Circling for rodents?

It's a well known fact that birds bones are very light and filled with
holes, just like we have sinuses in our head bones. I've pondered how birds
might sense rate of climb many times and I now hold the view that they sense
it via the cavities in their bones - this would provide them with a very
sensitive variometer, the capacity being automatically incorporated so to
speak.

Some work was done in the early 70's on this. Whatever a bird's "vario" is, it resides in
their ear. Cutting the 8th cranial nerves (which connect the ear to the brain)
extinguished their ability to sense altitude. This work was done in pigeons, (not soaring
birds, who would be expected to have an even better "vario"). Further work (done in a
pressure chamber) indicated that even a pigeon can sense an ambient pressure change
equivalent to climbing 2 feet.

I'm also convinced that birds soar for pleasure as well as because they
might have to (e.g. Pelicans soar when they are migrating and follow similar
climb/glide patterns to us).

Other research done in the 70's was carried out by a glider pilot in Africa. He wanted to
figure out where all the buzzards went during the middle of the afternoon (all would
disappear every day). They thermaled up, out of sight from the ground. Either for
pleasure,or to cool off?

"Jim Skydell" wrote in message
...
Other research done in the 70's was carried out by a glider pilot in Africa.
He wanted to
figure out where all the buzzards went during the middle of the afternoon (all
would
disappear every day). They thermaled up, out of sight from the ground. Either
for
pleasure,or to cool off?

Or simply because it takes little energy and makes them temporarily safe
from all ground-bound predators?

Vaughn

I'm also convinced that birds soar for pleasure as well as because they
might have to

Earlier this year sitting in my garden on a hot windless day, I watched a
Buzzard pick up a thermal over a small local wood and climb until it was a
speck in the sky. It then closed its wings and dived at great speed until it
was about fifty feet above the ground, pulled out and then proceeded to
climb again. It repeated the climb, dive, climb manoeuvre three times before
I went indoors. Surely that could not have been for anything other than
pleasure ?

DB

"Silent Flyer" ] wrote in message ...

I'm also convinced that birds soar for pleasure as well as because they
might have to

Earlier this year sitting in my garden on a hot windless day, I watched a
Buzzard pick up a thermal over a small local wood and climb until it was a
speck in the sky. It then closed its wings and dived at great speed until it
was about fifty feet above the ground, pulled out and then proceeded to
climb again. It repeated the climb, dive, climb manoeuvre three times before
I went indoors. Surely that could not have been for anything other than
pleasure ?

DB

Definitely not. I have watched similar behaviour many times. One
particular time I was climbing under an nice fat cu where three
buzzards were climbing in to the cloud out of sight and then diving
out of it about five seconds later, over and over again.

Marcel
-------------
Why walk when you can soar?

??Back in my hang gliding days I participated in a competition at ?Grandfather Mountain in North Carolina - about an 800 foot cliff ?followed by another 800 feet of mountain Ð and the cliff was part of a ?soarable ridge. Grandfather mountain is a tourist attraction with a road ?to the top and a gift shop at the summit. We knew we weren't going to ?soar that day because we had trouble walking into the gift shop. The ?weather station inside was reporting winds in excess of 90 mph. But the ?wind direction was perfect - dead on the ridge.??We didn't soar that day but the local residents did. They have ravens at ?Grandfather mountain - lots of ravens. We were literally hanging on to ?any thing we could because we were afraid of being blown off the ?mountain. And, walking across that suspension bridge between the 2 peaks ?was probably not the smartest move. Anyway, the ravens were soaring the ?flippin' ridge. They had their wings tucked in real close and were just ?zipping along. T
hey were at ridge top level about 30 feet in front of us ?and it was just amazing. I can only guess at what their airspeed was, ?but they were probably moving across the ridge at 20 to 30mph and so ?when you factor in the 90+ mph wind speed, their ASIs were probably ?hitting near 130. You'll never convince me they were flying to catch ?lunch - they were flying because they were having a blast. Of this I ?have absolutely no doubt.??Tony V. LS6-b "6N"?

In article , Tony Verhulst
flippin' ridge. They had
their wings tucked in real close and were just ?zipping along. T
hey were at ridge top level about 30 feet in front of us ?and it was just
amazing. I can only guess at what their airspeed was, ?but they were probably
moving across the ridge at 20 to 30mph and so ?when you factor in the 90+ mph
wind speed, their ASIs were probably ?hitting near 130. You'll never convince me
they were flying to catch ?lunch - they were flying because they were having a
blast. Of this I ?have absolutely no doubt.??Tony V. LS6-b "6N"?

I wonder what Vne is for a raven?
--
Mike Lindsay

So, if the experiment had them sense the altitude in a pressure
chamber, and if whatever they use for thermalling is the same as
sensing altitude, this precludes all the "G-force" and vertical
accelerometers theories mentioned he you can fool a vario in a
stationary pressure chamber, but not an accelerometer ...
Going back to the ears: do birds' ears connect to the nasal cavity and
from there to the lungs, like our own ears? If so - could they "hold
their breath" for a short while and sense the air escaping or rushing
in to their lungs through any orifice in the ear? Even without a hole
in their ear, maybe they can sense the increasing or decreasing
pressure on their eardrums (much like we can feal air pressure when we
"pump" our ears)? I would think the lung capacity is much larger than
the total volume of the bone "hollows".
I guess more information on bird anatomy is needed here.

Uri - 4XGJC

Jim Skydell wrote in message ...
It's a well known fact that birds bones are very light and filled with
holes, just like we have sinuses in our head bones. I've pondered how birds
might sense rate of climb many times and I now hold the view that they sense
it via the cavities in their bones - this would provide them with a very
sensitive variometer, the capacity being automatically incorporated so to
speak.

Some work was done in the early 70's on this. Whatever a bird's "vario" is, it resides in
their ear. Cutting the 8th cranial nerves (which connect the ear to the brain)
extinguished their ability to sense altitude. This work was done in pigeons, (not soaring
birds, who would be expected to have an even better "vario"). Further work (done in a
pressure chamber) indicated that even a pigeon can sense an ambient pressure change
equivalent to climbing 2 feet.

I'm also convinced that birds soar for pleasure as well as because they
might have to (e.g. Pelicans soar when they are migrating and follow similar
climb/glide patterns to us).

Other research done in the 70's was carried out by a glider pilot in Africa. He wanted to
figure out where all the buzzards went during the middle of the afternoon (all would
disappear every day). They thermaled up, out of sight from the ground. Either for
pleasure,or to cool off?

On 4 Jul 2004 14:20:05 GMT, Derrick Steed
wrote:

I once observed a seagull from the restaurant at the top of the OMPI
building in Geneva - a seagull was already soaring near the ITU building
when suddenly another shot past the window in a fast glide headed straight
for a point below the other seagull, when it got there it pulled up into the
climb underneath the other gull turning in the same direction. Obviously
his/her CSI (Chief Seagull Instructor) had made the point about proper
thermal entry.

I've noticed that gulls joining a thermal will almost always circle
the same way as the birds or gliders already in it. I've had them join
me when I was the sole occupant of the thermal and they have always
respected my turn direction. I wish I could say the same about the
small raptors around Cambridgeshire - they often join going the wrong
way and keep a pretty poor lookout too.

Judging from what I've seen from the ground kites and vultures have
better thermalling manners than their smaller relatives. That said,
back in the late '70s I remember seeing a stationary thermal in Jaipur
over the local abattoir that was stuffed with several hundred Indian
vultures. They were flapping up to join at 100 ft or so and riding it
to at least 1000 ft before peeling off in a skein that crossed the
city to another thermal - a magical sight. I wasn't a glider pilot
then, but I remember that a few were turning the wrong way. Sadly, I'm
told that this sight has now vanished from Indian skies. 95% of the
vultures have been killed by a now-common veterinary medicine and the
farmers are learning the hard way just how much cleaning up the
vultures did for them.

--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

Pardon this input from an uninformed intruder to this subject, but why couldn't
birds simply sense how strong the lift is by the amount of stress it puts on
their "airframe". When I pump iron, I'm all too aware of the amount of effort
required. Surely birds can do the same.

Ted Frost
Soaring Society of Boulder

On 04 Jul 2004 18:48:04 GMT, ospam (Frostowits)
wrote:

Pardon this input from an uninformed intruder to this subject, but why couldn't
birds simply sense how strong the lift is by the amount of stress it puts on
their "airframe". When I pump iron, I'm all too aware of the amount of effort
required. Surely birds can do the same.

Some seem to do just that. Kites in particular. I used to watch them a
lot in India and discovered that you can tell how strong the lift is
by looking at them - the stronger it is the more dihedral they use. If
its really strong they just bomb round with a steep V-form and their
tip feathers closed. Weaker lift gets more care and attention, less
dihedral and more open tip feathers. When they're really scratching
their wings are flat or even a little anhedralled and the tip feathers
are fully spread and up to give tip dihedral. They initiate a turn
with a big dab of negative in the inner tip and then control the turn
on tail tilt - the outer tail tip is raised, so you can tell that
they fly like we do with down force on the tail. Kites are easy to
read because they often work low altitude lift where you can see
exactly what they are doing and have big, long tails that are easy to
observe.

I wondered about how vultures fly but they were so seldom low enough
to really watch that I couldn't work out very much. Also, with much
shorter tails than kites its difficult to see whether they use tail
tilt at all or which way its applied.

The above is about all I know about soaring birds: I'm no
ornithologist or naturalist. My background is chemistry, competitive
free flight model flying and, latterly, soaring.

I've heard a number of theories about how birds detect thermals
including that they hear them. I'd well believe that, with a nerve on
each feather, they must *really* feel the air and all its
micro-turbulence. Maybe they can hear it too. However, that tells
something about how they work 'normal' thermals but not a lot about
how they can find and work the very weak, smooth lift you get early
and late in the day. We know that migratory birds have a excellent
directional sense so why shouldn't a soaring bird have a built-in
vario too? I'd love to know how it works.

If you haven't read it, find a copy of Philip Wills' "On Being A
Bird". There's a chapter about flying with vultures in South Africa
and how he worked just how vultures operate - altitudes, spacing, food
finding strategy etc. The whole book is a good read too.

--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :