Why Lighting Conditions Can Throw Birdwatchers A Curveball

One of the main cues we use to identify birds is color, and the color we perceive is entirely dependent on lighting. The challenge of color perception is not limited to bird identification, of course, and we are constantly making (mostly unconscious) adjustments to determine the color of things we see around us. Bird identification simply brings this challenge to the fore.

Most of the time, we do a good job of adapting to the lighting conditions, and can recognize a color, for example, the particular shade of yellow in a male American goldfinch, whether the bird is in direct sunlight, or deep shade, or the warm glow of sunset. We can do this because we judge colors by the colors around them, and the general lighting in a scene tells us what to expect. It may take a while to “recalibrate” our color perception, but once we have adapted to current conditions, we may see a goldfinch and say, “ah, yes, the typical yellow color.”

Occasionally, however, the lighting throws a curve. In some cases, we misinterpret the scene – our color grading is off. In other cases, there’s just a small variation we didn’t expect – a greenish glow reflecting off a leaf or an unexpected shadow, for example. Something like this happened to me recently while watching terns in Long Island Sound, New York.

It was early morning and I was looking south over the water. Dozens of Common Terns were flying, moving mainly west (left to right). They were brilliantly lit by the morning sun. Suddenly, a very black tern appeared among the groups of passers-by; “Black tern! I thought. A few moments of study revealed that it was just another Common Tern, in the shadows. But how could it be in the shade, in full sun above open water?

With the sun directly to my left, any birds traveling in a slightly slanted line toward me were illuminated by the early morning sunlight. But when a bird deviated from that line of flight and flew slightly away from me, the sun hit the far side of its body instead, leaving me with a view of dark shadows on the near side of the bird. ‘bird.