Chickens and ducks are two of the most recognizable types of poultry globally, often raised side-by-side on farms, yet they exhibit stark differences. Ducks are capable swimmers adapted to aquatic environments, while chickens are mostly terrestrial, known for scratching the ground. This contrast leads many to wonder if these birds are related at all. They do share a common ancestry, but their evolutionary paths separated so long ago that they are considered distant biological cousins.
The Shared Avian Foundation
The biological connection between chickens and ducks begins at the highest levels of classification, establishing them both as members of the bird lineage. Both species belong to the Kingdom Animalia, the broad group encompassing all animals. Moving down the hierarchy, they are both classified under the Phylum Chordata, which means they possess a spinal cord at some point in their development.
Their shared identity as birds is confirmed by their placement in the Class Aves, which includes all warm-blooded, egg-laying vertebrates characterized by feathers. Like all members of Aves, both chickens and ducks possess feathers, lay hard-shelled eggs, and have a unique skeletal structure that includes the furcula, or wishbone. This shared foundation confirms a deep evolutionary relationship, placing them within the same major group of animals.
The Key Taxonomic Split
The true nature of their relationship becomes clear when examining the point where their ancestors diverged, which occurs at the level of the taxonomic Order. Chickens belong to the Order Galliformes, commonly referred to as landfowl or game birds. Ducks are classified within the Order Anseriformes, which encompasses all waterfowl, including geese and swans.
These two Orders are grouped together under a superorder known as Galloanserae, which represents their most recent common ancestor. Molecular studies analyzing genetic data estimate this profound evolutionary split occurred deep in avian history. The divergence between the Galliformes and Anseriformes lineages is generally estimated to have taken place between 59 and 97 million years ago (Mya).
This ancient split means that while they share ancestry, their respective lineages have evolved independently for tens of millions of years. The Galliformes lineage, which includes chickens, pheasants, and turkeys, began adapting to terrestrial, ground-dwelling life. Simultaneously, the Anseriformes lineage specialized in aquatic and semi-aquatic habitats.
Physical Adaptations Reflecting Divergence
The ancient taxonomic split created two groups that developed highly specialized physical structures suited for their differing environments. The most obvious difference is in their feet, which is a direct reflection of their primary habitat. Ducks possess webbed feet, with the three forward-facing toes connected by skin, an adaptation that maximizes surface area for efficient propulsion through water.
In contrast, chickens have strong, unwebbed feet with blunt claws better suited for scratching the ground to forage for food and for walking on uneven terrain. Their skeletal structures also reflect their lifestyles. Chickens have an upright body carriage and longer legs, optimized for running and walking on land. Ducks, conversely, have a lower body carriage and shorter legs, which allows them to maintain stability when swimming and wading.
Another key difference is found in the structure of their heads and beaks. Ducks have a characteristically flat, broad bill that is adapted for filter-feeding and dabbling in water and mud. This bill contains small, fine structures called lamellae, which function to strain food particles from the water. Chickens have a pointed, conical beak, which is designed for pecking at seeds, grains, and insects on the ground, lacking the specialized filtering apparatus. Furthermore, ducks have a highly developed uropygial gland, or preen gland, which secretes an oily substance they spread over their feathers to maintain waterproofing, a necessity for their aquatic existence.