Variation in call properties of the snow petrel, Pagodroma nivea, in relation to sex and body size

We studied the physical parameters of calls of the snow petrel, Pagodroma n ivea, in relation to body size, sex and individual specificity. Frequency p arameters were related to body size in both males and females; larger indiv iduals' voices were pitched approximate to 2 kHz lower than those of smalle r individuals. Males' voices were pitched, on average, 376 Hz lower than th ose of females but the relation between frequency parameters and body size was similar in males and females. The rhythm of the call was sex-specific, the intersyllabic duration being shorter in females than in males. The vari ables most specific to individuals were those relating to frequency paramet ers, duration of the call and temporal patterning. The relationship between body size and frequency parameters, together with the high degree of geogr aphic variation found in this species, suggest that care should be taken wh en analysing geographic variation in bird calls.