Duetting Scops Owls

Earlier this month I was birding in Extremadura in western Spain, camping on the edge of Monfragüe National Park. Each morning I woke to the sounds of Hoopoes and Iberian (Azure-winged) Magpies. In the evening after sunset, Eurasian Scops Owls (Otus scops) began 'singing' and one evening I managed to locate a bird about 600 metres away on the road to Malpartida de Plasencia. 

Dehesa habitat around Monfragüe

What was most interesting was that from a distance it sounded like a single bird, but on getting closer it didn't sound like a typical Scops Owl. In fact, what I was hearing was both a male and female in perfect, overlapping synchronisation. Have a listen to the sound recordings below (and click the sonograms for a larger image). The male is producing the lower frequency sound at 1.23-1.94 kHz, with the female at 1.41-1.61 kHz.

Duetting pair with almost perfect synchronisation; the female is producing the second, quieter, shorter and higher-pitched part.

Detail from the above sonogram showing the duet detail: Male song in blue Female song in red

At times the female would drop out of the duet, and the sound clip and sonogram below shows the male vocalising alone. It appeared to produce a slightly longer note when not duetting.

Song/territorial call from the male.