Re: Flying Along a Logarithmic Spiral

[brian whatcott <inet@INTELLISYS.NET>]

At 14:52 12/20/00 +0100, Bill Larson reported:

> Flying Along a Logarithmic Spiral
>
> Peregrine falcons use two high performance skills - flight speed and visual
> acuity - to attack their prey. In a trio of papers, Tucker and his
> colleagues model the quantitative aspects of aerodynamic drag, assess the
> optimal integration of speed and sight, and present field observations of
> falcon flight. Drag, particularly at flight speeds in excess of 50 meters
> per second, is minimized by keeping the head aligned with the body, but this
> presents a problem: prey of the size of a robin can be seen from a distance
> of 1 km only by using the deep fovea, which is oriented at an angle of about
> 40 degrees from the head axis.
/snip/

> J. Exp. WoL 203,3733; 3745; 3755 (2000).
>
> from www.sciencemag.org SCIENCE VOL290 8 DECEMBER 2000
> Dr. William J. Larson
> Bill_Larson@csi.com
> Institut Monte Rosa
> Montreux, Switzerland


Bill's abstract is of general interest. It has enough data to estimate
the visual acuity of the Peregrine (a 5cm ? robin at 2 km.?).

  It begs some more speculative questions: "if evolutionary design
efficiencies are so darned effective at optimizing a design, why
isn't the direction for maximal acuity situated straight-ahead anyway?"
 - for example. The general design layout for the bird has been around
 an exceptionally long time - and even a novel construct like the mammal
 can fine focus nearly straight ahead, can't it?

 This suggests there are competing objectives involved - indeed Bill
mentions head streamlining versus light gathering (where the Owl seems
to have been optimized for rather different visual/flight conditions
as an airborne predator.)  I expect that birds in general have the
built in capability of "keeping your head on a swivel!"
 - the advice given to novice pilots... by its panoramic view which is
not apparently optimized for binocular fusion and depth perception by
this means.
 Recalling the continual tremor without which the human eye rapidly
grays out, it could be that a helical scan offers pattern recognition
virtues too. (I should also finally mention that it is generally conceded
that evolution is not considered a perfect mechanism - but good enough;
that is, until your appendix starts aching interminably, for example.)

Brian



brian whatcott <inet@intellisys.net>  Altus OK
                Eureka!