Positioned between brain and beak, a bird's eyes guide it's every movement and meal. These eyes differ in size, placement, and anatomy according to the lifestyle adaptations of each species.
Birds also have colored oils in their light receptors that filter out certain wavelengths to sharpen others. The proportions vary from species to species to give particular advantages. Just as the yellow tint of aviator sunglasses sharpens clouds against a blue sky, a warbler benefits from red filters to enhance differentiation among greens.
Light bending at the water surface confuses our eyes on the precise location of objects underneath. Egrets are able to correct for refraction. Their strikes are most successful when made at an acute angle, where they seem to be less detectable to fish.
Birds that hunt on the wing tend to have retinas highly enriched with cone sensors, several times that of humans. They can process images more quickly than we do into a series of discreet sights that to us may appear as an undifferentiated picture, like seeing individual film frames in slow motion.
|Pigeon skull (2)|
To save space for optical developments birds have given up the muscles that allow us to move our eyes from side to side or up and down. Neck muscles move their whole head instead. As food gulpers rather than chewers they streamline their skulls without teeth and large jaw muscles.
This hunter's posture is all purpose and focus, leaning into the prospect of taking a life to carry on its own. The full force of its intent lies poised behind the eye in a chilling acknowledgement of survival equations. The eye reveals the bird's nature as acutely as it guides its actions.
(1) Physiology resources: Wikipedia article "Bird Vision"; and the website "How Birds See their World" by Dr. Esteban Fernandez-Juricic, Purdue University
(2) Image from Skullsunlimited.com