#Most of the world''s flightless birds are either nocturnal and secretive (e.g. the kagu) or large, swift and well-armed (the ostrich). The exceptions are found primarily on islands, and many of these island species have become extinct with the arrival of humans and their domestic animals.
What special biogeographical conditions on islands might permit the survival of flightless birds? Why has the colonization so often resulted in the extinction of such birds? The power of flight has been lost secondarily in representatives of many groups of birds; what are some possible evolutionary advantages of flightlessness that might offset its obvious disadvantages?