Taken From - "The Great Cover-Up"
Summary: Who has not wondered why a flock of ducks or geese flared from a blind or pit at the last minute? You know, when you were hunkered down, gun in hand, waiting for what seemed at the time to be the birds' bank into their final pass. All of a sudden, however, just when it appeared they were headed in, they veered on way or another and departed to points unknown. What turned them off? Or what turned them on to your location? What gave you away?
Taken From - "Yes, Ducks Really Can See Things We Can't"
"Can ducks really see things we can't? Yes, they can. But this comes as no surprise to those of us who spend significant amounts of time trying to get closer to them (or getting them to come closer to us). Certainly, the entire explanation for such excellent eyesight is not completely known, but scientists have found out quite a lot.
Birds in general have relatively large eyes that make up a greater percentage of total head weight than most mammals' eyes. Size, however, is just the beginning of the difference. Inside the eye we find a complex retina. The retina is the back portion of the eye that receives the light that has passed through the lens. For most diurnal birds (those active during daylight hours), the retina is packed with adaptations for enhanced vision. Birds possess up to five times greater concentration of cone cells (color receptors) than humans.
It is logical, then, that nocturnal birds such as owls possess fewer cone cells, in favor of more rod cone cells (those that detect dark/light). The cone cells of diurnal birds are further associated with colored oil droplets, thus allowing greater range of color discernment. As an illustration, imagine your world colored with a 24-color box of Crayons, while a bird's is colored with a box of 64.
When you think about it, there are an infinite number of possible colors of different shades and hues. Birds simply can detect a greater percentage of those (even near-ultraviolet), owing to the attributes of the cone cells. The retina of a bird's eye also has a deep concave depression - filled with cone cells - that may aid in the detection of movement of small images (including those far away). Remaining still while in the blind or pit is key to remaining undetected.
When you couple a duck's enhanced vision, its ability to learn, and natural selection working against hunters that do not put these to good use, its not so difficult to understand why camouflage and concealment are integral parts of a waterfowler's tool kit."
Based upon the information provided above, it's very easy to see why concealment is such a vital factor to your overall waterfowl hunting success.
In addition, the information blows away a commonly held myth that ducks and geese are colorblind and only see in shades of black and white. As you can see, nothing could be farther from the truth. Also, their keen eyesight and their ability to learn and adapt only gives additional proof to the fact that both ducks and geese can detect and will often avoid objects (i.e. blinds) that do not fit in to and match the natural surroundings.