Noun
flightless birds having flat breastbones lacking a keel for attachment of flight muscles: ostriches; cassowaries; emus; moas; rheas; kiwis; elephant birds
Source: WordNetRight wing (definition): As with the left wing, half the propulsive force of a flightless bird. Richard Summerbell
The emu was a large, flightless bird which shared the habitat of the thylacine and was hunted to extinction around 1850, possibly coinciding with the decline in thylacine numbers. Source: Internet
When the journal was published in 1646, it was accompanied by an engraving of a dodo from Savery's "Crocker Art Gallery sketch".sfn A white, stocky, and flightless bird was first mentioned as part of the Réunion fauna by Chief Officer J. Tatton in 1625. Source: Internet
The kiwi is a highly active, if specialized, flightless bird, with a stable body temperature and a fairly low resting metabolic rate, making it a good model for the metabolism of primitive birds and dromaeosaurids. Source: Internet
The ribs are flattened and the sternum is keeled for the attachment of flight muscles except in the flightless bird orders. Source: Internet