On Mon, 22 Jan 1996 11:11:13 -0800 (PST), Christopher Hill wrote:

> On Mon, 22 Jan 1996, Herb Curl wrote:
> >
> > Jim Russo has been favoring us with an essay on owl vision. What I've
> > missed so far is a statement concerning their alleged ability to see light
> > in the near infrared, and thus locate warm prey that would appear lighter
> > than the cooler background.

> No evidence to suggest that owls can see in the infrared (IR). The
> following behavioral experiment indicated that in darkness it is sound
> rather than IR vision that is used:

> Payne, R (1971) Acoustic location of prey by barn owls (_Tyto alba_).
> Journal of Experimental Biology 54:535-573.

> Payne put a barn owl in a completely dark room with a mouse. The barn owl
> was able to catch the mouse. Then, to test whether the owl was using
> infrared or sound cues, he attached a small piece of paper to a string
> attached to the tail of the mouse. The owl now struck at the paper (which
> rustled louder than the mouse feet) rather than the the mouse.

I may be splitting hairs here but I suspect the test performed by R. Payne
in 1971 gave the owl little chance of catching the mouse. By putting the
owl in a dark room there was no IR by which the owl could see. It seems to
me that Mr Payne was testing the owls ability to detect heat which is at a
longer wave length than near IR. I would suspect a more proper test would be
to provide illumination by an IR source (only) then intruduce a masking
noise to confuse the owls ability to hear. If the owl is then able to catch
the mouse I would have to suspect the bird could see in the near IR.

Does anybody know what the ambiant IR would be in the great out of doors
under different sky conditions? I suspect there would be little IR at night
even under a full moon. I further suspect that if there were enough IR for
a bird to see there also would be a relatively high level of "visual" light
such that the birds would not need the IR at all.

Doug Hudson
Bremerton,WA
dhudson at linknet.kitsap.lib.wa.us