TAWNY OWL

Strix aluco

English: Tawny Owl.
German: Waldkauz.
French: Chouette hulotte.

Clasificación/Clasification

Order: Strigiformes.
Family: Strigidae.

Longitud/Length

37-43 cm.

Envergadura/Wingspan

81-96 cm.

Aves relacionadas/Similar species

The Tawny Owl cannot be confused with any other Iberian nocturnal bird of prey as it is the only one with gray or reddish tones and completely dark eyes.

Sexo/Sexing

The feathers are very similar in both males and females, so it is not a variable to consider when sexing this species. Due to the overlap in size, it is also not a variable to consider for this purpose.

Edad/Ageing

It is possible to recognize 5 different ages:

Juvenile specimen: these individuals have a single generation of feathers, both in flight feathers and tail feathers. The primary coverts have two or three narrow dark bars. The primaries are narrow and with a sharp tip. The primaries and secondaries also have the narrowest dark subterminal bar and it usually tends to be incomplete. The tail feathers are slightly pointed, with one end in white-gray tones with light (or nonexistent) dark speckling.

2nd year / 3rd year specimen: they have two generations of feathers on the wing. Some internal primaries and some external secondaries are new and show an adult design. The rest show a juvenile design with a subtle wear. All the tail feathers already have the adult specimen pattern.

3rd year / 4th year specimen: these individuals have some un-molted juvenile secondaries (retained) but at the same time have two generations of primaries with an adult pattern.

4th year / 5th year specimen: this stage is only recognizable in individuals that have some retained juvenile secondaries but the rest of the feathers are of adult type.

Adult specimen: it is easy to find these specimens with two or more generations of flight feathers, but all with an adult pattern. The primary coverts have no more than two wide dark bars. The primaries have a wide tip and like the secondaries, have the dark subterminal bar with the same width as the rest (usually complete). The tail feathers have a rounded tip and bathed in gray tones with dark speckling, although wear and individual variation can make it difficult to appreciate the design of the tip.

Muda/Moult

The Tawny Owl performs almost complete post-nuptial molt, which usually ends in November, but not all flight feathers are changed each year.

On the other hand, the post-juvenile molt is a partial process that includes body feathers and medium and small secondary coverts, with the large secondary coverts, primaries, secondaries, and tail feathers excluded. In the 2nd year, the molt includes all the tail feathers, some internal primaries (usually two or three), and generally the two innermost tertials, with the rest of the juvenile flight feathers being retained. In the 3rd year, all the primaries and most of the juvenile secondaries that had been retained are molted.

Some specimens may retain some juvenile secondaries for one more year.

Configuración del plumaje/Plumage configuration

Primaries: 10 per wing.
Secundaries: 15 per wing.
Rectrices: 12.

Observaciones/Remarks

Link: http://blascozumeta.com/

La obtención de este material ha sido posible gracias al permiso necesario de la Junta de Andalucía.

AUTORIZACIÓN DE LA DIRECTORA GENERAL DE MEDIO NATURAL, BIODIVERSIDAD Y ESPACIOS PROTEGIDOS DE LA CONSEJERÍA DE AGRICULTURA, GANADERÍA, PESCA Y DESARROLLO SOSTENIBLE DE LA JUNTA DE ANDALUCÍA, PARA LA CESIÓN DE MUESTRAS BIOLÓGICAS DE ESPECIES DE FAUNA (ARTÍCULO 9 DE LA LEY 8/2003, DE 28 DE OCTUBRE, DE LA FLORA Y LA FAUNA SILVESTRES).

Medidas/Measures

Biometría/Biometrics

Adult specimen:
Beak tip to pupil center:
Tarsus:

Juvenile specimen

1.- Right wing primaries. 2.- Primaries. 3.- Details of the tip of the primaries. 4.- Details of the barrel of the primaries. 5.- Details of the outer vane of the outer primaries. 6.- Details of P10 and P9. 7.- Details of P8. 8.- Details of the outer vane of the primaries. 9.- Details of the outer and inner vanes of P8. 10.- Secondaries S1-S7. 11.- Secondaries S8-S14. 12.- Right wing secondaries and tertials. 13.- Details of the tip and outer vane of the central secondaries. 14.- Details of the tip and outer vane of the secondaries and tertials. 15.- Details of the calamus of the secondaries and tertials. 16.- Right wing tertials. 17.- Details of the tertials. 18.- Details of the outer and inner vanes of the secondaries (S8-S9). 19.- Details of the tip of S8-S9. 20.- Primaries, secondaries, and tertials of the right wing. 21.- Primaries, secondaries, and tertials of the right wing. 22.- Primaries, secondaries, and tertials. Greater coverts and primary coverts. 23.- Primaries, secondaries, and tertials. Greater coverts and primary coverts + median coverts. 24.- Primaries, secondaries, tertials. Primary coverts and secondaries coverts (G, M, and L). Alulas. 25.- Primary coverts. 26.- Details of the primary coverts. 27.- Details of the greater coverts. 28.- Details of the secondary coverts (G, M, and L). 29.- Details of the median coverts. 30.- Details of the secondary coverts. 31.- Details of the secondary coverts. 32.- Primary coverts. 33.- Greater coverts. 34.- Alulas. 35.- Rectrices. 36.- Rectrices. 37.- Rectrices + uppertail coverts. 38.- Details of the uppertail coverts. 39.- Uppertail coverts. 40.- Details of the tip of the rectrices. 41.- Details of R1. 42.- Details of R1. 43.- Rectrices + undertail coverts. 44.- Details of the undertail coverts. 45.- Undertail coverts. 46.- Assembly of the right scapula. 47.- Scapula feathers. 48.- Assembly of the right flank. 49.- Flank feathers. 50.- Primary infra-coverts. 51.- Secondary infra-coverts. 52.- Assembly of the chest. 53.- Chest feathers. 54.- Belly feathers. 55.- Right leg feathers. 56.- Back feathers. 57.- Ear feathers. 58.- Details of the ear feathers. 59.- Crown feathers. 60.- Sensory feathers on the face and beak.

TAWNY OWL

Medidas/Measures

Juvenile specimen

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