close-up of an adult Cooper's. The Sharpy has the very large looking eye and browner color behind the eye. The Cooper's shows the capped appearance set off by the paler nape and the grayer color behind the eye. What doesn't show is the square headed look sometimes seen in Cooper's when the crown feathers are more erect. Taken by banders at the Golden Gate Raptor Observatory, Marin Co., CA. These birds begin life with a bright yellow iris, but as the bird grows older the eye changes to light orange, then medium orange, then dark orange, and finally to a deep, dark red. This pattern of color change is so predictable that scientists can determine the bird's approximate age by eye color alone (Rosenfield et al. 1992) Update 2004: The most recent edition of The Wilson Bulletin, in which there is a fascinating paper by Bob Rosenfield and six other researchers about Cooper's Hawk eye color. It states that "Eye color is not a reliable predictor of age in individual male and female Cooper's Hawks." Some individuals acquire darker orange and red eyes much faster than others, and Cooper's Hawks in British Columbia and North Dakota appear to acquire orange or red eyes more frequently and more quickly than Cooper's Hawks in Wisconsin. Females in all three study areas acquired the darker eye colors more slowly than males, and were less likely than males to acquire the deepest red eye color.