Individual Identification of Male Ural Owls Based on Territorial Calls

Effective individual identification is important in many aspects of animal studies. Leg bands and wing tags are commonly used to mark individual birds in the field; however, for nocturnal or cryptic birds it is difficult to directly observe individual tags due to darkness or dense vegetation. Alternatively, some studies suggest that many birds have individually distinctive vocalizations, and these differences could be used to identify individuals. Here we assessed the possibility of identifying individual Ural Owls (Strix uralensis) based on their defensive territorial hooting calls. During breeding season, we recorded hooting calls of 15 males in 2018 and of 16 males in 2019 respectively at the Dagangzi national forest in northeastern China. We measured 19 variables for each call. Using forward stepwise discriminant function analysis, we correctly classified 92.8% of the calls of individuals in 2018 and 93.9% in 2019, based on leave-one-out cross validation. The most important discriminating variables included duration of the interval between the first and second notes, duration of the interval between the second and third notes, the third note duration, and the number of "humps" (upward projections in a note in the sound spectrogram) in the first note. The calls of individuals remained stable both within a breeding season and between years. Our results suggest that territorial calls are effective for identifying male Ural Owl individuals, and this technique could contribute to population surveys and long-tenn monitoring.