Repertoire, structure, and individual distinctiveness of Thick-billed Murre calls

We describe the vocal repertoires of Thick-billed Murre (Uria lomvia) adult s and chicks during the breeding season. Using recordings from throughout t he chick-rearing period, we identified four distinct calls of chicks and si x of adults. We present sonograms and quantitative descriptions of each cal l and summarize the behavioral context in which they were used. Chick calls are mostly flute-like sounds at approximately the same pitch that tend to develop from a simple peep during hatching through a rapidly frequency-modu lated departure call, given shortly before, during, and after they leave th e colony at fledging. Departure calls appear to facilitate interactions bet ween the chick and the attending male parent during this risky period for t he chick. Adult calls are lower pitched and sound more gruff, with differen t call types having significantly different pitch, duration, and number of syllables. Among-individual variation in the crow calls of adults accounts for 44% of the measured variation in this call and indicates the potential for individual recognition, such as the recognition of parents' calls by th eir chicks, which we have previously documented. Temporal features may form the basis of recognition of adult calls in this species, given that they a ccounted for twice as much variation as frequency features among individual adults.