# How does a vulture know?

M K Bennett pamkb at mail.bris.ac.uk
Fri Jun 10 02:59:57 EST 1994

```Andrew Wagner (afwagner at STUDENTS.WISC.EDU) wrote:

: >PS: Sorry for my English, but with altitude-meter, I mean an apparatus
: >that measures altitude (What's the correct word? My dictionary doesn't
: > know.).
: >
: It's an altimeter.  If I'm wrong, would someone please correct me?

: Andy Wagner

An altimeter shows you height and yes does show if you are going
up and down but it is another dial that us glider pilots use to tell us if
the air mass that we are flying through is going up or down, this is called a
variometer.  It is usually connected to a simple beeping sound system that
beeps quicker if the air is moving up (eg. in a thermal) and makes a farting
noise if the air is going down (sink).  There is a dial that also tells us
at what speed the air is moving up, in the UK where we have sad little
thermals a pretty good one would move up at 4knots (approx 400 feet/min) and
average at just over 2 knots (approx 200 feet/min).  In the states
supposedly you get 6-8 knots and average 4 knots. The reason for having
this sort of dial is to allow you circle in a thermal and gain altitude.

As for how a vulture or other soaring birds do it Ive no idea.  But it
could just be that they dont "spot" thermals as people do by looking for good
clouds and ground features, they may just fly into them and as their
bodies are so light they get lifted quickly and feel the +ve g force on their
bodies (as you would in a lift starting to go up) and start circling in
the thermal and if they fly into sink they feel the -ve g on their bodies
(as you would in a lift starting to go down) and start flapping to get out
of the sink.

Mike

PS if a glider flies into sink it doesnt just fall out of the air as a
previous poster thought it just flies and looses height quicker than it
would in still air.

```