Circling for rodents?

In article , Uri Saovray
writes
Does anyone have an idea of how the birds know where to thermal? Do
they have a vario? Where is it? Where is its capacity?
Assuming they breath while thermalling, then I doubt they use their
lungs as capacity... or maybe they stop and sense the air coming out
their noses.
Just wondering...

Uri 4XGJC

Its a long time since I did any comparative anatomy, but I believe many
birds have air filled cavities in some of their bones.

While on the subject of birds using thermals, the German expedition to
the Andes (1937) decided to bring some raptors birds back to Germany,
the idea being they would find thermals for them. During the voyage back
they were of course kept in cages and fed by the crew. And everyone
else.

When the ship docked in Bremen, the birds had got so heavy they couldn't
get airborne.

From a biography of Hanna Reich.
--
Mike Lindsay

Can birds sense pressure changes? Maybe they have bio-varios.
I've noticed they seem to chirp, even on gloomy mornings,
when I have noticed pressure rising on the
altimeter or baro. It wouldn't surprise me if
this was true, but I haven't heard of any studies...

So I'm guessing maybe they know they are
climbing from vario alone...

In article ,
Derrick Steed 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.

Ted Frost
Soaring Society of Boulder

The stress would only change when acceleration was present (as in entering a
thermal, we use our bums for for that - transitting from an area of intense
sink to and area of lesser sink: e.g. no thermal). In a steady climb the
stress wouldn't change and would be the same as in normal turning flight. I
suspect that Martin's observation about the birds choosing a more extreme
dihedral has more to do with lack of effort than sensing the lift intensity
- a high dihedral result and a high value of lateral stability, but poor
efficiency of the wing.

Rgds,

Derrick Steed






--

------------+
Mark Boyd
Avenal, California, USA

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?

Uri Saovray wrote:
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 ...

But you CAN fool an accelerometer in a uniformly ascending mass of air, but
not a vario...

Rgds,

Derrick Steed

Hi,

But you CAN fool an accelerometer in a uniformly ascending mass of air, but
not a vario...

How? You have to enter that mass of air at some point and there you
will record the acceleration.

Ciao, MM
--
Marian Aldenhövel, Rosenhain 23, 53123 Bonn.
Fon +49 228 624013, Fax +49 228 624031.
http://www.marian-aldenhoevel.de
"Wie trennt man drei Schlampen von zwei Säufern? Cockpittüre zu!"

Derrick Steed wrote in message ...
Uri Saovray wrote:
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 ...

But you CAN fool an accelerometer in a uniformly ascending mass of air, but
not a vario...

Rgds,

Derrick Steed

I have just started to read this thread and became interested in the
various theories on how birds sense thermals. I would like to quote
from Phillip Wills well known book "On Being A Bird" where he contends
that soaring birds hear thermals. He goes on to say that "the birds
ear drum is anchored from the opposite side (from that of man) so is
streched by decreasing pressure, thus in all likehood giving him a
sensation when he climbs." For those interested this is from page 29
Paragraph 3. If you haven't read this book, shame on you!

Lorry Charchian (LJ)

Rgds,
I did say "uniformly ascending mass of air", I didn't say how one got there. For the given condition it's just a statement of Newton's first law.

If you've done any relativity, you'll know that the twins paradox in special relativity suffers from the same problem.

Derrick Steed
Hi,

But you CAN fool an accelerometer in a uniformly ascending mass of air, but
not a vario...

How? You have to enter that mass of air at some point and there you
will record the acceleration.

Ciao, MM
--
Marian Aldenhövel, Rosenhain 23, 53123 Bonn.
Fon +49 228 624013, Fax +49 228 624031.
http://www.marian-aldenhoevel.de http://www.marian-aldenhoevel.de
"Wie trennt man drei Schlampen von zwei Säufern? Cockpittüre zu!"

Bob writes
impossible for them. (Anyone know the maximum all up
weight of a swallow)

Would that be an African or European swallow?

Albatross! Get your fresh albatross here!

Hmm... Perhaps it's too early in the morning for such abstract,
serpentine humour :P

Hi,

I did say "uniformly ascending mass of air", I didn't say how one got there.

All right. If you put an accelerometer in an ascending mass of air and
then, when it moves with that mass of air, read it, it will show zero.
I concede that :-).

But that is the same thing as saying a vario will read zero when the
pressure around it is not changing.

I cannot quite understand how that relates to "fooling" an
accelerometer. There is no way to get it from lying on the ground
to moving with the uniformly ascending mass of air without it showing
a non-zero value at some point in time.

So, if birds can be made to believe that they are changing altitude by
putting them in a pressure chamber and changing ambient pressure, then
I think accelerometers as sensors are indeed ruled out. At least as
singular source of input.

In these experiments how does one know that the bird thinks it is
climbing or descending? If you put a human into the same chamber it
will likely notice a change in pressure, even if not as small a
change as the bird. But we are rarely able to tell which way, much
less relate the relative change in pressure to absolute change in
altitude.

Designing an experiment where one can make sure the bird translates
pressure change to altitude seems hard to me.

Ciao, MM
--
Marian Aldenhövel, Rosenhain 23, 53123 Bonn.
Fon +49 228 624013, Fax +49 228 624031.
http://www.marian-aldenhoevel.de
"Wie trennt man drei Schlampen von zwei Säufern? Cockpittüre zu!"

At 09:36 06 July 2004, Marian_Aldenhövel wrote: (snip)

will likely notice a change in pressure, even if not
as small a
change as the bird. But we are rarely able to tell
which way, much
less relate the relative change in pressure to absolute
change in
altitude.

We can detect which way the pressure is changing but
the rate of change has to be large for us to do it.
( Hold nose on way down and blow to push the eardrum
out as pressure increases and hold nose and swallow
when climbing, and before someone says that is not
a good thing to do I know. Birds appear much more sensitive
to the change in pressure.

Designing an experiment where one can make sure the
bird translates
pressure change to altitude seems hard to me.

I don't think anyone was saying that birds use the
pressure change to measure altitude, as an altimeter,
but they do appear to use it as we do a vario. I don't
think birds worry whether they are at the correct flight
level or above transition altitude even. A vario works
by measuring small changes in air pressure.

Ciao, MM
--
Marian Aldenhövel, Rosenhain 23, 53123 Bonn.
Fon +49 228 624013, Fax +49 228 624031.
http://www.marian-aldenhoevel.de
'Wie trennt man drei Schlampen von zwei Säufern? Cockpittüre
zu!'