I'm no bird expert, but did 20 years competing hang
gliding around the world, before really getting into
gliding.
Hang gliders mixed with (soaring) birds far more than
sailplanes. Probably a performance thing.

The birds seem to do different things depending upon
the task at hand.
IE: want to gain height quick - they'll be in the best
core or thermal within the vicinity. Want to go somewhere-
they'll be heading towards the next thermal that optimises
their route. Want to 'hang out' they'll be in any old
lift.
I witnessed the whole USA hang gliding team joining
a flock of circling Orubu in Brazil. They all landed
next to the dead cow.
Larger raptors can be more territorial and therefore
don't have the same choice on area, thus might put
up with inferior lift.
Storks just seem to follow the leader.
Swifts and Swallows are almost always in good cores,
but I haven't a clue how they transit between thermals
so quickly.

The soaring birds not only find the best cores, but
seem to very quickly know where the next thermal is.
Many times I've watched their transiting direction
- always dead straight - and altered my course to intercept
or get ahead. It usually works.

When we fly a lot, we pick up those extra sensory inputs
- the micro turbulence, the twitch of the wing - it
gives us huge amounts of info if we're open to it.
By the end of the soaring season, I've sometimes just
known where the core was by feel - which way to turn,
etc. I don't know how - just intuitive. Birds fly all
the time, so should be totally tuned in.
Lastly, I'm sure they plot sink. We tend to focus on
lift, whereas, of course, it's just a part of the equation.
If you know where the sink is, then happy days, avoid
it!
Pete Harvey

A falconer at the Parowan regionals last week told
us that soaring birds have sensory organs that are
able to measure the pressure differential between the
outside air and inside their hollow bones. I have not
been able to confirm this, but it would seem to make
sense - think of the bones as capacity bottles.

Any bird experts out there?