It is nice to see that you are aware of, and making the birding community aware of the problems with color perception. I have been studying birds and color perception for some time and am amazed that this is not an issue in the natural history community (although I may be unaware papers and such). There are many references to the problem in the art world, Josef Albers “Interaction of Color” shows just how tricky judging color can be. Betty Edward’s book “Color a course in mastering the art of mixing color” is worth reading even for non-painters. In one chapter Edwards relates a story by a fellow painting teacher who set up a still life with white geometric objects and some eggs. The still life was illuminated with only a pink spotlight. The students painted the geometric shapes in pink tones but painted the eggs white because they “knew” eggs were white. This illustrates something of a problem that can be encountered when seeing birds in the field. It is possible to mentally paint birds the colors we think they should be, which is fine for birds we know well, however it may be a problem for a bird that are for some reason ambiguous. This may be something of a psychological issue, but there are many physiological reasons that our color perception may be less than “true” Margaret Livingstone’s book “Vision and Art, The Biology of Seeing” shows that in the process of seeing images are highly “filtered” as they change from photons to something we perceive as an image in the brain. The book has an excellent example of the Cornsweet Illusion which shows how difficult it is to perceive gray tones. I applaud Steve Howl’s use of the Gray Scale in identifying gulls, however understanding the Cornsweet Illusion we see that the use of a Gray Scale in the field also has its pitfalls. Color and visual perception are events that we as individuals are constantly interpreting and they are not as solid and “real” as we are led to believe.

In my opinion there is no evidence here of melanism at all. I have quite a bit of photofinishing experience having worked in that industry for many years. While it is not possible to totally reverse the effects of under-exposure there is additional information to be gleaned from such images when appropriate photofinishing corrections are made and I think an attempt should always be made to try and correct colour and density errors created by improper camera exposure. While it may be very difficult, particularly for the untrained eye to find a photographs “Normal” exposure its always worth a try.

I find the images presented here to be cold (too much blue, cyan and green) and dark. When one corrects for the cold colour cast and excessive density in the images presented what is revealed (at least to my eyes) are two perfectly normal looking Swainson’s Thrushes.

That aside, your remarks about colour illusions are very interesting indeed. I am always fascinated by how variable some Old World Acrocephalus and Hippolais warblers can look during the autumn depending on the type of foliage they are moving through and whether they are in shade or in the open. It makes the task of accurately describing and also accurately photographing these birds next to impossible at times.

Regards

Michael O’Keeffe
Ireland

I known that it’s impossible to have exactly the same kind of shadow in both birds (variable shadows under a tree) but it give a idea.

My two cent
Marcelo Brongo
Barcelona, Spain