This family of owls includes two extant genera and approximately 16 species, though the taxonomy is under frequent revision. They are found mainly in tropical regions, with several species, including the common barn-owl, ranging to higher latitudes. Most species are forest-dwelling, though several species are found in open woodland areas, and the grass-owls live in open grasslands.
Morphologically, the tytonid owls vary from their strigid relatives in several characteristics. These owls have a heart-shaped facial disk, an elongated, compressed bill, and proportionately smaller eyes than Strigidae owls. They have long legs, and their inner toe, which is as long as the middle one, has a pectinate claw. Their sternum has two notches and is fused with the furcula. Like the other owls, however, their talons are well developed, and their fourth toe is reversible. Females are generally larger than males, and may have darker spots. Their plumage is soft and dense, generally darker with markings on the upperparts, while the underparts are pale and often without any markings. As in all owls, they have an unusually fleshy tongue and well-developed intestinal caeca, and they lack a crop as found in most birds.
The tytonid owls are perhaps best known for the well-studied common barn-owl, Tyto alba. Many other species are known little, if at all, and we can only assume that their behavior patterns are similar. Tytonid owls tend to feed on small mammals when available, with rodents, shrews, and voles important in the diet. However, they are capable of adapting to locally available prey, and have been known to prey on many species of birds, especially shorebirds, as well as reptiles, frogs, and insects. They often carry their prey in their bill, unlike other birds of prey that carry their prey in their talons.
Most species can fly nearly silently; there are several feather adaptations that allow this to happen (see Strigiformes). They have large, broad wings that allow slow flight; many species will hunt while slowly soaring near the ground. Most species within this family are nocturnal, and their excellent vision and hearing allows them to hunt with high accuracy in very poor light (see Strigiformes for details). They tend to remain solitary or in pairs throughout the year, and may occupy a territory year-round; most species are sedentary and after fledging do not travel far from their natal site. Again, much of what we know about reproductive behavior comes from the common barn-owl, which may have low breeding rates, especially in unfavorable conditions. Egg-laying varies with weather and prey cycles, so that females will lay eggs when their prey species are also reproducing. Clutch sizes are variable within the family, ranging from small (1-2 eggs) to larger clutches (4-7 eggs). Most species within this family nest in tree cavities, barn-owls may take advantage of man-made structures such as barns and church steeples. The grass-owls nest on the ground, burrowing a system of tunnels through long grasses to a nesting site. Females are usually the sole incubators, while the males provide food, though both will care for the young once hatched. Sensitive to disturbance, the tytonid owls are known for their threat displays. When confronted with danger, the owl will bow towards the intruder, spreading its wings and tail, hissing and snapping its bill; if the intruder is not frightened off, the owl will proceed to move its head up and down while shaking it, still hissing. The bowing and head shaking aspects of the threat display seem to be unique to this family.
There is some debate regarding the taxonomy within Tytonidae. The number of species recognized within the subfamily Tytoninae (genus Tyto) varies, and the position of the subfamily Phodilinae, currently included within this family, has been argued as well.
In the past few hundred years, as people started to recognize the value of owls for rodent control, their presence has become welcome on farms. They have also been used for biological control, introduced into various islands with the idea that they would control outbreaks of rodent pests. However, these experiments have had disastrous results. When they were introduced into the Seychelle Islands in the 1950s, for example, they began to prey on local seabird populations, with devastating effects. By 1960, people recognized their error and had to begin hunting them. Unfortunately, this mistake has happened more than once, as the owls' ability to prey on small birds is often overlooked. Currently, the greatest diversity of tytonid species lives in the tropics. Five species in this family may be considered threatened, one of which is endangered. They can be extremely sensitive to habitat destruction.
At present, the oldest reliable fossil from this family is a tarsometatarsus that was found in Colorado, dating back to the Paleocene epoch (58 MYA). The only other Paleocene fossils found to date include two owls from France. There seemed to be a major radiation during the Eocene, with at least four families in existence, though three of those are now extinct. By the end of the Paleogene, Tytonidae was a highly diverse family, and the genus Tyto dates at least to the mid Miocene.
Owls have been part of human folklore since ancient times, common across many cultures. The common barn-owl, especially, has been part of many myths, even dating back to ancient Egypt. Wall paintings and mummified remains of these owls have been discovered, and it appears that some of the ancient Egyptians believed that the 3rd human soul was reincarnated as a human-headed bird that remains near the burial site of the dead. The owl motif was used in Egyptian as well as Mayan hieroglyphics. The Zapotecs of Mexico believed that the owl was associated with death, in that it gives notice when a man dies before flying off to retrieve his soul. Owls have been used in various medicinal potions and remedies, and represented a myriad of ideals and superstitions to many different people, from courage, strength, wisdom, to trickery and evil.
Campbell, B. & E. Lack, eds. 1985. A dictionary of birds. Buteo Books, Vermillion, South Dakota.
del Hoyo, J., Elliott, A., & J. Sargatal. 1992. Handbook of the birds of the world, volume 5. Lynx Edicions, Barcelona.
Feduccia, A. 1999. The origin and evolution of birds. Yale University Press, New Haven.
Johnsgard, P.A. 1998. North American owls: biology and natural history. Smithsonian Inst. Press, Washington.
Sibley & Ahlquist. 1990. Phylogeny & classification of birds: a study in molecular evolution. Yale Univ. Press, New Haven.
Thomson, A. 1964. A new dictionary of birds. British Ornithologists' Union. McGraw-Hill Book Co., NY.
Danielle Cholewiak (author).
uses sound to communicate
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
having the capacity to move from one place to another.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
uses sight to communicate