Previous studies in seabirds have shown that the confusing environment of reproductive colonies constrains acoustic communication between sexual partners and between parents and offspring. Although between-species comparison of coding strategies helps determining convergences driven by this external constraint, it would now be interesting to compare strategies used by both sexes within a given species, especially when sexual dimorphism of acoustic signals is marked. The blue-footed booby Sula nebouxii is a socially monogamous seabird living in tropical and sub-tropical areas of the East Pacific ocean. Individuals come to shore only for breeding, forming large colonies of reproductive pairs. During the nest and young attendance period, sexual partners alternate stays at the nest with foraging trips at sea. During roles exchange, vocal interactions may support mate recognition. Working on the colony established on Isla Isabel (Nayarit, México), we (1) recorded calls of adults, (2) did an acoustic analysis in search of potential individual signatures using semi-automatic measurements (SEAWAVE software), and (3) tested the efficiency of vocal individual recognition by playback experiments. The female call is an amplitude-modulated sound, showing harmonic series slowly modulated in frequency, with heterogeneous distribution of energy among the spectrum. The male call sounds like a noisy whistle strongly modulated in frequency. In spite of their strong dimorphism, both calls support individual identity with different acoustic features encoding the signature. Playback experiments showed that individual vocal recognition does exist. However, we will discuss the presence of recognition errors that questions the reliability of the acoustic recognition system in the absence of visual cues.
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