Hummingbirds have a very unique skeletal structure that allows them to hover and fly backwards with great agility. Their bones are extremely lightweight and their wings are designed to flap at high frequencies. Let’s take a closer look at the anatomy that gives hummingbirds their remarkable flying abilities.
Overview of Hummingbird Skeleton
The hummingbird skeleton consists of:
- Skull – This contains the brain and sense organs.
- Spinal column – Made up of vertebrae that surround and protect the spinal cord.
- Ribs – Thin, lightweight bones that protect the heart and lungs.
- Shoulder girdle – Bones that connect the wings to the body.
- Wings – Composed of arm bones, wrist bones, and finger bones.
- Pelvis – Hip bones that connect to the spine and legs.
- Legs – Made up of thin leg bones, ankle bones, and feet.
The entire skeleton accounts for only around 4% of the bird’s total body weight. It is extremely lightweight and delicate in order to minimize energy expenditure during flight. Many of the bones are fused or joined together to add strength and reinforce the skeleton during the physical strains of flying.
Skull
The hummingbird’s skull represents about 1% of its body weight. It is small and narrow to decrease aerodynamic drag during flight. The beak is long, pointed, and perfectly adapted for accessing nectar at the center of flowers. Here are some key features of the hummingbird skull:
- Nasal openings are located at the base of the upper mandible rather than at the tip of the beak, an adaptation for feeding on nectar.
- Large orbits to support their large eyes.
- Hinged jaw that allows the upper and lower mandibles to move independently, enabling access to nectar.
- Reduced number of bones compared to other birds, fused together for strength and lightness.
- Minimal ossification, or hardening of cartilage into bone, keeping the skull extremely lightweight.
Spinal Column
The hummingbird has a flexible spinal column that allows great mobility in flight. The vertebrae are small, hollow, and delicate. Here are some key features:
- Cervical vertebrae – Allow the head and bill to move independently of the body, important for accessing nectar while hovering.
- Thoracic vertebrae – Anchor the wings and shoulder girdle. The vertebrae are fused for strength to withstand flight stresses.
- Lumbar vertebrae – Give flexibility to the lower back.
- Caudal vertebrae – Form the base of the tail, allowing tail movements for steering and maneuvering.
- Synsacrum – Fused vertebrae that brace the pelvis.
- Pygostyle – Forms the base and support for the tail feathers.
Ribs
Hummingbirds have very thin, lightweight ribs that enclose and protect the heart and lungs without adding unnecessary weight. Key features include:
- Slim ribs that are partly ossified and very flexible.
- Ribs do not fully surround the body, reducing weight.
- Ribs attach to a bony sternum that projects from the breastbone.
- The sternum provides an anchor point for flight muscles.
Shoulder Girdle
The shoulder girdle bones provide the framework to attach the wings and flight muscles to the body. These bones include:
- Furcula – Also called wishbone, it’s a V-shaped bone that flexibility allows wing movement.
- Coracoids – Two thin bones positioned behind the furcula that anchor wing muscles.
- Scapulae – Form the back part of the shoulder, supporting the wing.
- Clavicles – Anchor the furcula, scapulae, and flight muscles.
These lightweight girdle bones allow extensive mobility and range of motion in the wings.
Wings
A hummingbird’s wings are perfectly adapted for the energy-intensive hovering and backward flight necessary to collect nectar. The wing bones include:
- Humerus – The upper arm bone, short and rotated horizontally for hovering ability.
- Radius and Ulna – Lower arm bones that are fused for strength.
- Carpometacarpus – Bones of the wrist and palm region.
- Digits – Finger-like bones that the flight feathers attach to.
Unique adaptations such as rotational movement of the humerus allow the wings to make the figure 8 pattern required for hovering and flying backwards.
Pelvis
The pelvis bones include:
- Ilium – Upper bones on each side that anchor to the spine.
- Ischium – Lower rear bones that support the tail muscles.
- Pubis – Lower front bones.
The fused pelvis bones provide stability while allowing some flexibility between the spine, legs, and tail.
Legs and Feet
Hummingbirds have small, delicate legs suited for perching rather than walking or hopping. The leg bones include:
- Femur – Upper leg bone.
- Tibiotarsus – Formed from fused tibia and fibula bones.
- Tarsometatarsus – Lower leg/ankle bones.
- Toes – Digits that are usually adapted to allow two forward and two backward facing toes for grip.
Interestingly, 25% of the hummingbird’s total number of bones are found in its legs and feet. Nevertheless, the leg bones are slim and lightweight to minimize impact on flight ability.
Flight Adaptations
In summary, the special adaptations of the hummingbird skeleton for flight include:
- Lightweight, thin, and partially ossified bones
- Reduced number of bones by fusing certain joints
- Joints allow extensive rotational movement
- Shoulder girdle supports hovering wing motions
- Wings optimized for agility and hovering
- Streamlined skull reduces drag
- Flexible spine allows mobility and movement
- Small, minimized legs reduce mass
These adaptations give the hummingbird exceptional flying maneuverability compared to other birds. Their energy-expensive hovering flight requires an extremely lightweight but strong skeletal structure.
Quick Facts
Key facts about the hummingbird skeleton:
- Total of 244 bones
- Weighs 0.8 to 2.5 grams, about 4% of body weight
- Skull makes up 1% of body weight
- Partial ossification of bones
- Specialized shoulder girdle supports wing movements for hovering
- Wing bones compromised 25% of skeleton
- Legs and feet make up 25% of the skeleton
Skeletal Adaptations for Feeding
Hummingbirds have some unique skeletal adaptations related to their feeding behaviors including:
- Long, slim, pointed beak perfect for accessing nectar at the base of tubular flowers
- Flexible skull joints allow the beak and head to move independently from the body
- Tongue is extendable with forked tips to lap up nectar
- Hyoid bones support the tongue
- Jaw muscles are reduced but with enough strength to open/close the beak
These specializations of the skull and tongue bones enable hummingbirds to feed while hovering at flowers as their fast-beating wings keep them suspended in mid-air.
Skeletal Similarities and Differences in Other Bird Groups
The hummingbird skeleton has some features in common with other avian groups as well as unique specializations:
Similarities
- All birds have lightweight, hollow bones for flight.
- Wings, shoulder girdle, and sternum arrangements share similarities across species.
- Skull bones are fused and reduced in number in all birds.
- Vertebrae and ribs protect internal organs.
- Pelvis bones anchor legs and tail.
Differences
- Hummingbird bones are more delicate, thinner, and lightly ossified.
- More vertebrae allow flexibility.
- Wings relatively much larger compared to body size.
- Specialized shoulder joints for hovering.
- Smaller, weaker feet bones suited for perching not walking.
These adaptations give hummingbirds more flight maneuverability compared to passerines, seabirds, birds of prey, and other groups with different lifestyles.
Role of Skeleton in Hummingbird Flight
The hummingbird’s skeletal system plays a vital role in flight by:
- Providing a rigid yet lightweight framework to support flight muscles and distribute aerodynamic forces
- Allowing the large shoulder muscles required for wing movement to attach to the bones
- Keeping the overall body mass low so less energy is required for flight
- Allowing great mobility through specialized shoulder and wrist joints
- Enabling hovering and backward flight through specialized wing morphology
Without its lightweight skeleton and the adaptations for flexibility, strength, and maneuverability, the hummingbird would not be able to hover and would expend much more energy during flight.
Conclusion
In conclusion, the hummingbird has a specialized lightweight skeletal structure with adaptations that enable its unique hovering flight and nectar-feeding behaviors. The bones are slim, delicate, and partially ossified to minimize weight. Joints and shoulders allow extensive mobility and movement of the wings. The wings, legs, and tail are all optimized for agility and energy efficiency during flight. So while tiny, the hummingbird skeleton plays a huge role in making this bird one of nature’s most remarkable flying machines.
