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Re: More on Argentavis
I find it interesting that in the size range of about
3-10 cm, hovering flight seems to have been far easier
to achieve than in larger or smaller animals.
Dragonflies, hawkmoths, hummingbirds, small passerines
Those are actually the larger animals capable of continuous hovering
(much larger species can sustain hovering for short bursts. Pandion is
probably the largest hovering-adapted living species). Tiny insects
can also hover. However, at very small sizes, staying still in the air
column will be very difficult if it has any shear gradient at all (i.e.
any gusts whatsoever). In addition, the very smallest insects can stay
aloft in the air column without the need for energetic hovering as
required in the above listed species.
I'm not sure, but small bats don't seem to do it; may have
something to do with the fact that their wings are
attached to the body over a long distance and don't
have sufficient freedom to move.
A fair number of bats hover; mostly nectar feeders.
But from my totally unscientific observations of
living animals, I get the impression that wing
movement during hovering in dragonflies *looks*
different than in hawkmoths, let alone hummers.
Dragonfly hovering is indeed a bit different, partly due to the use of
four active wings versus two (hawkmoths mostly hover with the
forewings). Still, the basic similarities are there in terms of
momentum changes. Dragonflies do have a tendency to rotate sharply in
an almost exactly horizontal plane while hovering, though, which seems
to be rare in hummers and hawkmoths.