> From: Dave Land <[EMAIL PROTECTED]> > > On Aug 10, 2004, at 3:33 PM, Travis Edmunds wrote: > > > > >> From: "Robert J. Chassell" <[EMAIL PROTECTED]> > >> Date: Sat, 7 Aug 2004 21:25:13 +0000 (UTC) > >> > >> Ronn!Blankenship <[EMAIL PROTECTED]> wrote > >> > >> ... some types of birds have five types of cone cells, suggesting > >> that they can see colors we can't. > >> > >> Can you tell us more? This is deep. > > > > Just asking a question here. Does anyone know or remember which type > > of bird navigates by actually 'looking at' the Earth's magnetic poles? > > Apparently they can actually see something like a red orb which they > > use as a landmark of sorts. > > This <http://www.ks.uiuc.edu/Research/magsense/ms.html> appears to be > the source > of the image showing the "red orb" (the image appeared in the document > labeled > "Graphs and Stuff" in Ronn's "Birds, was Horses" message of a couple of
> days ago. > > I don't think the image was intended to suggest that birds actually see > a red orb, > but to suggest that some kind of visual indication of magnetic > orientation may be > incorporated into avian vision. I was under the impression that certain reptiles had 4 cones, one for infrared. And that mammals who evolved from these reptiles, lost most of their color vision cones because they became nocturnal rodent like burrowing creatures (which is why they survived the massive fireball when a certain meteor hit the earth killing the dinosaurs some 65m years ago). Also as mammals took over and diversified some of them reevolved limited color vision (which is not as good as the reptilian color vision). In fact certain primates only reevolved the cones for red a short while (15m years) ago. Indeed humans have trouble with color blue, as their eyes cannot resolve details in blue (try reading darkblue text on a black background). Evolution doesn't usually make perfect optimizations, it makes good-enough-jerry-rigged-from-existing-parts optimizations. _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
