Late_Cretaceous

THis is pure speculation.
Most examples of how flight evolved in birds offers a scenario of feathered dinosaurs running to catch insects and flight being of an advantage. THe thing is, how many of today's birds use running to take off? Are any animals in nature obseved to use running take-offs in order to catch prey? If it was an effective method, it may very well be seen in some of today's species (avian or not). Somehow the image of a running feathered dinosaur leaping into flight to catch a bug just doesn't gel with me. Wouldn't the transition from running to flying slow an animal down enough to let the prey escape? I suppose this scenario makes sense since birds evolved from cursorial animals, as opposed to arboreal ones (so that may rule out gliding from tree branches).

But here is another scenario, and one that I have never seen presented before. What if feathered dinosaurs flapped their forlimbs vigorously for mating competitions or to attract mates? Some evidence suggests that these feathered dinosaurs moved their forlimbs in a very similar manner to flapping-flight. WHat if flapping ones' forlimbs rapidly, along with showy plumage, was what what it took to get lucky for these guys? Perhaps in some species a short sustained flight was required in mating rituals/combat.

Vorkosigan

Actually, when one thinks of the other "runaway" traits like peacocks' tails and giraffes' necks that result from sexual selection, this sounds almost plausible. Too bad behavior doesn't fossilize.

Vorkosigan

liquid

Just to update you on some flight-evolution theories...

1) ground up, as you mention. Animals running, perhaps to escape predators, find proto-wings assist their leaping. We certainly see the leaping escape behaviour (e.g. gazelles), we certainly see proto-wings aiding escape (flying fish and hatchet fish). It doesn't seem particularly relevant to birds, but many do run slightly to take off, e.g. chickens. However, the running behaviour might just be lost as redundant.

2) tree down. Gliders find their proto-wings aid tree-traversing. Examples are sugar gliders, gliding snakes and frogs. Protowings might have evolved for all sorts of reasons first - for instance, bats can use them to catch insects.

3. up trunk. A new theory states that protowings help with running up tree-trunks, by creating a downforce (sideways actually!)and perhaps a little lift that sticks the animal to the trunk as it climbs. Sounds a little silly, until you realise that it is exactly the mechanism many young birds use to get back into the tree after a failed first attempt at flying. Grouse adults sometimes do it too.

Mating display would be a good reason for the formation of a protowing, but the theories above exaplain how these might have developed into full flight wings.

There are plenty of other possibilities - insect catching, shading (some african fishing birds use them to create shadows to attract fish), heat regulation, gliding as mentioned etc etc.

Coragyps

I'm going back to some Disney nature movie of 40 years ago for this, but there's at least one waterfowl species - swanlike, maybe - that "runs" across the water to build enough airspeed to fly. I think the display scenario sounds reasonable, but I see no reason that flight couldn't have arisen in two or three different ways among feathered critters - pick a couple of those liquid mentioned. Nature seems way too multifaceted to me to hold her to just one way to do things!

KeithHarwood

Depends on the bird. Many birds, but particularly small ones in woodland areas can take off from a standing start. They clap their wings together over their backs so that there are very strong air currents flowing over the wings before they move.

At the other extreme are the large, long distance ocean flyers. These can't clap their wings, in fact they can barely raise them above horizontal. These birds need a long runway to take off and you see them behaving like 747s at an airport; they taxi out to the runway, they face into the wind, they start a take-off roll, running and flapping wings, once they get enough speed for ground effect to operate they retract the undercarriage and slowly gain enough height to make a slow turn into the direction they want to go. Landing is even more of a problem. They come in to the runway at an incipient stall, but they are still travelling faster than they can run, so it's like landing with the undercarriage brakes on. If 747s landed like that we would use up an awful lot of 747s.

In between we have birds that can take off from flat ground with a small run, but prefer dropping of branches or cliff faces. And of course there are lots of other variants.

Swans do appear to run across the water while taking off, but it's not to provide thrust, it's to reduce the drag of the feet in the water while they are getting to flying speed.

Jerry Smith

Has anyone proposed mammal predation of dinosaur eggs/hatchlings as a possible selection for tree-nesting? Would that lend any weight to trees-down hypotheses?

liquid

Jerry, although I cannot say for sure, I would imagine yes, and yes.