The true owls or typical owls (family Strigidae) are one of the two generally accepted families of owls, the other being the barn owls and bay owls (Tytonidae). This large family comprises 230 living or recently extinct species in 23 genera. The Strigidae owls have a cosmopolitan distribution and are found on every continent except Antarctica.
Morphology
thumb|right|upright|Cross sectioned [[great grey owl specimen showing the extent of the body plumage, Zoological Museum, Copenhagen]]
thumb|upright|Skeleton of a Strigidae owl
Typical owls (hereafter referred to simply as owls) generally share an extremely similar body plan, though they 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. 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. 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. 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. The toes and tarsi are feathered in some species, and more so in species at higher latitudes. 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.
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.
Niche competition
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 are now 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.
Communication
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.
Migration
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.
Habitat, climate and seasonal changes
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 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.
Predators
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.
Systematics
thumb|[[Spectacled owl (Pulsatrix perspicillata)]]
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.
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. 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).
The cladogram below is based on the results of the study by Salter and collaborators published in 2020. A genetic study published in 2021 suggested that the genus Scotopelia may be embedded within Ketupa.
thumb|[[Blakiston's fish owl (Ketupa blakistoni) the largest species of owl]]
thumb|upright|[[Tawny owl (Strix aluco)]]
The 235 extant or recently extinct species are assigned to 23 genera:
- Alasio (Middle Miocene of Vieux-Collonges, France) – includes "Strix" collongensis<!-- Olson1985:131 -->
The fossil database for Strigiformes is highly diverse and shows an origin from ~60 Mya into the Pleistocene. The maximum age range for the Strigiformes clade extends to 68.6 Mya.
Placement unresolved:
- "Otus/Strix" wintershofensis – fossil (Early/Middle Miocene of Wintershof West, Germany) – may be close to extant genus Ninox
- "Strix" edwardsi – fossil (Middle Miocene of Grive-Saint-Alban, France)
- "Asio" pygmaeus – fossil (Early Pliocene of Odesa, Ukraine)
- Strigidae gen. et sp. indet. UMMP V31030 (Rexroad Late Pliocene of Kansas, US) – Strix/Bubo? 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==<!-- Emu102:223 -->
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.
External links
- ITIS – Strigidae Taxonomy
- Typical owl videos on the Internet Bird Collection
- The Owl Pages about owls – photos, calls, books, art, mythology and more.