Some flightless birds, like the kakapo, seem like they could fly if they just lost a little bit of weight… so I wonder if that’s actually ever happened.
Looking at Wikipedia, the kakapo needs to do more than lose weight. The wings are shorter than normal and they don’t have a keel bone for flight muscles. So there are several sub-surface issues that the birds would need to address to regain flight.
It would be interesting to see if this is caused by regulatory genes (ie, growth is turned off), so that a simple mutation could reverse the loss structures.
I think the answer is no, as far as we know.
I remember studying flightless birds in college and I don’t remember any species that lost the ability to fly ever gaining it back.
And even if a flightless bird was somehow able to fly I’m not sure it would be able to survive since they have evolved for thousands of years to living on the ground.
chickens?
Have not lost the ability to fly, except as far as long distances are concerned. AFAICT there is no domestic chicken variety that has re-evolved the same level of flight ability that their wild junglefowl cousins (which themselves are not much for flying) possess.
The Master speaks on why chickens don’t fly (much).
The first birds to have evolved the ability to fly* must have managed somehow.
*Or the dinosaurs that evolved the ability to fly, and then evolved into birds, or however it went. Either way, their ancestors lived on the ground for a long time before they became fliers.
Most birds that have lost the ability to fly, with the exception of the ratites, are restricted to small islands. They usually lost flight because there were no predators on the islands, and because food could be easily obtained by walking. Individuals that flew would be more likely to be blown out to sea. So there was little selective advantage for flight, and a significant disadvantage.
For flight to re-evolve in these species, some new conditions would need to develop that made it advantageous once again to fly. However, when predators reach a new island, they usually knock off the flightless birds so fast there isn’t nearly enough time for selection for flight to take place.
If flightless birds, which are clearly very closely related to their flying ancestor, cannot regain their capability to fly, then how could the capability to fly emerge from a (flightless) ancestor of a flying bird, which could be evolutionarily more distant from its flying descendant than the flying bird is to its (flightless) descendent? Said more simply, how could flying develop in the first place when it cannot even do so in flightless birds? Wouldn’t it be expected for flight to be most readily acquired by a species that had already in its past possessed that ability? Doesn’t this potentially mean that evolution is unidirectional and irreversible, which seems to contradict the modern consensus on evolution.
Secondly, do all flying birds have the evolutionary potential to become a flightless bird, provided they are placed under certain conditions? i.e. the dodo is a flightless bird, and its ancestor was a bird that could fly. Could an eagle, hummingbird, falcon, etc. potentially become a flightless variant, or is this transition limited certain birds, such as the ancestor to the dodo?
I’m pretty sure that any bird population that became isolated long enough in a place with a food and predator profile that allowed it to thrive without flying, would become flightless. Flying takes energy and requires some compromises in body design; the ability will only be selected for when it is necessary to overcome the terms of the local environment.
Interestingly, there is evidence that the surviving ratites are more closely related to their still-flying relatives the tinamous than they are to other ratites, which can only mean that the power of flight was lost several times in several mutually-isolated populations.
Reacquiring flight, or acquiring flight in the first place, is more of a trick. The first flying ancestors of modern flying birds had more time, reason (competitive pressure) and opportunity (numbers and distribution) to stumble across the right mutations than any flightless population has had to go back.
What do you mean, “cannot”? Ain’t nobody here (or anywhere else AFAICT) saying that bird species that lose the ability to fly CANNOT re-develop that ability under the right evolutionary conditions. Merely that it seems never to have happened to any known flightless bird species, because the required conditions are very unlikely.
Birds, bats and insects have all separately evolved the ability to fly, so there’s no question that it can be done, and no reason it couldn’t be done again by some species experiencing the right selection pressures. But as other posters have pointed out, it’s unusual to see such selection pressures arise for a species that previously found flightlessness more advantageous than flight.
This is the same reason why Pekin ducks don’t fly far: The Chinese breeded mallards for more fat, and the Pekin duck is the result. (The Pekin ducks are those white ducks you see on ponds.)
What are these selection pressures? I’m thinking of this thought experiment: take a whole bunch of chickens, and take a certain percent that has the largest wing length to weight ratio from each generation, let this selected group breed with each other, and then repeat for 10 generations. If selection pressures exist that could conceivably lead to flightless birds regaining flight, couldn’t some artificial selection procedure accelerate this transition? (I’m not saying that the procedure I suggested above would be a valid selection procedure).
What you’d be doing here is selecting for larger wings, not flight. Large wings are necessary but not sufficient for flight. There are lots of other changes involved, including alterations to the skeleton, musculature, and metabolism. Not being Colibri, I have no idea how many of these changes the average chicken already has or lacks.
If you want to artificially select for flight, then select for flight. Drop a bunch of chickens out of a hot-air balloon, and only allow the 10% that land farthest from the drop site breed. Or something.
The problem here is that chickens DO fly. It’s trivial to breed/select for better flight, but it’s virtually impossible to go from flightless to flightful (if you’ll allow me to create a word there).
The better thought experiment would be breed penguins based on wing length and see how long it takes them to fly. If it ever happens, it’d take more than 10 generations, that’s for sure. More significantly, you’d be working with selection pressures that would make no sense in nature, since you’d have generations of intermediates that suck at both swimming and flying and depend on humans for food. (If we were to use Smeghead’s example of throwing birds out of a balloon, all you’ll select for in penguins will be thick skulls. You can’t select for flying in a flightless population.)