in feathers and is rarely seen. This makes it look as if a bird's knee bends backwards, but in fact the part of the leg, which is visible below the body and feathers, is the ankle or heel joint. Birds actually walk on their toes, not on their feet. Birds generally have four toes, three forward-facing and one, equivalent to our thumb, backward-facing.
Tawny owls have relatively long legs, toes and talons. This helps them catch prey in deep vegetation, at the base of the long grasses and plants, which is where the mice, shrews and voles scurry around.
Long legs also give them good reach when catching smaller birds, lizards or frogs.
The skin on owls' toes is covered in circular pads, which help the owl to grip its prey. They rough texture also gives extra protection for walking, landing on branches and plunging into the undergrowth to grab prey. They use their sharp talons to kill their prey with a clench of the toes.
The Collector, Photographer & Author
I am Susanna Ramsey and I have a unique collection of natural history objects relating to our local British Wildlife. Over the last ten years, I have collected an extensive range of skulls, skeletons, bones, skins, feathers, wings, antlers, insect specimens and taxidermy.
From 2010-2018, I took my Collection into local primary schools to display and run science workshops, tying the display into topics in the National Curriculum such as Adaptations, Bones, Classification, Food Webs, Habitats, Life Cycles and Local Wildlife.
In the last few years, I have worked with the leading schools' catalogue, TTS, to create a range of activity packs and teaching resources about our local wildlife. To find out about these, scroll down.
Click below, for other web pages about animal skeletons.
- Bird Skeletons
- Mammal Skeletons
- Mammal Skulls & Teeth
- Tawny Owl Skeleton (here)
- Mallard Duck Skeleton
- Grey Squirrel Skeleton
- Rat, Mouse, Vole & Shrew Skeletons
Web Pages on other topics:
- Insect Wings: A Photographic Study
- Butterfly & Moth Specimens at the Natural History Museum
- Other Insect Specimens at the Natural History Museum
- Fish Bones
- Local Habitats
- British Plants
Especially for children:
BRITISH WILDLIFE PRODUCTS
Explore the range of British Wildlife products created by The Nature Collection and the leading schools' catalogue, TTS. The products are perfect for use in primary schools, nurseries, after school clubs, forest schools or at home with friends and family.
The photo opposite shows some of the cards from the Tawny owl set, in the Birds Discovery Bags.