Re: Altitude effects on hummingbird flight?

[jrc <jrccea@bellsouth.net>]

----- Original Message ----- 
From: "don ohmes" <d_ohmes@yahoo.com>
To: <dinosaur@usc.edu>
Sent: Thursday, December 21, 2006 10:44 AM
Subject: Re: Altitude effects on hummingbird flight?


> No, a number of other, much larger birds use hovering -- but they do it by
> means of a different technique, full alternating momentum reversal (the 
> flutter stroke).
> You will see hawks doing it regularly while hunting, and they are for the
> most part, larger than hummingbirds.
>
> ------------- Not as a primary form of locomotion, they don't.

No, of course not.  They use it for hovering, not locomotion.  The same is 
true of hummingbirds and those bats that hover.

> Especially in still air.

Umh, what does still air have to do with it?

> If you define "hovering" as "remaining stationary relative to the ground", 
> yeah, lots of stuff "hovers",

I don't know of anyone who defines that as hovering.  Do you?  Hovering is 
remaining stationary relative to the ground in still, uniform air.

> especially in moving air.

Again, what does moving air, per se, have to do with it?  As you know, for 
animals in flight to extract energy from the atmosphere, there has to be 
shear, turbulence, or some form of updraft present.  A uniform wind has no 
effect  whatever on the physics of flight,  except  for the special case 
where some part of the animal's body is in direct physical contact with a 
second medium of differing density.

> Perhaps I should have said, "largest observed species using hovering as a 
> primary form of locomotion...",

I don't interpret hovering as a form of locomotion (with locomotion being a 
means of translating through space).  However, accepting your definition for 
the moment.  The largest hummingbirds weigh about 19-20 grams.  The largest 
bats that hover (for durations similar to hummingbirds) weigh about 30-32 
grams.  The largest birds that hover for similar durations by means of full 
alternating momentum reversal weigh hundred to perhaps  thousands of grams. 
I've not checked to see which is the largest bird known to make use of the 
technique, but they are quite big relative to hummingbirds and most bats.

> but as I was discussing evolutionary scenarios, I didn't think it 
> necessary. IIRC, Pennycuick says pigeons are about maximal for "hovering" 
> in _still air_, and that is momentary (less than 4 min), not primary.

Umh, even in hummingbirds, most hovering is for durations of a few seconds 
only.  Fifteen seconds is a pretty long time even for hummingbirds.  Pigeons 
are pretty good sized.  And, I suspect that Colin's definition of  'still' 
air may be somewhat different from yours.  As an aside, Colin's knowledge of 
vertebrate flight is truly extraordinary.  He has my utmost admiration.

> Unless it is a functional bottleneck relative to ecology, it seems 
> unlikely to control flight morphs...

I've lost track.  What does "it" refer to in the sentence above?

> ------------ No functional equivalence, no convergence. Not a primary form 
> of locomotion, no equivalence. The African species sounds interesting. On 
> my list of things to do.

I believe you and I may also have a slightly different definition for the 
term "locomotion".  I define it as "The act of moving from place to place. 
The ability to move from place to place".  How do you define it?

> ------------- It all seems downright weird to me.

Yeah.  All of life is truly weird.  Which is what makes it so fascinating.

JimC