Although early nocturnal raptors were considered close to day raptors(eagles, hawks …), later studies have shown greater similarity with nightjars and other nocturnal birds (podargos, nictibios, egotelos, etc.).

Based on DNA studies, some authors have come to group these strange birds and nocturnal raptors in the order Strigiformes, although later studies advised to maintain the traditional separation between them.

The classification by the definitive moment, and therefore more commonly used is the following:

N. Comonn	N. Scientific	Order	Family
Eagle owl	Bubo bubo	Strigidae	Strigiforme
Tawny owl	Strix aluco	Strigidae	Strigiforme
Long-eared owl	Asio otus	Strigidae	Strigiforme
Short-eared owl	Asio flammeus	Strigidae	Strigiforme
Llittle owl	Athene noctua	Strigidae	Strigiforme
Scops owl	Otus scops	Strigidae	Strigiforme
Boreal owl	Aegolius funereus	Strigidae	Strigiforme
Barn owl	Tyto alba	Tytonidae (lechuzas)	Strigiforme

The differences between the two families are clear and are based on morphological characters, such as the following:

Caracter	Strigidae	Tytonidae
Skull	Rounded	Elongated
Orbits	Big	Small
Beak	Short, curvy and width	Long, straight and stretch
Notches at the posterior border of sternum	Two pairs of recesses	Two recesses
Tarsus-metatarsus	Short	Long
Ears	Symmetrical in shape and size, but left higher than right.	Often asymmetrical in size / shape (right is larger)
Furcula	Pneumatic	Not Pneumatic
Sawing on the nail of the middle finger	Smooth	Sawed
2nd and 3rd finger	3rd larger 2nd	Same size
Eggs	Rounded	Elongated

Taxonomic comparison of Owl Royal (left) and Barn Owl (right).