Strigidae Temporal range: Early Eocene to present | |
---|---|
Eastern screech owl | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Aves |
Order: | Strigiformes |
Family: | Strigidae Leach, 1819 |
Type genus | |
Strix Linnaeus, 1758 | |
Genera | |
some 25, see text | |
Synonyms | |
Striginae sensu Sibley & Ahlquist |
The true owls or typical owls (family Strigidae) are one of the two generally accepted families of owls, the other being the barn owls (Tytonidae). This large family comprises 230 living or recently extinct species in 24 genera. The Strigidae owls have a cosmopolitan distribution and are found on every continent except Antarctica.
While typical owls (hereafter referred to simply as owls) vary greatly in size, with the smallest species, the elf owl, being a hundredth the size of the largest, the Eurasian eagle-owl and Blakiston's fish owl, owls generally share an extremely similar body plan. [1] They tend to have large heads, short tails, cryptic plumage, and round facial discs around the eyes. The family is generally arboreal (with a few exceptions like the burrowing owl) and obtain their food on the wing. The wings are large, broad, rounded, and long. As is the case with most birds of prey, in many owl species females are larger than males. [2]
Because of their nocturnal habits, they tend not to exhibit sexual dimorphism in their plumage. Specialized feathers and wing shape suppress the noise produced by flying, both taking off, flapping and gliding. [3] This silent flight allows owls to hunt without being heard by their prey. Owls possess three physical attributes that are thought to contribute to their silent flight capability. First, on the leading edge of the wing, there is a comb of stiff feathers. Second, the trailing edge of the wing contains a flexible fringe. [4] Finally, owls have downy material distributed on the tops of their wings that creates a compliant but rough surface (similar to that of a soft carpet). All these factors result in significant aerodynamic noise reductions. [5] The toes and tarsi are feathered in some species, and more so in species at higher latitudes. [6] Numerous species of owls in the genus Glaucidium and the northern hawk-owl have eye patches on the backs of their heads, apparently to convince other birds they are being watched at all times.[ citation needed ] Numerous nocturnal species have ear-tufts, feathers on the sides of the head that are thought to have a camouflage function, breaking up the outline of a roosting bird. The feathers of the facial disc are arranged in order to increase sound delivered to the ears.[ citation needed ] Hearing in owls is highly sensitive and the ears are asymmetrical allowing the owl to localise a sound in multiple directions. Owls can pinpoint the position of prey, such as a squeaking mouse, by computing when the sound from the object reaches the owl's ears. If the sound reaches the left ear first, the mouse must be to the left of the owl. The owl's brain will then direct the head to directly face the mouse. [7] In addition to hearing, owls have massive eyes relative to their body size. Contrary to popular belief, however, owls cannot see well in extreme dark and are able to see well in the day. [1]
Owls are also able to rotate their heads by as much as 270 degrees in either direction without damaging the blood vessels in their necks and heads, and without disrupting blood flow to their brains. Researchers have found four major biological adaptations that allow for this unique capability. First, in the neck there is a major artery, called the vertebral artery, that feeds the brain. This artery passes through bony holes in the vertebra. These bony holes are ten times larger in diameter than the artery that passes through them (extra space in the transverse foramina) which creates air pockets that allow for more movement of the artery when twisted. 12 of the 14 cervical vertebrae in the owl's neck have this adaptation. This vertebral artery also enters the neck higher up than it does in other birds. Instead of going in at the 14th cervical vertebrae, it enters in at the 12th cervical vertebrae. Finally, the small vessel connection between the carotid and the vertebral arteries allow the exchanging of blood between two blood vessels. These cross connections allow for uninterrupted blood flow to the brain. This means that even if one route is blocked during extreme head rotations, another route can continue blood circulation to the brain. [8]
Several owl species also have fluorescent pigments called porphyrins under their wings. A large group of pigments defined by nitrogen-containing pyrole rings, including chlorophyll and heme (in animal blood), make up the porphyrins. Other bird species will use porphyrins to pigment eggshells in the oviduct. Owl species, however, use porphyrins as a pigment in their plumage. Porphyrins are most prevalent in new feathers and are easily destroyed by sunlight. Porphyrin pigments in feathers fluoresce under UV light, allowing biologists to more accurately classify the age of owls. The relative ages of the feathers are differentiated by the intensity of fluorescence that they emit when the primaries and secondaries are exposed to black light. This method helps to detect the subtle differences between third and fourth generation feathers, whereas looking at wear and color makes age determination difficult. [9]
It has been noted that there is some competition for niche space between the spotted owl and the barred owl (both of which are true owls) . This competition is related to deforestation, and therefore a reduction in niche quantity and quality. This deforestation is more specifically the result of overlogging and forest fires. These two species of owl are known to traditionally live in mature forests of old and tall trees, which at this point in time are mostly limited to public lands. As niche overlap is occurring in these two families, there is a concern with the barred owls encroaching on the spotted owl's North American habitats, causing a decline of the spotted owl. [10] As noted above, these species prefer mature forests which, due to deforestation, are at limited supply and take a long time to reestablish after deforestation has occurred. Because the northern spotted owl shares its territories and competes with other species, it is declining at a more rapid pace. This invasion by barred owls occurred about 50 years ago in the Pacific Northwest, and despite their low numbers, they are considered an invasive species because of the harm done to native spotted owls. In this competition for resources, hunting locations and general niches, the barred owl is pushing the spotted owl to local extinction. It is thought that the rapid decrease in population size of spotted owls will cause a trophic cascade, since the spotted owls help provide a healthy ecosystem. [11]
Owls are generally nocturnal and/or crepuscular and spend much of the day roosting. They are often misperceived as ‘tame’ since they allow humans to approach quite closely before taking flight, but in reality they are attempting to avoid detection through stillness. Their cryptic plumage and the inconspicuous locations they adopt are an effort to avoid predators and mobbing by small birds. [12]
Owls, such as the eagle-owl, will use visual signaling in intraspecific communication (communication within the species), both in territorial habits and parent-offspring interactions. Some researchers believe owls can employ various visual signals in other situations involving intraspecific interaction. Experimental evidence suggests that owl feces and the remains of prey can act as visual signals. This new type of signaling behavior could potentially indicate the owls' current reproductive state to intruders, including other territorial owls or non-breeding floaters. Feces are an ideal material for marking due to its minimal energetic costs, and can also continue to indicate territorial boundaries even when occupied in activities other than territorial defense. Preliminary evidence also suggests that owls will use feces and the feathers of their prey to signal their breeding status to members within the same species. [13]
Some species of owl are migratory. One such species, the northern saw-whet owl, migrates south even when food and resources are ample in the north. [14]
Some owls have a higher survival rate and are more likely to reproduce in a habitat that contains a mixture of old growth forests and other vegetation types. Old growth forests provide ample dark areas for owls to hide from predators [15] Like many organisms, spotted owls rely on forest fires to create their habitat and provide areas for foraging. Unfortunately, climate change and intentional fire suppression have altered natural fire habits. Owls avoid badly burned areas but they benefit from the mosaics of heterogeneous habitats created by fires. This is not to say that all fires are good for owls. Owls only thrive when fires are not of high severity and not large stand-replacing (high-severity fires that burn most of the vegetation) which create large canopy gaps that are not adequate for owls. [16]
Avian malaria or Plasmodium relictum affects owls and specifically, 44% of northern and Californian spotted owls harbor 17 strains of the parasite. As mentioned in the niche competition section above, spotted owls and barred owls are in competition so their niche overlap may be resulting in the plasmodium parasite having more hosts in a concentrated area but this is not certain. [17]
The main predators of owls are other species of owls. An example of this occurs with the northern saw-whet owl that lives in the northern U.S. and lives low to the ground in brushy areas typically of cedar forests. These owls eat mice, and perch in trees at eye level. Their main predators are barred owls and great horned owls. [18]
The family Strigidae was introduced by the English zoologist William Elford Leach in a guide to the contents of the British Museum published in 1819. [19] [20]
A molecular phylogenetic study of the owls by Jessie Salter and collaborators published in 2020 found that the family Strigidae was divided into two sister clades and some of the traditional genera were paraphyletic. The placement of three monotypic genera remained uncertain due to the degraded nature of the available DNA. [21] Based on these results Frank Gill, Pamela Rasmussen and David Donsker updated the online list of world birds that they maintain on behalf of the International Ornithological Committee (IOC). [22]
The cladogram below is based on the results of the study by Salter and collaborators published in 2020. [21] The subfamilies are those defined by Edward Dickinson and James Van Remsen Jr. in 2013. [23] A genetic study published in 2021 suggested that the genus Scotopelia may be embedded within Ketupa. [24]
Strigidae |
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
The 235 extant or recently extinct species are assigned to 23 genera: [22]
The fossil database for Strigiformes is highly diverse and shows an origin from ~60MYA into the Pleistocene. The maximum age range for the Strigiformes clade extends to 68.6MYA. [26]
Placement unresolved:
The supposed fossil heron "Ardea" lignitum (Late Pliocene of Germany) was apparently a strigid owl, possibly close to Bubo. [30] The Early–Middle Eocene genus Palaeoglaux from west-central Europe is sometimes placed here, but given its age, it is probably better considered its own family for the time being.
Owls are birds from the order Strigiformes, which includes over 200 species of mostly solitary and nocturnal birds of prey typified by an upright stance, a large, broad head, binocular vision, binaural hearing, sharp talons, and feathers adapted for silent flight. Exceptions include the diurnal northern hawk-owl and the gregarious burrowing owl.
The bird family Tytonidae, which includes the barn owlsTyto and the bay owlsPhodilus, is one of the two families of owls, the other being the true owls or typical owls, Strigidae. They are medium to large owls with large heads and characteristic heart-shaped faces. They have long, strong legs with powerful talons. They also differ from the Strigidae in structural details relating in particular to the sternum and feet.
The American horned owls and the Old World eagle-owls make up the genus Bubo, at least as traditionally described. The genus name Bubo is Latin for owl.
The snowy owl, also known as the polar owl, the white owl and the Arctic owl, is a large, white owl of the true owl family. Snowy owls are native to the Arctic regions of both North America and the Palearctic, breeding mostly on the tundra. It has a number of unique adaptations to its habitat and lifestyle, which are quite distinct from other extant owls. One of the largest species of owl, it is the only owl with mainly white plumage. Males tend to be a purer white overall while females tend to have more extensive flecks of dark brown. Juvenile male snowy owls have dark markings that may appear similar to females until maturity, at which point they typically turn whiter. The composition of brown markings about the wing, although not foolproof, is the most reliable technique to age and sex individual snowy owls.
The barred owl, also known as the northern barred owl, striped owl or, more informally, hoot owl or eight-hooter owl, is a North American large species of owl. A member of the true owl family, Strigidae, they belong to the genus Strix, which is also the origin of the family's name under Linnaean taxonomy. Barred owls are largely native to eastern North America, but have expanded their range to the west coast of North America where they are considered invasive. Mature forests are their preferred habitat, but they can also acclimatise to various gradients of open woodlands. Their diet consists mainly of small mammals, but this species is an opportunistic predator and is known to prey upon other small vertebrates such as birds, reptiles, and amphibians, as well as a variety of invertebrates.
The eastern screech owl or eastern screech-owl, is a small owl that is relatively common in Eastern North America, from Mexico to Canada. This species resides in most types of woodland habitats across its range, and is relatively adaptable to urban and developed areas compared to other owls. Although it often lives in close proximity to humans, the eastern screech owl frequently avoids detection due to its strictly nocturnal habits.
The brown fish owl is a fish owl species in the family known as typical owls, Strigidae. It is native from Turkey to South and Southeast Asia. Due its wide distribution it is listed as Least Concern on the IUCN Red List. It inhabits forests and wooded wetlands. Of the four living species of fish owl, it is the most widely distributed, most common and best-studied. It occupies a range of over 7,000 km (4,300 mi).
The spot-bellied eagle-owl, also known as the forest eagle-owl is a large bird of prey with a formidable appearance. It is a forest-inhabiting species found in the Indian Subcontinent and Southeast Asia. This species is considered part of a superspecies with the barred eagle-owl, which looks quite similar but is allopatric in distribution.
Tyto is a genus of birds consisting of true barn owls, grass owls and masked owls that collectively make up all the species within the subfamily Tytoninae of the barn owl family, Tytonidae.
Asio is a genus of typical owls, or true owls, in the family Strigidae. This group has representatives over most of the planet, and the short-eared owl is one of the most widespread of all bird species, breeding in Europe, Asia, North and South America, the Caribbean, Hawaii and the Galápagos Islands. Its geographic range extends to all continents except Antarctica and Australia.
Strix is a genus of owls in the typical owl family (Strigidae), one of the two generally accepted living families of owls, with the other being Tytonidae. Common names are earless owls or wood owls, though they are not the only owls without ear tufts, and "wood owl" is also used as a more generic name for forest-dwelling owls.
Ninox is a genus of true owls comprising 36 species found in Asia and Australasia. Many species are known as hawk-owls or boobooks, but the northern hawk-owl is not a member of this genus.
The giant Cuban owl or giant cursorial owl (Ornimegalonyx) is an extinct genus of giant owl that measured 1.1 metres in height. It is closely related to the many species of living owls of the genus Strix. It was a flightless or nearly flightless bird and it is believed to be the largest owl that ever existed. It lived on the island of Cuba.
The barred eagle-owl, also called the Malay eagle-owl, is a species of eagle owl in the family Strigidae. It is a member of the large genus Ketupa, which is found on most of the world's continents. This relatively little-known species is found from the southern Malay Peninsula down a string of several of the larger southeast Asian islands to as far as Borneo. It forms a superspecies with the physically similar but larger spot-bellied eagle-owl, although the two species appear to be allopatric in distribution.
Ketupa is a genus of owls in the family Strigidae. The genus formerly contained just three species, the fish owls but based on the results from a genetic study published in 2020, the generic boundaries were altered. The genus now contains twelve species, nine of which were formerly placed in the genus Bubo.
The buffy fish owl, also known as the Malay fish owl, is a fish owl in the family Strigidae. It is native to Southeast Asia and lives foremost in tropical forests and wetlands. Due to its wide distribution and assumed stable population, it is listed as Least Concern on the IUCN Red List since 2004.
The crested owl is a species of owl in the family Strigidae. It is the only species (monotypic) in the genus Lophostrix. It is a resident bird and occurs in Central America and northern South America. It is a medium-sized owl, easily recognizable with its very long whitish ear tufts and otherwise darker appearance. It inhabits lowland rainforests and prefers old growth in proximity with water. The crested owl is a strictly nocturnal species, but very little is known about its behaviour.
Screech owls are typical owls (Strigidae) belonging to the genus Megascops with 22 living species. For most of the 20th century, this genus was merged with the Old World scops owls in Otus, but nowadays it is again considered separately based on a range of behavioral, biogeographical, morphological, and DNA sequence data.
The tawny owl, also called the brown owl, is a stocky, medium-sized owl in the family Strigidae. It is commonly found in woodlands across Europe, as well as western Siberia, and has seven recognized subspecies. The tawny owl's underparts are pale with dark streaks, whilst its upper body may be either brown or grey. The tawny owl typically makes its nest in a tree hole where it can protect its eggs and young against potential predators. It is non-migratory and highly territorial: as a result, when young birds grow up and leave the parental nest, if they cannot find a vacant territory to claim as their own, they will often starve.
The tawny owl was first described by Swedish naturalist Carl Linnaeus in the tenth edition of his Systema Naturae in 1758, under its current scientific name Strix aluco. The binomial derives from the Greek strix "owl" and Italian allocco "tawny owl". Some early descriptions upon review were found to have somehow conflated the very different barn owl by describing it with the same scientific name Strix aluco, which in turn engendered some confusion.