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Strigiformes - Nocturnal Birds of Prey (Owls)
 
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Strigiformes
Families: Tytonidae - Barn Owls, Strigidae - Typical Owls
 
Images:   
Eastern Screech Owl
 
  Order Strigiformes - Nocturnal Birds of Prey (Owls)
Wiki     ToL     EoL
EXAMPLE
  178 species, 25 genera (Sibley & Monroe, 1990). Clements (2007) lists 215 species. Dickinson (2003) and Harris (2009) list 195 species, 29 genera. Widely distributed in all regions of the world including sub-polar areas (Barn Owls are absent in polar areas and in Asia north of the Himalayas).
   There are two families in this order:
      Family Tytonidae - Barn Owls
      Family Strigidae - Typical Owls

   Owls are a relatively homogeneous group. They are solitary nocturnal or crepuscular predators. Raptorial adaptations of feet and bill, soft plumage, and mainly nocturnal habits set them apart from other birds. Goatsuckers may be their closest ancient relatives but this is not supported by current evidence. It is probably best to consider owls, nightjars (caprimulgids), falcons, and accipitrids as distinct orders.
   Owls have a fleshy tongue and no crop. Their bills are curved with a sharp tip for tearing prey. They have a disc of stiff feathers surrounding the face. The outer toe (4th) is reversible (zygodactyl) and the feet are raptorial (they have long, curved, sharp "raptorial" claws). Their eyes are large and directed forward to provide binocular vision and depth perception. (Their eyes are fixed in the sockets so they must turn their head to change views.) The face is surrounded by a facial disc of specialized feathers. (The facial disc is located behind the ear openings.) Their nostrils are hidden by stiff bristles and are holorhinal and impervious. Their palate is approximately schizognathous. Their pelvic muscles are AD. They have two carotids. Flexor tendons are Type 1. The hypotarsus is simple. The syrinx is bronchial with one pair of muscles. They have a soft plumage and fly very quietly to remain hidden to their potential prey. They have 11 primaries, 12-18 secondaries and 12 (10-13) tail feathers. They have 14 cervical vertebrae. The caeca are large and long with expanded ends. The oil gland is naked or minutely tufted. The smallest owl (Elf Owl, Micrathene whitneyi) weighs about 31 g. The largest are the eagle owls (Bubo) which weigh ~4.5 kg (10 lb) and have a wing span of 2 meters.
   Owls do not build a true nest - most deposit their eggs in a hole, on the ground, or in the nest of another bird. Great Horned Owls, Bubo virginianus, may use the nest of a Bald Eagle, Haliaeetus leucocephalus. The Burrowing Owl, Athene cunicularia, uses the hole of a prairie dogs or a ground squirrel. Owls often begin reproduction in the winter when nights are the longest. Eggs are white and almost round. Clutches vary from 1-14 eggs, often depending on food supply. Incubation begins with the first egg so hatching is asynchronous. Young vary in size and the largest (oldest) gets the surest food supply - thus the number fledged depends on the food available. The female incubates and the male brings food to her. Both parents may feed the young, Incubation is relatively long (32-34 days in the Barn Owl, 26-28 in the Short-eared Owl, Asio flammeus, etc. Young are nidicolous, blind, and covered with whitish down which is replaced by a second downy plumage, followed by true feathers. Owls reach maturity at one year. Smaller owls may live more than 10 years, larger owls more than 20.
   Owls are carnivorous - most feed on rodents and shrews. Some take birds, reptiles, amphibians, fish, crabs, crayfish, earthworms, or insects. Fish-eating owls (not found in North America) have bare legs and spiny soles and catch fish in their talons from the surface. Some smaller owls may take moths and other insects in flight. Owls hunt by stealth and surprise. Their dull colors make them difficult to see under low lilght conditions and the leading edges of their wing feathers are serrated and muffle sound as they fly - they are nearly silent (some of the fish-eating owls lack this adaptation). Once captured, prey items are killed, usually with a bite, and they are swallowed whole. With larger animals, the owl may use the bill to chew the body from head to toe crushing ribs and softening other obstructions that might make swallowing more difficult. Still larger prey is dismantled using the bill while it is held or anchored by a foot.
   Less digestible remains (bones, teeth, hair, feathers, chitin) are regurgitated as pellets. They can give some idea of the bird's diet.
   The eggs of most owls are white and spherical - ranging from 2 or so to a dozen. They are laid at 2-3 day intervals and incubation begins with the first or second egg so hatching is asynchronous. The oldest chicks (usually 1) survives unless food is superabundant. Owls don't really build nests - they find shelter in an abandoned nest of another species, in tree cavities, underground burrows, or barns and buildings.
   Owls have excellent vision but are specialized to see in low-light conditions and probably give up color-vision for this ability. While a few hunt in the day (Burrowing Owls and species of the far north in summer), many are crepuscular or concentrate their feeding in the early night hours when some shred of twilight remains. Owls do not like to fly when it is totally dark - possibly because they can't see branches and obstructions - but many do not need vision to hunt successfully. Most owls are able to locate their prey by sound. The symmetrical ears of other birds are able to locate a sound source in two dimensions. Owls have two solutions for locating sounds in three dimensions:
   (1) In barn owls, there is a fleshy flap in front of each ear opening. They are, however slanted in different orientations relative to vertical on opposite sides. Sounds are reflected by the hard feathers of the facial disc and different portions of the disc are sampled by reflection from the asymmetrical flaps to the ear openings. (These flaps can be moved to track sounds.) This enables the bird  to locate prey in 3 dimensions. Under experimental conditions, I've "seen" them make perfect strikes on moving prey in total darkness!                                                                Wiki
   (2) In strigid owls, the ear canals themselves open asymmetrically on the two sides of the head (the opening is lower on one side, higher on the other - ears begin as symmetrical structures but various mechanisms lead to a differentiation of the two external openings). This enables them to locate prey three dimensionally based on differences in the sounds sampled from each side of the facial disc.                                    Wiki
   With excellent hearing, owls do much of their communicating by voice. Their calls are often loud and tend to travel much farther at night. We often locate them by listening for their calls in winter and early spring. It is possible to imitate the call of the Eastern Screech-Owl and "talk" back and forth with them. Take an "owling" drive around the island in the winter. You should hear our common owls (Eastern Screech-Owl, Barred Owl, and Great Horned Owl) although our Barred Owls may be rarer than they should be.
 
  Family Tytonidae - Barn Owls, Grass Owls, Bay Owls
Wiki     ToL     EoL
EXAMPLE
  15 (16) species, 1 (2) genera (Tyto, Phodilus). Worldwide in tropical and temperate regions (except Hawaii and New Zealand). Missing in Asia north of the Himalayas. Bay Owls (Phodilus, 2 spp) are nocturnal and similar to other barn owls. They have ear tufts and a U-shaped facial disk. They are found in southeast Asia.
   Medium-sized owls. They are characterized by a large facial disc, soft plumage, and screeching calls. Their propensity for nesting in buildings and their eerie calls (screeches, screams, metallic whistles, etc.) have given rise to the belief that the structures are haunted.
   Most species have an oval, rounded, squares, or heart-shaped facial disc of hard feathers. They pick up sound and reflect it to asymmetric flaps that reflect it to symmetrical ears. This differential sound enables owls to locate prey in 3 dimensions using sound. The skull is long and narrow. Their wings are broad and give them a buoyant, silent flight. Their legs are long and feathers on the posterior side of the tarsus point upward. The inner toe is as long as the middle toe and the claw of the middle toe is "comb-like" (pectinate). The sternum is without a manubrium. Furcula are fused to the keel. Contour feathers have a small aftershaft.
   Barn owls have soft plumage, often cryptically colored. The face (inside the disk) may be white, cream, or gray and is delimited by a narrow darker border. The head and upperparts vary from brown to gray or blackish. All are spotted with white beneath and black above.
   Most are crepusular - you would be most likely to see a Barn Owl flying hunting over our salt marsh at dusk. They can hunt in total darkness. They are usually solitary or pairs that hold a territory throughout the year. They are found in forests, swamps and the open edges of farmland. In the southeast they are most likely in farmland or marsh with abandoned buildings and scattered trees. They are relatively sedentary.
   Barn owls feed on small mammals, small birds, frogs, reptiles, and large insects taken in flight. They will capture Tree Swallows in the spring and fall as they move through in large flocks. When they strike, all four toes are extended and contact the ground about equidistant from each other. This gives the owl the best chance that one of the nails will encounter the prey.
   They nest in tree cavities, nest boxes, or even on the ground. On Sapelo Island in Georgia, Barn Owls prefer abandoned structures - the barn at Chocolate (second floor), the bell tower of the church at Racoon Bluffs (before it collapsed), steps in the old lighthouse (before it was rebuilt), or the old fog horn tower., etc. They lay 4-7 eggs. The female incubates for 27-34 days and young fledge when 6-7 weeks of age. If food is scarce, the younger  chicks are usually eaten by the older sibs. 
  Chocolate






  Barn at
  Chocolate,
  Sapelo Island,
  GA
Racoon Bluffs





 
  Old Church,
  Racoon Bluffs,
  Sapelo Island,
  GA
Lighthouse




 
  Lighthouse,
  before
  restoration -
  Sapelo Island,
  GA
   
Barn Owl nest sites in Georgia
 
 
  Family Strigidae - Typical Owls
Wiki     ToL     EoL
EXAMPLE
  161 (199) species, 23 genera. Dickinson (2003) and Harris (2009) include 180 species, 27 genera. Worldwide, including subpolar latitudes. Some of the genera of interest to us in North America include: Megascops - screech owls (~20 species, including the Eastern Screech Owl); Bubo - horned owls, eagle-owls, fish-owls (~25 species, including Great-horned Owl, Snowy Owl ); Strix - earless owls (~15 species, including Northern Spotted Owl); Micrathene - Elf Owl; Aegolius - saw-whet owls (4 species, Saw-whet Owl); Asio - eared owls (6-7 species, including Long-eared Owl, Short-eared Owl).
   Owls have a rounded facial disc - a circle of feathers around each eye - framed by a narrow ruff of feathers. They have a large head with large, forward-directed eyes giving acute binocular vision in dim light. Their skull is relatively broad. The facial disk is more or less circular. This disk focuses sound reflection toward the asymmetric ear openings, permitting them to locate prey by sound in three dimensions. Their beak is hooked and raptor like. Most owls are brown, red-brown, or buff - heavily streaked or barred with spots or streaks aiding in their camouflage (the Snowy Owl, Bubo scandiacus, is largely white or white with black bars). Several species have ear tufts. One to six of the primaries have their inner web emarginate. Their leading edge is serrated giving the birds almost silent flight. Their legs and feet are powerful. The inner toe is shorter than the middle toe (and the middle claw is not pectinate). The tail is rounded and relatively short. The sternum has a manubrium (presternum). The furcula are free from the keel. Feathers on the tarsus point downward. There is no aftershaft with contour feathers.
   Owls are generally crepuscular (perching in cover during the day). If discovered by jays, crows, or other species, the may be "mobbed" - harassed. (Check out loud gatherings around trees - there may be an owl or hawk at the center of the group.) They are carnivorous (above). Owls are generally vocal using calls to defend territory and attract mates. Paired birds may duet.
   Owls range from Arctic tundra to equatorial forests. Most species are sedentary but more northern populations are nomadic (irruptive) or migratory. Their diets are discussed above.
   Typical owls are usually monogamous with long-lasting pair bonds. They nest in other birds' nests, cavities, caves, nest boxes, or even buildings. A few are ground-nesters. The Burrowing Owl, Athene cunicularia, uses underground burrows made by mammals (prairie dogs, etc.). Clutches are between 2-23 eggs. They are laid at intervals of 1-3 days and incubation begins with the first so hatching is asynchronous. Thus the older chick is stronger and can compete for food. When more food is available, the two older chicks may survive. Etc. Cannibalism of younger chicks by the older is not uncommon. Incubation takes 22-35 days. The female incubates and broods - she is fed by the male until the chicks can be left alone on the nest. Offspring of larger owls may remain dependent on their parents for 5 months or more.
 
Eastern Screech Owl
Young Eastern Screech Owl, Otus asio.
Ohio
                                                     SI Web
 
       
    Banner - Barred Owl. Francis Beidler Forest.