Résumé
Recent studies on mate-quality recognition in passerines showed that females use subtle differences in sound production to assess males. We analysed long calls of brown skuas,
Catharacta antarctica lonnbergi, to test whether vocal performance could serve as an indicator of individual quality in a nonpasserine species. Measurements of vocal performances focused on two acoustic parameters for which motor constraints have been reported in passerines, namely ‘vocal deviation’ and ‘peak performance’. As potential indicators of individual quality we measured body size, body condition (body mass corrected for size) and mean reproductive success. We found a triangular distribution of calls between note repetition rate and frequency bandwidth. Males performing long calls closer to the performance limit had a higher mean reproductive success than males that show long calls with a larger vocal deviation. Similarly, males calling with a high peak performance were more successful breeders than males with low peak performance. Our findings indicate that long calls of brown skuas are limited by motor constraints similar to vocalizations in passerines. We show that differences in vocal performance reflect male's reproductive success with more successful breeders producing the more difficult calls. This implies that limits on vocal performance due to motor constraints present a suitable mechanism for mate-quality recognition in nonpasserine birds.