Circling for rodents?

Martin Gregorie wrote:
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.

Well, the stress only occurs briefly on entry into the thermal,
when you have upward acceleration. Once established in the climb,
assuming it is more or less smooth, you no longer have acceleration
nor any acceleration generated stress forces so you need some other
means of knowing whether you are still climbing, such as rate of
pressure change, which is what the vario measures.

cheers CV

assuming it is more or less smooth, you no longer have acceleration
nor any acceleration generated stress forces so you need some other
means of knowing whether you are still climbing, such as rate of
pressure change, which is what the vario measures

If the rate of climb is not changing, then there is no acceleration. If the
climb rate reduces, than there will be an acceleration in the negative (down)
direction. The rate of change of velocity is the acceleration:
dV/dt=acceleration.

Jim Vincent
N483SZ
illspam

It's pretty well established that soaring birds have extremely good
eyesight. I think they just see the ground moving away when they are
climbing. Thermals also have a lot of stuff in them like insects and seeds.
The birds are probably able to see these rising at a considerable distance

There's a lot of visual cues while thermalling. If you are trying to thermal
near a mountain peak it's easy to see the glider rise at the onset of lift.
The varios will signal lift two or three seconds later.

BTW, that story about the USA hang glider team chasing buzzards and landing
next to a dead cow is really funny.

Bill Daniels



"Derrick Steed" 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.

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).

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.

Rgds,

Derrick Steed
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

(Andy Durbin) wrote
in
message
news:...
"Bill Daniels" wrote in message news:...

Most hawks circling low are looking for rodents, not lift.

Bill Daniels


But many times I have shared thermals with Hawks at high altitude.
How did they get there if not by working thermals at low altitude? I
have never been in a thermal with a Red Tailed Hawk that didn't seem
to be trying to optimize climb rate. Turkey Vultures are a different
story. They seem to be happy with any sloppy thermal technique as
long as they maintain altitude.


Andy

CV wrote:

Well, the stress only occurs briefly on entry into the thermal,
when you have upward acceleration. Once established in the climb,
assuming it is more or less smooth, you no longer have acceleration
nor any acceleration generated stress forces so you need some other
means of knowing whether you are still climbing, such as rate of
pressure change, which is what the vario measures.

Why wouldn't they just _see_ that they are getting higher? The vast
majority of birds operate at altitudes where looking at the ground tells
ME whether I'm climbing or descending accurately enough for all
practical purposes and birds have far better vision than I do. Altitude
measurement by eye would be fine without ATC radar second-guessing you.

I think Martin is probably correct. Humans have a very sensitive g
meter in our leg and body muscles. I suspect that birds have even better
ones in their wing root muscles ('proprio-sensors' from a hazy Biology
101). I would have thought inbuilt stress gauges combined with accurate
vision provided a perfectly possible and very probable set of flight
sensors. Birds probably also have a built in AoA sensor in the tail
muscles which gives control load feedback. AoA may also come from
feedback from feather control muscles, especiallly the pinions. I'd
guess these are integrated with the g sensors.

The visual bit for altitude is quite secondary, I'd guess. Steady state
lift is a theoretical concept, not reality. Lift is constantly varying
and a sensitive stress gauge would always be detecting some change.

When it comes to birds, you have to start with the idea that their
flight system is probably more fundamental than our balance and walking.
I suspect that a bird's flight control system is completely integrated
at a quite deep level. I would guess that the muscle movements to
centre lift are almost directly connected to the muscle feedback that
detects a decrease or increase in lift - and that feedback probably
comes from several different sources.

I think the birds fly like us. By the seat of their pants, visually.

cheers, GC

cheers CV

On Wed, 07 Jul 2004 23:03:26 +1000, Graeme Cant
wrote:

When it comes to birds, you have to start with the idea that their
flight system is probably more fundamental than our balance and walking.
I suspect that a bird's flight control system is completely integrated
at a quite deep level. I would guess that the muscle movements to
centre lift are almost directly connected to the muscle feedback that
detects a decrease or increase in lift - and that feedback probably
comes from several different sources.

That's certainly true. We have to learn to stand up and walk as babies
while a colt, for instance, can stand and walk within minutes of
birth. A bird can fly well enough to gain height and steer once it has
fledged and its muscles are developed, so that puts its flight system
closer to a horse's ability to walk than to ours, i.e. at a more
instinctive level.

I'm not saying that they don't learn to fly better or that all birds
are created equal - you only have to watch a flock of gulls soaring a
cliff in light conditions to see that some birds fly much better than
others.

I think the birds fly like us. By the seat of their pants, visually.

Agreed. I just can't imagine having all the information they must get
while flying just flowing in from every nerve. I think I'm envious.

On raptor vision and the story about buzzards climbing to cloud base:
I find it hard to believe that's hunting behaviour and subscribe to
the mating display and/or joy of flight theories:

- I saw an eagle travelling xc in Hungary last year. It went to cloud
base under one cloud and set off dead straight so it was obvious where
it thought it would get its next climb half-way there it evidently ran
into lift and, just like we would, thought "This is good - lets have a
circle". It looked to be a lumpy, multi-cored patch patch and it
evidently really got into finding the strongest bit before really
tightening up and coring it. Doubtless it was thinking "Yes! Got it!"
as it climbed. It eventually left on its original course. I'd rate
this as soaring for fun: the bird was very high to start with and just
plain didn't need the climb.

- Philip Wills observation that the African vultures didn't hunt above
2500 AGL and that they were spaced about a half mile apart (both
distances are the same for metric speakers), so this marked about the
limit of fully acute vision for vultures makes a lot of sense to me.
I'd expect the same to apply to eagles, etc and suspect that the their
acute vision limit is a lot less than 5000 ft cloud base of the story.
Needless to say, they can't hunt from above cloud base in a Cu!
Kestrels hover preferentially at 50-100 feet and when I've seen
harriers and buzzards hunting they've usually been under 500 ft.


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

Bill Daniels wrote:
It's pretty well established that soaring birds have extremely good
eyesight. I think they just see the ground moving away when they are
climbing.

Good eyesight is one thing, precision at judging distance another,
the latter basically dependent on how far apart your eyes are.

No way can they judge their climb rate based on seeing the ground
moving away.

Thermals also have a lot of stuff in them like insects and seeds.
The birds are probably able to see these rising at a considerable distance

That could be, and other visual cues as well.

CV

C'mon, now. Binocular depth perception ends for humans at about 20 feet and
is only really useful up to arms length, yet we can still judge distance
well. Since the bird is moving, they can use dynamic field depth perception
that has nothing to do with interocular distance.

Close one eye and move your head back and forth or up and down. You will
see what I mean. Birds and other small animals are observed to move their
heads constantly to better judge distances.

Ever ride one of those glass elevators (lifts) on the outside of a tall
building? Did you notice how powerful the impression of climbing is?

I still claim that they can see themselves rise away from the ground.
Excellent vision and the experience to use it to the fullest is the likely
explanation. It's the simplest explanation and requires no internal vario.

Bill Daniels


"CV" wrote in message
news
Bill Daniels wrote:
It's pretty well established that soaring birds have extremely good
eyesight. I think they just see the ground moving away when they are
climbing.

Good eyesight is one thing, precision at judging distance another,
the latter basically dependent on how far apart your eyes are.

No way can they judge their climb rate based on seeing the ground
moving away.

Thermals also have a lot of stuff in them like insects and seeds.
The birds are probably able to see these rising at a considerable
distance

That could be, and other visual cues as well.

CV

Graeme Cant wrote:
majority of birds operate at altitudes where looking at the ground tells
ME whether I'm climbing or descending accurately enough for all
practical purposes

Well, supposing you are flying at 1000 ft and hit a 2 knot
thermal. The distance to the ground would be changing at a
rate of 0,3 per cent per second. It is a little hard to
believe that anyone can detect that by eyesight alone.

Sure, after a while you'll be able to tell you are higher,
when everything is smaller, but that's not quick enough
to help you stay in the thermal.

CV

Jim Vincent wrote:

assuming it is more or less smooth, you no longer have acceleration
nor any acceleration generated stress forces so you need some other
means of knowing whether you are still climbing, such as rate of
pressure change, which is what the vario measures

If the rate of climb is not changing, then there is no acceleration. If the
climb rate reduces, than there will be an acceleration in the negative (down)
direction. The rate of change of velocity is the acceleration:
dV/dt=acceleration.

That is not much use to us humans though. We have very poor
ability to "integrate" the sense of acceleration over time,
which is very convincingly demonstrated by how quickly we
become disoriented in IMC.

If birds happened to have a higher developed sense for this
than humans, then that could be part of the explanation but
I wouldn't bet on it.

CV

Come on you lot! cant you remember your first flights in gliders without
elec varios? birds do what we all did in the 70s listen, you always hear the
rush close to the centres