|MadSci Network: Zoology|
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Short Eared Owl
The short eared owl possesses the exceptional vision typical of most owls. Owls have large binocular eyes with powerful lenses and retinas made up of an abundance of rods (Madson 1996). The pupils of an owl's eye can expand to remarkable sizes and thus can collect light even on the darkest night. The lens (and cornea) serve to focus this light on the retina which contains a preponderance of rods in owls. This large number of rods (retinal cells or receptors important in black and white detection) translates into excellent night vision. Short-eared owls, despite their occasional daytime hunting, possess the general blueprint of nocturnal members of the Strigiformes.
The Barn Owl has nearly world-wide distribution,being absent from only the high Latitudes. It has been introduced into some Pacific islands for rat control and is provided nest boxes in Malaysian palm nut groves for the same purpose. While the barn owl is found all over the US, its numbers are particularly high in California and the Southwest. Farmers and ranchers are increasingly attracted to the barn owl's ability to control rodents better than traps,poison,or cats and at no cost. Barn owls in favorable habitats produce large broods once or twice a year. Each young owl as it nears maturity will eat the equivalent of a dozen mice per night if such prey is available. Adult barn owls kill and consume the equivalent of one large rat or gopher per night. The Owl Rehabilitation Research Foundation,Ontario,Canada, reports that barn owls consume twice as much food for their weight as other owls. The Barred Owl is mostly a nocturnal hunter. It preys on small mammals, reptiles, amphibians, crayfish, and some small birds. In fact, this raptor has been known to attack and eat other smaller owls! A very opportunistic hunter, the Barred Owl can sometimes be seen hunting before dark. This typically occurs during the nesting season or on dark and cloudy days.
Great Horned Owl
The most notable physical attributes of the Great Horned Owl are its large size and prominent ear tufts or "horns." A predator that hunts at night, the owl has enormous yellow eyes set in a broad face, a curved beak and claws, and long fluffy feathers. Its coloration tends mainly toward brown or grey-brown, with conspicuous barring. Very dark races occur in British Columbia and Labrador, whereas extreme whiteness is seen in Great Horned Owls from the Northwest Territories and northern sections of the Prairie Provinces. As is the general case with hawks and owls, the female Great Horned Owl is considerably larger than the male, averaging about 2kg to the male's 1-1.5kg, with a wingspan of about 1.2m. The only larger owl is the Snowy Owl, a winter migrant to southern Canada, whose maximum weight approaches 3kg. RODS and CONES are the light-sensitive cells inside the RETINA. They are called photoreceptors. They contain special pigments that are light- sensitive. When these cells detect light coming into the eye, they send a message back to the brain, which, in turn, translates the message into what we see. Rods and cones got their names because of the shape of the cells. There are approximately 125 million RODS in each eye. Most of the rods are in the peripheral, or side, areas of the retina. They are responsible for gross detection of movement, shapes, light and dark. The vision that we obtain from rods is "black and white". They cannot detect color. Color vision and detailed vision come from the CONES. There are about 6.5 million cones in each eye. They are concentrated in the center of the retina. At the retina's very center, the fovea, there are 150,000 cones in every square millimeter. Although the cones provide us with color vision, they are not as light sensitive as the rods. In dim lighting, we rely on our rods for vision. This is one reason why it is hard to tell the color of an object in a darkened area.
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