[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Science feather strength debate
> > _Confuciusornis_ would have to wait for a breeze
> of the right
> > magnitude and direction in order to pull off this
> Erik makes an excellent point in that some environments the
> "breeze" is *always* there. No waiting. These environments
> may be limited in area, but exist in evolutionarily
> significant time frames.
I wouldn't say "always", though I do know the duration records for hanggliding
were done slope soaring, in Hawaii, and the time exceeds 24 hours.
Many places that are good for ridge soaring, are more like 70% or more of the
days yield at least 3 hours of soarable conditions, with higher or lower
percentages for each season.
There are many animals that are only active for a small part of the day, or go
inactive for significant time periods (hibernation).
I think if a glider that lived in a place where 3 out of 4 days it could ridge
soar for at least 3 hours, it could be viable.
It could even shed its flight feathers for the parts of the year when flying
conditions aren't so good, and the times of the year when its more like 9/10
days, you might find it sporting full flight feathers.
But this is speculation about possible adaptation to a speculative environment,
and I have no idea how one would show such a condition in fossils.
I'm merely pointing out that if they were gliders, and if they made use of the
weather to fly, we might see seasonal variation in flight plumage, as it could
be that during certain seasons, they'd revert to cursorial locomotion.
I am not sure how much modern bird plumage varies with season, but they can fly
year round, but maybe a glider couldn't.
This would be less speculative if we found two more or less identical skeletons
preserving fine details like feathers, with one sporting long flight feathers,
another with reduced/absent flight feathers.
> There is a very high probability that gliding species
> adapted to (as example) a forest environment were
> fortuitously exposed on a daily basis (in mid-flight!) to
> such conditions over the course of th
pecies of flying fish.... some of them have what it takes (aerodynamically
speaking), to ridge soar, as would many tree gliders - maybe not every day, but
at least some.
(some days its so good/ some pilots are so good, that people joke you could
soar the ridge with a sheet of plywood/ the very good pilot could soar the
ridge with a sheet of plywood)
Now if those occasional soarable days for a poor glider, resulted in an extra
meal or two for the day, perhaps on average every other week, I could start
seeing selection for gliders that can better use suitable ridge lift when it is
As it becomes a better glider, the amount of ridge lift/wind that is
"suitable", increases, and the benefits to flying increase, and I'd imagine it
would be a positive feedback loop, until one ran into diminishing returns from
larger, longer wings.
When approaching that point, I think flapping adaptation would eclipse gliding
efficiency adaptations, and a positive feedback loop would set in until they
were fully capable of self powered flight.
Anyway, thats my speculation, it seems as good to me as "maybe the were gliding
from trees with these high aspect ratio wings that couldn't flap worth a damn,
even though we can't see anything that indicates they climbed trees."
I still see a tree glider stage as viable, but I think *C* was way past that
stage based on its aspect ratio, and I don't see a need to kick it back to
tree/ground dweller, just because any flapping it did was not enough to fly
from level ground in stagnant air.