h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I have noticed that birds flying against a light background (sky) appear dark but against a dark background (the surface of the planet) they appear light (seagulls for instance and most noticeably). I assume it is brain interpretation as with the recent yellow dress, blue dress that grabbed the internet's attention but does anyone know how it works or what the explanation for it is?

I think it's more like the eye being like a camera...

If the sky is bright behind an object eg a gull, then the amount of light reflected off the gull is relatively small in comparison with the light entering the eye from the sky, causing the gull to seem dark.

Against a dark background, the amount of light reflected off the gull is comparatively more so it appears brighter to the eye.

That sounds reasonable.

perhaps the gull was gray or offwhite anyway,making ti darker than the light sky, and lighter than the ark sky.

Something akin to that gull, frequently reported in UFO journals, what appears to be a mirror-bright peanut, flying at 45 degrees to its long axis, usually reported due east or due west early in the morning, just before sunrise or late in the afternoon immediately after sunset, in point of fact a pair of birds flying close together, illuminated by the sun from below, in the same ultramicroscope effect that makes the moon appear white even though its almost charcoal black.

With flights of birds the effect is most dramatic with large flocks flying in V-formation.

~ WOW ~ . .. ... . .. ...

Interesting captain!

If it's in the sky, you cant blame the squirrels, hampsters, or mice.
That just leaves birds, who are apparently eager to oblige.

SashaQ, I think you are right. Yesterday down the river, a shaft of light came through the trees and I noticed (as I have before but never made the connection) that suddenly everything seemed darker than it was before as my iris closed to shut out the light. Therefore it is not the birds that appear darker or lighter but it is about the eye shutting out or letting in more light! I feel like Hercule Poirot as played by David Suchet "What an imbecile I have been Hastings! The answer has been in front of me all the time!"

Imbecilic moments come to all of us.

And thankfully go...

Well yes, that too.