They often hunt diurnal raptors when they come across their often relatively conspicuous active platform nests during hunting forays in spring and summer, taking numbers of both nestlings and brooding adults. Peregrine Falcons harass nesting Great Horned Owls. The iris is yellow, except in the amber-eyed South American great horned owl (B. v. nacurutu).  Fledgling songbirds are regularly taken in spring and summer. Holt, D. W., Berkley, R., Deppe, C., Enríquez Rocha, P. L., Olsen, P. D., Petersen, J. L., & Wood, K. L. (1999). The Californian population of a great horned owl is found at an elevation of 6,900 feet but those that live in Rockies make habitat at a height of 10,800 feet. These errant owls mainly hunt chickens, though will also take domestic guineafowl, turkeys and anything else available.  Most mortality in modern times is human-related, caused by owls flying into man-made objects, including buildings, cars, power lines, or barbed wire. In Brazil, it was found in a small study that birds overall outnumbered mammals in pellets, although most were not determined to species and the ones that were shown a tremendously diverse assemblage of birds with no obvious dietary preference. Eats some birds (especially in north), up to size of geese, ducks, hawks, and smaller owls. The skin of the feet and legs, though almost entirely obscured by feathers, is black. Two hare species, the black-tailed jackrabbit and snowshoe hare, are so important to the owls as a food source that the local owl populations sharply rise and fall in sync with the hares' cyclical population trends. A variable-sized white patch is seen on the throat. Diets of five species of desert owls. In courtship, male performs display flight, also feeds female. All subspecies are darkly barred to some extent along the sides, as well. Knopf, Fritz L. and Roger M. Evans.  The same species constituted 75% by number of a small sampling in Oklahoma. B., T. H. Craig, and O. D. Markham. Great horned owls do not really like to live in suburban areas although they do feel home at public parks.  The great horned owl has cylindrical eyes which creates more distance from the lens of the eye to the retina, which allows it to act more like a telephoto lens for farther distance sight compared to that possible from round eyes.  Species as large as adult Canada geese, snow goose and great blue herons have been successfully killed.  Mean body weight is 1,608 g (3.545 lb) for females and 1,224 g (2.698 lb) for males. At Kluane Lake in Yukon, incursions into neighboring territories were observed only twice—by females when neighboring female had died or emigrated, suggesting that territorial defense may be sex specific. Tribes in New Mexico were known to use owl wing feathers to produce arrows which could strike their enemies with a minimum of sound.  Young owls move onto nearby branches at 6 weeks and start to fly about a week later. If the intruder continues to press the confrontation, the defending owl will "hop" forward and strike it with feet, attempting to grasp and rake with claws. They likely fancy living in habitats which are dominated by old-growth trees. Aggressive and powerful in its hunting (sometimes known by nicknames such as "tiger owl"), it takes prey as varied as rabbits, hawks, snakes, and even skunks, and will even attack porcupines, often with fatal results for both prey and predator. , Great horned owls are frequently mobbed by other birds. Territories are established and maintained through hooting, with highest activity before egg-laying and second peak in autumn when juveniles disperse, and can range from an average of 16 km2 (6.2 sq mi) in Yukon to an average of 2.1 km2 (0.81 sq mi) in Wyoming.  Moles, of at least four or five species, are also widely but lightly reported as prey.  The capture of the hatchlings of very large reptiles such as loggerhead turtles (Caretta caretta) and American alligators (Alligator mississippiensis) by great horned owls has been reported, in both cases likely when the baby reptiles are attempting to make their way to the security of water.  Nesting owls at sites in Winnipeg, Manitoba began nesting five to six weeks earlier than those in rural parts of Manitoba, presumably due to experiencing an extremely warm winter by Winnipeg’s standards, as well as benefitting from the local urban heat island.