Whenever we find birds living, so to speak, lives of languorous 
ease—where there are no enemies to be evaded, where there is an 
abundance of food to be picked up on the ground all the year 
round, and the climate is kindly, there flight is no longer practised. 
Year by year, generation after generation passes by, and no use 
whatever is made of the wings. In all such cases these once most 
vital organs dwindle away, and finally vanish. We can trace 
every step in this process of decay. 
We may begin with the “ steamer-duck ” of the Falklands. 
In this species, after the first moult, the power of flight is lost for 
ever. Among living birds only a few species, apart from the 
ostrich-tribe, are in this dolorous case. The owl-parrot, or kakapo, 
of New Zealand, is one of these. A grebe found only on Lake 
Titacaca, perched high up a mountain-side is another. In both 
these birds the keel of the sternum is represented by the merest 
vestige, the breast-bone being reduced to the condition found in 
the ostrich-tribe. 
The two giant pigeons, the dodo, and its cousin the solitaire, 
afford instances where the loss of flight has been followed by 
extinction ; owing to the invasion of their haunts, through the 
agency of man, by pigs and other domesticated animals, which 
destroyed their eggs and young. 
The ostrich-tribe is peculiarly interesting : owing to the fact that 
their wings present a really wonderful series of degenerating stages. 
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