ABSTRACT
For species maintaining long-term social bonds, particularly in complex networks such as dense colonies, vocal cues to identity can be crucial. Here, we investigated the vocal individuality within and across five call types of the little auk: a monogamous, colonial bird with a strong nest fidelity. Calls produced inside the nest over the incubation period were recorded in 2019 and 2020 and assigned to a call type and individual. We extracted a set of 16 acoustic parameters for each vocalization, and seven additional temporal patterns for a complex, multisyllable call. Calls could be reliably assigned to an individual both within and across call types, although classification performance differed between linear and machine learning methods. All call types showed information content theoretically allowing us to distinguish at least 11 individuals, and up to at least 41 for the classic call. The raw acoustic parameters that contributed most information across the five call types (i.e. the five highest potential of individuality coding scores) were peak fundamental frequency, frequency value at the upper limit of the second and first quartiles of energy, sound duration and amplitude modulation rate. We suggest that this strong individuality across call types and parameters is selected for in the species to help maintain monogamous partnerships, and perhaps social bonds with neighbours, over the years.
