Indicators of male quality in the hoots of Tawny Owls (Strix aluco)

The number of songs in a male's repertoire, and the amount of time he spends singing, have been shown to correlate with territory size and quality, reproductive success, parental care and parasite load in some passerine species. In addition, females of some species use song rate and complexity as a cue to mate choice and are more responsive to more frequent and complex songs. Few studies, however, have examined the influence of body size and parasitic infections on the sound frequency (pitch) and structure of vocalizations of birds. The Tawny Owl (Strix aluco) hoot is important in communication between birds at night when visual information is limited, and is simple enough to allow a quantitative analysis of its structure. Six temporal and four frequency measures of the hoots of 50 Tawny Owls were taken, and compared to body mass, wing length, breeding success and number and intensity of parasitic infections of the singers. There was a decrease in call frequency with increasing body mass and the vibrate tail of the last note was longer in larger birds, but there was no part of the call that correlated with breeding success. There was an increase in call frequency as the number of parasitic infections increased, and there was a decrease in the length of calls as the intensity of parasitic infections increased.