Distinctiveness in the territorial calls of great horned owls within and among years

Many animals have vocalizations that are individually distinguishable. Researchers can use these differences to facilitate monitoring of individuals. To be an effective monitoring tool, vocalizations must be recognizable throughout a season and preferably throughout an animal's lifetime. We assessed whether the territorial calls of Great Horned Owls (Bubo virginianus) are individually distinct, both within a season and over several years. Both males and females could be readily identified by their territorial calls. Based on a comparison of within-to between-individual coefficients of variation and a multivariate analysis of variance (MANOVA), nearly all vocal characteristics we measured carried individually distinct information. Using forward stepwise discriminant function analysis (DFA), we found that the internote interval between the last short and first long note of the call was the most useful for identifying both individual males and females. The duration and minimum and maximum frequency of long notes were important for discriminating among individual males whereas the number of notes and total call duration were important characteristics for identifying individual females. Using cross-validation DFA, both male and female Great Horned Owls were accurately assigned to location both throughout a season and among years. Correct assignment of males was reduced across recording sessions and among years compared to within a recording session, but was still greater than expected by chance. Together, our results suggest that individually distinct vocalizations could be an effective tool for identification of Great Horned Owls for long-term monitoring.