ORDER STRIGIFORMES (Owls)
Posted: Tue Mar 11, 2014 4:28 pm
A diverse order, owls range in size from sparrow- to eagle-sized. Over 200 species are distributed among approximately 27 genera. Owls are found world-wide, covering nearly all types of terrestrial habitats.
They are known for many characteristics, including their well-developed talons, soft plumage, and notoriously silent flight. Their legs are strong, and feathered in many species; they have zygodactyl raptorial feet. All species have a characteristic facial disk, which is circular among strigid owls and heart-shaped in the tytonid owls. Their holorhinal nostrils are found at the base of their short, downward-pointing bills, and their palates are desmognathous or schizognathous. They have unusually fleshy tongues, and lack crops, but have large caeca with club-shaped ends. Their large wings allow them to fly slowly, and their plumage is often cryptic, and many species have different color phases. Their feathers have either absent or rudimentary aftershafts. Most species are active hunters at night, and as such they have several important adaptations for this lifestyle. Their forward-facing eyes are large, elongated, and have slightly thickened corneas. The number of light-sensitive elements (rods) in their retinas is high, especially compared to other birds. This allows them a heightened sense of vision in dim light, but contrary to popular belief, they cannot see in total darkness. At least some species have been shown to have color vision. Their eyes are more or less fixed in their orbits, supported by a bony sclerotic ring. Therefore they have well-developed binocular vision, but they need to turn their heads to see on either side of them. Their hunting ability is also greatly augmented by their excellent sense of hearing, and some species use their auditory capabilities to hunt prey that they cannot see (such as rodents running under the snow in winter). The facial disk and facial ruff are both important in their sense of hearing. The facial ruff is composed of paired layers of densely packed feathers that have large rachides and reduced vanes; these are inserted behind the ear openings in a special flap of skin. The facial disk, which lies over the ruff, is composed of feathers with open vanes. Together these form parabolic troughs leading to the ears that can increase sound pressure tenfold. The facial ruff and disk are larger in highly nocturnal species, as well as those that hunt prey travelling under the snow. Their hearing is more sensitive to low-frequency sounds than most birds, and is sensitive across a wide range of frequencies. They have a wide outer ear tube and a large inner ear, and the auditory region of the brain has more nerve cells than that of other species of comparable size, which allows them to detect sounds more effectively.
Owls hunt a wide variety of prey, ranging from small mammals to birds, lizards, and insects; there are even fish-eating owls in Africa and Asia. Prey is often swallowed whole, and the fur, feathers, and bones are later regurgitated in pellets. Many owl species, especially those that hunt during night hours, are able to fly nearly silently. Several special feather adaptations make this possible. The leading edges of their outer primaries have stiff, comb-like fringes that reduce noise, the trailing edge of their primaries and secondaries have soft fringes that reduced turbulence behind the wings, and their primaries, secondaries, and wing coverts are covered in downy feathers that also reduce noise. Silent flight may be less important in those species that hunt over water or during the day, and many of these species do not have these adaptations.
Owls do not build nests, instead they use nests of other species or utilize tree cavities. Some nest on the ground and one species nests in underground burrows dug by mammals. In all species the female does the majority, if not all, of the incubation; the male hunts prey and feeds both the female and the young. Females are generally larger than males.
Links:
Africa Wild: Owls of the Kgalagadi
Africa Wild: Owls - Bird of the month December 2013
Two owl families are commonly recognized, the barn-owls (Tytonidae) and the typical-owls (Strigidae).
ORDER STRIGIFORMES
Family Tytonidae (Barn Owls)
Family Strigidae (Owls)
They are known for many characteristics, including their well-developed talons, soft plumage, and notoriously silent flight. Their legs are strong, and feathered in many species; they have zygodactyl raptorial feet. All species have a characteristic facial disk, which is circular among strigid owls and heart-shaped in the tytonid owls. Their holorhinal nostrils are found at the base of their short, downward-pointing bills, and their palates are desmognathous or schizognathous. They have unusually fleshy tongues, and lack crops, but have large caeca with club-shaped ends. Their large wings allow them to fly slowly, and their plumage is often cryptic, and many species have different color phases. Their feathers have either absent or rudimentary aftershafts. Most species are active hunters at night, and as such they have several important adaptations for this lifestyle. Their forward-facing eyes are large, elongated, and have slightly thickened corneas. The number of light-sensitive elements (rods) in their retinas is high, especially compared to other birds. This allows them a heightened sense of vision in dim light, but contrary to popular belief, they cannot see in total darkness. At least some species have been shown to have color vision. Their eyes are more or less fixed in their orbits, supported by a bony sclerotic ring. Therefore they have well-developed binocular vision, but they need to turn their heads to see on either side of them. Their hunting ability is also greatly augmented by their excellent sense of hearing, and some species use their auditory capabilities to hunt prey that they cannot see (such as rodents running under the snow in winter). The facial disk and facial ruff are both important in their sense of hearing. The facial ruff is composed of paired layers of densely packed feathers that have large rachides and reduced vanes; these are inserted behind the ear openings in a special flap of skin. The facial disk, which lies over the ruff, is composed of feathers with open vanes. Together these form parabolic troughs leading to the ears that can increase sound pressure tenfold. The facial ruff and disk are larger in highly nocturnal species, as well as those that hunt prey travelling under the snow. Their hearing is more sensitive to low-frequency sounds than most birds, and is sensitive across a wide range of frequencies. They have a wide outer ear tube and a large inner ear, and the auditory region of the brain has more nerve cells than that of other species of comparable size, which allows them to detect sounds more effectively.
Owls hunt a wide variety of prey, ranging from small mammals to birds, lizards, and insects; there are even fish-eating owls in Africa and Asia. Prey is often swallowed whole, and the fur, feathers, and bones are later regurgitated in pellets. Many owl species, especially those that hunt during night hours, are able to fly nearly silently. Several special feather adaptations make this possible. The leading edges of their outer primaries have stiff, comb-like fringes that reduce noise, the trailing edge of their primaries and secondaries have soft fringes that reduced turbulence behind the wings, and their primaries, secondaries, and wing coverts are covered in downy feathers that also reduce noise. Silent flight may be less important in those species that hunt over water or during the day, and many of these species do not have these adaptations.
Owls do not build nests, instead they use nests of other species or utilize tree cavities. Some nest on the ground and one species nests in underground burrows dug by mammals. In all species the female does the majority, if not all, of the incubation; the male hunts prey and feeds both the female and the young. Females are generally larger than males.
Links:
Africa Wild: Owls of the Kgalagadi
Africa Wild: Owls - Bird of the month December 2013
Two owl families are commonly recognized, the barn-owls (Tytonidae) and the typical-owls (Strigidae).
ORDER STRIGIFORMES
Family Tytonidae (Barn Owls)
Family Strigidae (Owls)