Hummingbird Feeders. Hummingbirds get the energy they need to maintain their astonishing metabolism primarily from flower nectar and the sugar water they find at feeders (here's the recipe). Think of them as miniature flycatchers, and sugar is just the fuel for getting their real nourishment.
afÂ·terÂ·imÂ·age. n. A visual image that persists after the visual stimulus causing it has ceased to act. Also called photogene. (ËÉËftÉrËÉªmÉªdÊ).
Vision is a combination of distinct measurable functions: visual acuity, color vision, vernier (alignment) acuity, the perception of movement and change in luminous intensity (flicker) or differences in luminous intensity (contrast). Visual acuity is the ability to determine fine detail and distinguish one object from another. Acuity is tested with vision charts of letters or images. Changes in luminous intensity are perceived as flicker, and the difference in luminous intensity from one object to another is perceived as contrast [1]. The visual field encompasses the entire region of space seen while gaze is directed at any central object.