| Summary: | Bird vocalizations are critical cues in social interactions as they convey temporary information varying with the social context, e.g. the signaler motivation when facing a rival or a potential mate. To date, literature mainly focuses on learning birds. Burrowing petrels (Procellariidae) are non-learning birds with a limited vocal repertoire. Bachelor males communicate with conspecifics with a single call emitted in three situations: in absence of a certain auditory (spontaneous calls), towards females (female-directed calls) and toward males (male-directed calls). We first hypothesized that, although the call structure is preserved, temporal and spectral parameters vary between the three call types of bachelor males, translating different motivations (Motivation Hypothesis). To go further, we hypothesized that acoustic variations in male-directed calls indicate the signaler's aggressive motivation and therefore the variations are similar whether calls are produced by breeder or bachelor males (Breeding-Status Hypothesis). We tested the two hypotheses performing field playback experiments on two petrel species: the blue petrel (Halobaena caerulea) and the Antarctic prion (Pachyptila desolata). Despite the obvious call stereotypy, we observed temporal variations and frequency shifts when males react to a female or a male, which may translate the sexual or aggressive motivation of the signaler. Furthermore, the similarity of variations in male-directed calls of both breeder and bachelor males suggests the aggressive motivation. So far, vocal plasticity in non-learning birds have been greatly underestimated. Here, we highlighted the expression of different motivations through vocal variations and the ability to produce frequency variations in species with genetically coded vocalizations. Abbreviations and explanations of the dataset variables: Species Recorded species (0= Antarctic prion; 1=blue petrel) A.F0 Fundamental frequency of A syllable A.Q25 A upper quartile (frequency at the upper limit of the 25% energy ...
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