Birds with wings that cannot fly are usually referred to as flightless birds. They have evolved over time in different environments and have adapted to life without the ability to fly. There are several reasons why certain bird species have lost the ability to fly:

1. **Habitat:** Flightless birds are often found in environments where flying is not necessary or is hindered. For example, many flightless birds inhabit islands where there are fewer predators and ample food resources on the ground.
2. **Predation:** Some flightless birds evolved in environments where there were no or few mammalian predators. Without the need to escape from predators, these birds gradually lost their ability to fly.
3. **Energy conservation:** Flight requires a significant amount of energy, and in some environments with limited food availability, it may be more advantageous for birds to conserve energy by not flying.
4. **Specialized adaptations:** Flightless birds may have developed other adaptations that are more suited to their environment, such as strong legs for running or swimming.

It's important to note that not all winged birds are capable of sustained flight. Some bird species have wings that are specialized for short bursts of flight, gliding, or other specific purposes. Evolutionary pressures and environmental factors have shaped the diversity of bird species we see today, including those that can fly, those that can't, and those with limited flight capabilities.
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