The world of Aves, or birds, represents a vast domain of biological diversity. Understanding the number of birds requires using the specific classifications employed by ornithologists. This structure helps categorize the variety of feathered life found across the planet.
Clarifying Terminology: Species vs. Domestic Breeds
The term “breed” applies to domesticated animals, such as dogs, cattle, or poultry like chickens, that have been selectively bred by humans for desired traits. These breeds exist within a single species; for example, a German Shepherd and a Chihuahua are both members of Canis familiaris. Truly domesticated birds, like the turkey or common chicken, have breeds, but they are relatively few.
In contrast, the term “species” refers to naturally defined populations distinct from one another, generally recognized by their inability to interbreed successfully in the wild to produce fertile offspring. Bird classification focuses almost entirely on these distinct units, which represent the product of natural evolution rather than human selection. The scientific count of avian life relies on the number of unique species, not domestic breeds.
The Global Count of Bird Species
The accepted count for bird species worldwide hovers between 10,800 and 11,200. Authoritative bodies, such as the Cornell Lab of Ornithology’s Clements Checklist and the International Ornithologists’ Union (IOC) World Bird List, maintain these global inventories. The slight variation is due to differing taxonomic philosophies regarding what constitutes a distinct species.
This figure is constantly changing, as avian taxonomy is a dynamic field benefiting from new technologies. Advances in DNA sequencing and vocalization analysis have led to the “splitting” of what was once considered a single species into two or more distinct species. For example, researchers may find that two populations looking nearly identical (cryptic species) are genetically distinct and reproductively isolated. While new species are rarely discovered in well-studied areas, remote regions may still yield a few new species each year.
Organizing Avian Diversity: Orders and Families
The thousands of recognized bird species are organized using taxonomy, a hierarchical system that groups organisms based on evolutionary relationships. The class Aves is divided into Orders, which contain birds sharing fundamental biological characteristics and ancestry. The IOC World Bird List currently recognizes around 44 distinct Orders of birds.
Within each Order, birds are further classified into Families, consisting of species more closely related to each other than to members of other Families. The scale of avian diversity is illustrated by the Order Passeriformes, the perching birds or songbirds, which alone accounts for more than half of all bird species, numbering over 5,000. In contrast, some Orders, like Struthioniformes (Ostriches) or Rheiformes (Rheas), contain only a handful of species, highlighting their distinct evolutionary paths.
Geographic Distribution of Bird Species
Avian species richness is not distributed uniformly across the globe, but shows a pronounced concentration in specific regions. This unequal distribution is linked to the Latitudinal Diversity Gradient, a pattern where biodiversity increases closer to the equator. The highest concentrations of species are found in tropical regions, particularly in lowland rainforests and mountainous areas.
The Neotropics, which include Central and South America, are the world’s primary center of avian diversity. Countries like Colombia and Peru hold the highest number of bird species globally, often exceeding 1,800 or 1,900 species within their borders. This concentration is supported by stable, warm climates and complex habitats, such as the Andes mountain range and the Amazon Basin, which encourage specialization and speciation.