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Hi Geoffrey,
On another quite different tack: It is worth
mentioning that the family Rallidae, of which our crakes are small ones, but
includes swamphens, coots, moorhens etc, are especially prone to dispersing to
widespread sites. So this is quite consistent with your suggestion. Not only
that, but many of them fly to reach isolated islands and if there are
no ground predators there, they are especially prone to then evolving
into flightless forms. This is partly because of aspects of the embryology of
the Rallidae, in that their wings develop late in their embryology, compared to
say the galliformes and other precocial hatching birds. With that aspect, it
becomes easier (in an evolutionary sense) to suppress the development of the
wings, and thus achieve flightlessness.
Philip
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