The Evolution of Flight.... why are some birds grounded?

there are flying fish, flying squirrels and a flying snake!

Here is my guess, I am not an expert.Flight is energetically expensive. If it is not an advantage then a creature that doesn't try saves energy.You might note that, again and again, when a bird gets into a enviroment with no predators then a flightless form evolves. The Dodo being a famous example. (most of pre human contact, New Zealand being another ).

LOL, MarkIt will, one supposes, turn out to be, like other things, more complex that it first appeared.[This message has been edited by NosyNed, 10-01-2003]