The Linnaean system of classification organises all living organisms into a hierarchy, progressing from the most general to the most specific groups. This system comprises eight levels: domain, kingdom, phylum, class, order, family, genus, and species.
Birds are classified under the biological class Aves. This class is further divided into orders, which group birds with similar characteristics. Some of the largest orders include landfowl (Galliformes), waterfowl (Anseriformes), shorebirds (Charadriiformes), falcons, (Falconiformes), owls, (Strigiformes), dirunal birds of prey (Accipitriformes), parrots (Psittaciformes), and perching birds (Passeriformes). Among these, Passeriformes is the largest order, containing more species than all other bird orders combined, and the largest single order of land vertebrates.
Within each order, families represent groups of species and genera that are more closely related to each other than to any others, sharing a common ancestor. While families were traditionally classified based on morphological traits, modern classifications increasingly rely on genetic data for accuracy.
The International Ornithological Congress (IOC) currently recognises 44 orders and 256 families of birds, 82 of which are found in the British Isles.
