Are flightless birds a reversion?

I agree that the ratites (ostriches, emus, moa and their ilk) are unlikely to represent a lineage that "never developed flight". The ratites as a group represent a very small percentage of avian taxa that are flightless. Rails, for instance (family Rallidae, order Gruiformes) represent over two thirds of all known flightless birds. Since all of the flightless rails, as well as other flightless species (there are a number of pigeons, a wren, a comorant, etc) known have very close relations which retain the power of flight, it would be odd if the flightlessness of ratites represented a non-flying evolutionary lineage.Additionally, I prefer to consider secondary flightlessness an adaptation rather than a "loss of ability". Since the biological energy cost of powered flight is apparently quite high, it might be better to consider flightlessness a "plus" rather than a "loss" in those lineages whose genetic plasticity allows this adaptation. In other words, flightless rails can, at least in some sense, be considered more derived than their flighted predecessors.Hope this helps.Edited by Quetzal, : speling and clarity

Hi arach,It makes sense when you think about it. Although there might be other reasons for secondary flightlessness, all (except African ratites - which I guess is why we're having this discussion) flightless birds evolved in locations where flight was no longer a survival benefit either from the predator standpoint (e.g., Genyornis or the phorusrhacoids from South America) or prey. If there ain't nothing eating you and you don't need to catch fleet prey, why bother? I see it as very similar to the loss of sight in cave-dwelling fish and inverts. Obviously I could be wrong, but from an ecological adaptation standpoint, anything that reduces your energy costs is a good thing...

Absolutely. Moreover, when we're talking about adaptation, we have to consider the rather ambiguous concept of historical constraint. It would seem to me (although the dividing line is really tricky), that "losing" wings, for instance, is a lot easier than the major re-wiring that would be required in going from endothermic to ectothermic (or vice versa, for that matter).In addition, the evolution of flightlessness in the rails I mentioned, for instance, took place in anything from a few tens of thousands to at most 1-2 million years maximum (based on the age of the islands they inhabit). Mostly a lot less time probably. Major rewiring could be done, but not that fast. I'm not sure how long it took to develop full endothermy from putatively ectothermic amphibians, but I'd guess quite a while.