flightless

Flightless describes the state of an animal that is unable to fly. In birds, flightlessness has evolved independently in many lineages and is often linked to long periods of isolation from predators, especially on islands, or to ecological shifts that favor ground-daring or aquatic locomotion. The trait reflects a balance of energetic costs, wing morphology, and lifestyle.

In terms of anatomy, flightless birds typically have reduced wings and a diminished keel on the sternum, which means they lack the large flight muscles needed for powered flight. They often compensate with stronger legs for running or, in the case of penguins and related species, with adaptations for swimming. The loss of flight does not imply reduced overall mobility; many flightless species are fast runners or proficient swimmers.

Among birds, well-known flightless groups include the ratites (ostrich, emu, cassowaries, rheas, kiwis) and various island rails. Penguins are flightless in the sense that they do not fly, yet they are skilled swimmers. Many extinct species, such as the moa of New Zealand and the dodo of Mauritius, illustrate historical examples of flightlessness linked to ecological contexts and human impact.

Conservation-wise, flightless species are often highly vulnerable to introduced predators, habitat destruction, and climate change due to their limited dispersal and small population sizes. Protecting habitats, controlling invasive species, and targeted breeding programs are common conservation strategies. Reversals from flightlessness to powered flight are considered rare and controversial in scientific literature.