Do birds have feathers or scales?

Birds have feathers, not scales. Feathers are a unique defining characteristic of birds. All modern birds have feathers, though some species have reduced plumage. Feathers provide birds with the ability to fly, insulation to retain body heat, and coloration for camouflage, communication and display.

What are feathers?

Feathers are complex structures made of keratin, the same protein that makes up hair, nails and scales in reptiles. A feather has a central shaft called a rachis with smaller branches called barbs extending out from either side. Even smaller structures called barbules branch off the barbs and have tiny hooks called barbicels that zip the barbules together into a tight, but flexible, surface.

There are several different types of feathers that serve different functions for birds:

• Contour feathers – These are the feathers that cover the body and help streamline it for flight. They provide a smooth surface and overlap each other like shingles on a roof.
• Down feathers – These are small, fluffy feathers that grow close to the skin underneath the contour feathers. They trap air against the body to provide insulation.
• Filoplumes – These are hair-like feathers with few barbs that are buried beneath other feathers. They are sensory organs that send information to the brain about airflow and positioning of feathers.
• Flight feathers – These feathers are asymmetrical in shape and attached to the wings and tail. They provide the lift and thrust required for flying.
• Bristle feathers – These are the stiff, hair-like feathers around the eyes and mouths of birds. They offer sensory protection.
• Powder down feathers – These feathers continuously shed a powder made of keratin that helps condition and waterproof other feathers.

Scales in birds

While all living birds have feathers, scales can be found on certain parts of birds in the form of:

• Scutate scales – Overlapping scales that cover the legs and feet of most birds. They provide protection and waterproofing.
• Tarsal scales – Larger plate-like scales found on the lower legs and feet of some birds like eagles, falcons and ospreys. They offer armor-like protection.
• Beak scales – Tiny scales that cover the beaks of some birds like ducks, chickens, turkeys and parrots. They help maintain and waterproof the beak surface.

However, scales never entirely cover a bird’s body and limbs the way feathers do. Feathers are always the predominant external tissue on birds. Even penguins, which appear to have scale-like skin, are actually covered in small, densely packed feathers.

The evolution of feathers

Feathers likely evolved from scales on early reptiles over 150 million years ago. In fact, feathers still develop in modern birds from the same germ layer in embryos that produce scales in reptiles. Over countless generations, feathers became increasingly complex and specialized for:

• Insulation – Downy barbules formed early in feather evolution to trap air against the skin.
• Waterproofing – Branched feathers with interlocking barbules shed water.
• Coloration – Melanin pigments in feathers allowed camouflage, communication and mating displays.
• Flight – Asymmetrical flight feathers on wings and tail provided lift and thrust.

The oldest known fossil feathers date back to 150 million years ago. But molecular evidence suggests feathers likely first evolved much earlier in the Jurassic period in small flightless dinosaurs. As birds evolved from feathered dinosaurs, feathers became key to every aspect of their biology and success.

Unique properties of feathers

Feathers provide birds with a range of beneficial properties not found with scales or fur:

• Lightweight – Feathers weigh much less than fur or scales and allow for flight.
• Streamlined – Feathers contour the body for aerodynamics in flight.
• Insulative – Feathers trap air against the skin to retain heat.
• Waterproof – Feathers shed rain and resist water absorption.
• Colorful – Microstructures in feathers produce iridescent colors for display.
• Moldable – Feathers can be fluffed up or sleeked down to regulate temperature.
• Self-repairing – Feathers are regularly molted and replaced throughout a bird’s life.

These remarkable properties of feathers explain why birds have thrived in so many environments from the Arctic to the tropics. Feathers made possible the evolution of birds themselves.

Functions of feathers

The many different types of feathers allow birds to:

• Fly – Flight feathers on the wings provide lift and thrust.
• Swim – Short stiff feathers resist water on aquatic birds like ducks.
• Run – Large wings on flightless birds like ostriches act as sails when running.
• Dive – Interlocking feathers resist water pressure at depth.
• Keep Warm – Down feathers trap air against the skin for insulation.
• Stay Cool – Bare areas allow heat loss in hot climates.
• Mate – Long colorful feathers attract the opposite sex.
• Camouflage – Disruptive patterns hide birds from predators.
• Communicate – Stripes and crests convey information on mood and status.
• Resist Water – Overlapping feathers shed rain and remain dry underneath.
• Sense – Filoplumes and bristles detect air currents and objects.

No other external tissue is as versatile and multifunctional as feathers. Over tens of millions of years, feathers have allowed birds to radiate into a staggering diversity of niches.

Key differences between feathers and scales

While feathers and scales have some similarities in origin and composition, there are many key differences:

While scales and feathers share similarities in origin, composition and structure, feathers are much more complex and specialized for the unique demands of birds.

Examples of feathered and scaly animals

There are no bird species that have true scales covering their body or assist significantly with flight. However some examples of animals with feathers and scales include:

Feathered animals

• Birds – All modern bird species (duck, hawk, ostrich etc.)
• Theropod dinosaurs – Ancestral birds like Microraptor and Sinosauropteryx
• Pterosaurs – Extinct flying reptiles (Pterodactyl, Rhamphorhynchus)

Scaly animals

• Reptiles – Snakes, lizards, crocodiles, turtles
• Fish – Most fish species including salmon, seahorses and eels
• Mammals – Pangolins, armadillos

Today, feathers remain unique to birds while scales are seen in reptiles, fish, and a few unusual mammals. But millions of years ago, the ancestors of birds had both primitive feathers and scales.

Birds with unusual scales

While all living birds have feathers, some species also have unusually prominent scales on certain body parts:

• Cassowary – Large plate-like scales called casques on their heads.
• Toucan – Large keratin scales on their massive colorful bills.
• Ostrich – Scaly legs with two-toed feet adapted for running.
• Hornbill – Casque scales on the upper mandible of the large bill.
• Chicken – Foot scales called scutellae cover their lower legs and feet.
• Parrot – Scutes help reinforce their powerful grasping bills.

However, these unusual scales are adaptations limited to specific body parts and do not alter the fact that feathers cover and define the exterior of all birds.

Conclusion

Birds universally possess feathers, not scales. Feathers distinguish birds from all other animal groups and make bird anatomy and physiology unique. Diverse feather types allow birds to inhabit aerial, aquatic and terrestrial habitats. Feathers likely evolved from reptilian scales but far surpass scales in complexity, insulation and aerodynamic properties. Scales in modern birds are limited to certain body parts like legs and bills and play no major role in key functions like flight. Feathers define birds and explain their tremendous success in adapting to environments across the planet.