Re: [KENYABIRDSNET] Ducks and herons

Hi Brian,

This is indeed interesting. And yes our eyes can play severe tricks on us - I was with a group at the cliffs in Baringo (around 20 years ago!?), including some eminent birders, when a confidently identified White-faced Scops Owl in an acacia turned out to be a plastic bag!

Your comments raise some interesting issues. Regarding your video stills, by the way, I'm not sure what your conclusion is? I see many changes of angle in flight, but the predominant blue remains, and I would conclude you have filmed a rueppelli.

Structural colours can be deceptive, as we see all the time from sunbirds, but the 'base' colour tends to come through at the 'right' configuration of position and lighting.

In an instance where a number of birds are together in the same light and at more or less the same angle and configuration, and one stands out as clearly different in colour, as with your Naivasha yellow-billed duck and my Karen Club duck, I would tend to conclude that the difference is real.

The discussion will continue!!

All best, JD

On 7 October 2014 17:07, Brian Finch <birdfinch@gmail.com> wrote:

Dear John
It’s a fascinating discussion on the differences as to how our eyes
perceive structural colour as opposed to “real” colour.
I had to wait until it was suggested that the effect of your birds,
was due to change of angle on a structural colour, before replying.
For years I have been seeing the odd rueppelli with the rich blue
speculum amongst our normal green speculum nominate. Officially there
is no conclusive proof that rueppelli has occurred in Kenya.
Your eyes are not playing tricks on you, the colour is being perceived
as real and not just structural or illusory.
A month or so ago, I took a video of a Yellow-billed Duck at Naivasha.
It showed the rueppelli character of attractive blue speculum, and was
associating with nominate green birds.
I wanted to show that the perception of this colour was not due to
angle reflecting off structure, and rueppelli were visiting us
regularly even though it is not acknowledged.
I edged closer to the bird and waited until it got nervous and took
off. It flew past me, I videoed the bird as it covered 120o or so
before alighting again. As I videoed the bird not only was I getting
the angle changing as it flew past me, but also the angle of the wings
changed dramatically with each beat. What more could I want?
Now look at the images attached for the changes from blue to green!
Best for now
Brian