True owl

True owl
Temporal range: Early Eocene to present
Eastern screech owl
Scientific classification
Kingdom:Animalia
Phylum:Chordata
Class:Aves
Order:Strigiformes
Family:Strigidae
Leach, 1820
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). The Sibley-Ahlquist taxonomy unites the Caprimulgiformes with the owl order; here, the typical owls are a subfamily Striginae. This is unsupported by more recent research (see Cypselomorphae for details), but the relationships of the owls in general are still unresolved. This large family comprises nearly 220 living species in 25 genera. The typical owls have a cosmopolitan distribution and are found on every continent except Antarctica.

Morphology

Cross sectioned great grey owl specimen showing the extent of the body plumage, Zoological Museum, Copenhagen

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. The feathers are soft and the base of each is downy, allowing for silent flight. The toes and tarsi are feathered in some species, and more so in species at higher latitudes.[3] 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. 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. Hearing in owls is highly sensitive and the ears are asymmetrical allowing the owl to localise a sound in multiple directions. 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]

Behavior

Owls are generally nocturnal and spend much of the day roosting. They are often perceived as tame since they allow people to approach quite closely before taking flight, but they are instead attempting to avoid detection. The cryptic plumage and inconspicuous locations adopted are an effort to avoid predators and mobbing by small birds.[4]

Systematic

Skeleton of Strigidae. Muséum de Toulouse

The family Strigidae was introduced by the English zoologist William Elford Leach in a guide to the contents of the British Museum published in 1820.[5][6]

The nearly 220 extant species are assigned to a number of genera, which are in taxonomic order:

  • Genus Megascops – screech-owls, some 20 species
  • Genus Otus – scops owls; probably paraphyletic, about 45 species
  • Genus Pyrroglaux – Palau owl
  • Genus Margarobyas – bare-legged owl or Cuban screech-owl
  • Genus Ptilopsis – white-faced owls, two species
  • Genus Bubo – horned owls, eagle-owls and fish-owls; paraphyletic with Nyctea, Ketupa and Scotopelia, some 25 species
  • Genus Strix – earless owls, some 19 species, including four that were previously classified as Ciccaba
  • Genus Ciccaba – the four species have been transferred to Strix
  • Genus Lophostrix – crested owl
  • Genus Jubula – maned owl
  • Genus Pulsatrix – spectacled owls, three species
  • Genus Surnia – northern hawk-owl
Tawny owl
  • Genus Glaucidium – pygmy owls, about 30–35 species
  • Genus Xenoglaux – long-whiskered owlet
  • Genus Micrathene – elf owl
  • Genus Athene – two to four species (depending on whether Speotyto and Heteroglaux are included or not)
The forest owlet, one of the critically endangered owls found in Central Indian Forest

Recently extinct

  • Genus Mascarenotus – Mascarene owls, three species (extinct c. 1850)
  • Genus Sceloglaux – laughing owl (extinct ~1914)

Late Quaternary prehistoric extinctions

  • Genus Grallistrix – stilt-owls, four species
    • Kaua‘i stilt-owl, Grallistrix auceps
    • Maui stilt-owl, Grallistrix erdmani
    • Moloka‘i stilt-owl, Grallistrix geleches
    • O‘ahu stilt-owl, Grallistrix orion
  • Genus Ornimegalonyx – Caribbean giant owls, one or two species
    • Cuban giant owl, Ornimegalonyx oteroi
    • Ornimegalonyx sp. – probably subspecies of O. oteroi
  • Genus Asphaltoglaux

Fossil record

  • Mioglaux (Late Oligocene? – Early Miocene of WC Europe) – includes "Bubo" poirreiri
  • Intulula (Early/Middle Miocene of WC Europe) – includes "Strix/Ninox" brevis
  • Alasio (Middle Miocene of Vieux-Collonges, France) – includes "Strix" collongensis

Placement unresolved:

  • "Otus/Strix" wintershofensis – fossil (Early/Middle Miocene of Wintershof West, Germany) – may be close to extant genus Ninox[7]
  • "Strix" edwardsi – fossil (Middle Miocene of Grive-Saint-Alban, France)
  • "Asio" pygmaeus – fossil (Early Pliocene of Odessa, Ukraine)
  • Strigidae gen. et sp. indet. UMMP V31030 (Rexroad Late Pliocene of Kansas, USA) – Strix/Bubo?[8]
  • Ibiza owl, Strigidae gen. et sp. indet. – prehistoric (Late Pleistocene/Holocene of Es Pouàs, Ibiza)[9]

The supposed fossil heron "Ardea" lignitum (Late Pliocene of Germany) was apparently a strigid owl, possibly close to Bubo.[10] 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.

References

  1. 1 2 Marks, J. S.; Cannings, R.J. and Mikkola, H. (1999). "Family Strigidae (Typical Owls)". In del Hoyo, J.; Elliot, A. & Sargatal, J. (eds.) (1999). Handbook of the Birds of the World. Volume 5: Barn-Owls to Hummingbirds. Lynx Edicions. ISBN 84-87334-25-3
  2. ↑ Earhart, Caroline M. & Johnson, Ned K. (1970). "Size Dimorphism and Food Habits of North American Owls". Condor. 72 (3): 251–264. doi:10.2307/1366002.
  3. ↑ Kelso L & Kelso E (1936). "The Relation of Feathering of Feet of American Owls to Humidity of Environment and to Life Zones". Auk. 53 (1): 51–56. doi:10.2307/4077355.
  4. ↑ Geggel, Laura (September 19, 2016). "Are All Owls Actually Night Owls?".
  5. ↑ Leach, William Elford (1820). "Eleventh Room". Synopsis of the Contents of the British Museum (17th ed.). London: British Museum. pp. 65–70. OCLC 6213801. Although the name of the author is not specified in the document, Leach was the Keeper of Zoology at the time.
  6. ↑ Bock, Walter J. (1994). History and Nomenclature of Avian Family-Group Names. Bulletin of the American Museum of Natural History. Number 222. New York: American Museum of Natural History. p. 142.
  7. ↑ Olson, p. 131
  8. ↑ Feduccia, J. Alan; Ford, Norman L. (1970). "Some birds of prey from the Upper Pliocene of Kansas" (PDF). Auk. 87 (4): 795–797. doi:10.2307/4083714.
  9. ↑ Sánchez Marco, Antonio (2004). "Avian zoogeographical patterns during the Quaternary in the Mediterranean region and paleoclimatic interpretation" (PDF). Ardeola. 51 (1): 91–132.
  10. ↑ Olson, p. 167

Bibliography

  • Olson, Storrs L. (1985). The fossil record of birds. In: Farner, D.S.; King, J.R. & Parkes, Kenneth C. (eds.): Avian Biology 8: 79–238. Academic Press, New York.
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