[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).

[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.

A large group of pigments defined by nitrogen-containing pyrole rings, including chlorophyll and heme (in animal blood), make up the porphyrins.

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.

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.

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.

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.

[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.

Owls avoid badly burned areas but they benefit from the mosaics of heterogeneous habitats created by fires.

[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.

[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).

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