DOI: 10.5061/dryad.8sf7m0cmj
title: Contextual variations in calls of two non-oscine birds: the blue petrel and the Antarctic prion

description: 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.
description: To compare the acoustic
 structure of male calls according to the social situation and to their
 breeding status, we recorded the three call types (spontaneous,
 female-directed, and male-directed) from males of two burrowing petrel
 species, the blue petrel <em>Halobaena caerulea </em>and the
 Antarctic prion <em>Pachyptila desolata</em>. Records were
 made using field playback experiments on a small sub-Antarctic island
 within the Kerguelen Archipelaguo (Ile Verte, 49°51′ S, 70°05′ E) during
 the birds' breeding season in 2013, 2017, 2018. In total, we obtained
 N = 678 phrases of blue petrels (117 on breeders and 561 on bachelors) and
 428 phrases of Antarctic prions (71 on breeders and 357 on
 bachelors).  To describe and compare the call structure, we measured
 34 acoustic parameters in both temporal and spectral domains at two
 syntactic levels (syllables and phrases) on recorded calls using the
 software Avisoft-SASLab Pro v5.2.11. To increase the accuracy of frequency
 measurements, we preliminarily downsampled recorded calls from 44.1 to
 11.025 kHz using the automatic “Sampling Frequency Conversion”
 functionality of Avisoft. We also high-passed filtered (cutting frequency:
 0.10 kHz, FFT filter) recorded calls to remove low-frequency background
 noise, which does not affect recordings. We counted the number of
 syllables and phrases on sonograms. We did not analyze syllables C2 to Cn
 as they are not present in all individuals. We automatically extracted
 temporal variables on the amplitude envelopes using the software
 functionality “Pulse Train Analysis”, with a resolution of 11.6 ms. This
 functionality automatically measures the temporal structure of waveforms
 using pulse recognition algorithms. We automatically extracted fundamental
 frequencies and variables describing energy spectral distribution on
 linear amplitude spectrum with a resolution of 22 Hz. Automatic
 extractions were based on similar pre-sets for all birds to ensure
 replicable measurements.
description: <strong>Abbreviations and explanations of the dataset variables:</strong> 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 of A syllable) A.Q50 A medium quartile (frequency at the upper limit of the 50% energy of A syllable) A.Q75 A lower quartile (frequency at the upper limit of the 75% energy of A syllable) B.F0 Fundamental frequency of B syllable B.Q25 B upper quartile B.Q50 B medium quartile B.Q75 B lower quartile C1.F0 Fundamental frequency of C syllable C1.Q25 C1 upper quartile C1.Q50 C1 medium quartile C1.Q75 C1 lower quartile D.F0 Fundamental frequency of D syllable D.Q25 D upper quartile D.Q50 D medium quartile D.Q75 D lower quartile Ph.F0 Mean fundamental frequency of the phrase Ph.Q25 Phrase upper quartile Ph.Q50 Phrase medium quartile Ph.Q75 Phrase lower quartile A.Du A syllable duration B.Du B syllable duration C1.Du Duration of the first syllable C D.Du D syllable duration B.Int Inter-syllable A-B duration C1.Int Inter-syllable B-C1 duration D.Int Inter-syllable C1-D duration Ph.Du Phrase duration Syll.Tempo Number of syllables per seconds for each phrase Ph.Tempo Number of phrase per second for each call Ph.Rhythm Ratio between syllable and silence durations Call.NbPh Number of phrases in a call Ph.NbSyll Number of syllables in a phrase CallType Call type (0=spontaneous; 1=male-directed; 2=female-directed) BreedingStatus Breeding status of the recorded male (0=bachelor; 1=breeder) CallCode Code of the recorded calls PhCode Code of the recording phrase Individual Code or ring number of the recorded male