The male song of the Javan silvery gibbon (Hylobates moloch)

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6 T. Geissmann et al. – The Male Song of the Javan Silvery Gibbonfined and described below. Duration andfrequency measurements were taken on threerepresentative notes of each note type per individual.Summary measurements (mean, standarddeviation, range) are presented in Table 2. Inaddition, the table lists the number of gibbons andthe number of notes that were available for themeasurements. Because not all individuals useevery note type in their song bouts, the number ofindividuals studied may differ between note typesin the table. Typical sonagrams of all note typesand classes are shown in Figure 2.Based on their different mechanisms ofutterance, we first differentiate between expirationnotes and inspiration notes (i.e. notes which areproduced during exhalation and during breathintake, respectively). As there is no intermediateoption between these two forms of vocalisation,the two forms cannot, by definition, grade intoeach other and are, therefore, identified as twodifferent note classes. Expiration notes representthe large majority of the song repertoire.Expiration notes can be further divided in anumber of note types. They represent a gradedsystem, and intermediate forms can be foundamong the different types. Yet, because someforms are particularly common, we identifiedthem as different note types, although thesedivisions remain arbitrary. Based on similarity,expiration note types are combined into four basicgroups: oo notes (1 type), wa notes (4 types),chevron notes (7 types) and variable notes (1type). Only one type of inspiration note isrecognised in this study.Oo notesThe oo notes (Type A) are the most simple expirationnotes in the male song repertoire, exhibitingthe lowest intensity, the shortest duration (0.2±0.1s) and the smallest amount of frequencymodulation (Figure 2). The fundamental frequencyis below 1 kHz. Oo notes exhibit only amoderate amount of frequency modulation, butthe note shape in the sonagram is very variable:We found oo notes of increasing, decreasing orstable frequency. More complex sonagramstructures – such as u-shaped or n-shaped notes ornotes which begin with stable frequency butsharply go down at the end of the note – alsooccur. Oo notes are preferentially uttered at thebeginning of the male song bout, but also occurduring mild disturbances and moderate excitementoutside of the song context.During song bouts, notes may gradually changefrom oo notes into wa notes (see below).Wa notesFollowing Kappeler (1984a), the most commongroup of expiration notes are termed wa notes.They are short like, but louder than, oo notes andcharacterised by a fast frequency increase. Startingfrequency and minimum frequency alwayscoincide in wa notes. After reaching the maximumfrequency near the end of the note, a terminalfrequency decrease is absent or slight, amountingto less than half of the preceding frequencyincrease. Wa notes are very variable in their endand maximum frequencies. We distinguish betweenfour different note types (Figures 2), whichwe term B1, B2, B3 and B4 in the following text.Note type B1 comprises wa notes of relativelymoderate frequency modulation. Notes have astarting frequency of about 0.7 kHz or below, andreach a maximum frequency of 1 kHz or less.Note type B2 resembles B1, but the maximumfrequency ranges from above 1 kHz up to 1.3 kHz.Note type B3 comprises the wa notes with thehighest amount of frequency modulation. Thisnote type resembles B1, but the maximumfrequency ranges from above 1.3 kHz to about 1.5kHz. Note type B4 includes wa notes with arelatively high starting frequency (i.e. above 0.7kHz). The maximum frequency is variable and canrise to about 1.5 kHz.The trill is a particularly stereotyped figure (i.e.a song unit intermediate between single notes andphrases). Trills are short bursts of three to five B1notes with very short intervals. Often, the trillexhibits a distinct decrease in minimum frequency,maximum frequency and frequency rangefrom the first to the last trill note. Individual trillnotes may or may not be followed by inspirationnotes (described below). Trills usually are precededby a B2 or B3 note, also with facultativeinspiration note.Chevron notesThe third group of note types comprises thosenotes which have been termed wa-oo and wa-oowanotes by Kappeler (1984 a) and are referred toas chevron notes in the present study. Allchevrons begin with rising frequency, then, afterreaching a peak, frequency decreases again.Chevron notes differ in their frequency structure
Contributions to Zoology, 74 (1/2) – 2005 7and duration. Based on their shape in thesonagram, some chevron notes exhibit two distinctparts. The first part of the note (a) consists of thechevron proper described above. The second part(b) is the drawn-out tail of the chevron (Figure 1).The tail’s frequency structure is particularlyvariable. Chevron notes are introduced relativelylate during the song bout, after the wa notes.Chevron notes represent the most characteristicvocalisations in the song of male silvery gibbons,but are absent or very rare in female song bouts.Individual males appear to differ strongly in theiruse of chevron notes in general and of certaintypes of chevron notes in particular. Wedifferentiate between seven types of chevron notesin H. moloch (Figure 2), which we term C1, C2,C3 and so on in the following text.Note type C1 is of a simple chevron form in thesonagram; a tail end is absent. This note typereaches a maximum frequency of 1 kHz or less.Note type C2 resembles C1, but its maximumfrequency is situated above 1 kHz. Note type C3 isa chevron with a tail end. The latter is of chevronform, too, with its own peak frequency. After thetail peak, the frequency descends to about thestarting level for the second time. Note type C4resembles C3, but the frequency remains nearlyunmodulated in the tail end. Note type C5 also is achevron with a tail end. After reaching the firstpeak of the chevron, the frequency descends onlymoderately and does not reach the level of thestarting frequency. In the tail end, the frequencyrises again and reaches or even surpasses themaximum frequency of the first peak. Note typeC6 resembles C5, but the frequency rise in the tailend is more moderate and does not reach themaximum frequency of the first peak. Note typeC7 is a simple chevron resembling C2, but thefrequency decrease occurs much more slowly thanthe initial increase.Variable notesThe fourth group is termed variable notes andincludes only one note type, D. It comprises allexpiration notes which are neither wa notes norchevron notes. Notes of this type are extremelyvariable (Figure 2). Further partitioning of thisgroup would easily be possible but was not founduseful considering its rarity in the song bout.Variable notes are long (0.6±0.2 s) and of verymoderate frequency modulation (0.3 kHz or less).The direction of the frequency modulation isvariable; the frequency may rise, drop or changerepeatedly.The variable figure (Figure 2) is not a singlenote, but a cluster of more than three notes, withextremely short intervals and with a total durationof 1.5±0.3 s. All note types of the male songrepertoire may occur in these rapid notesequences, but variable notes and inspiration notesare most prominent. Both the degree and thedirection of frequency modulations are veryvariable in these figures. Intervals may be so shortthat the number of individual notes uttered in aseries can sometimes not be determined reliably.Therefore, variable figures were not broken downinto single notes for the note counts of this study(see below) but simply recorded as one unit.Inspiration notesThis note class also is variable in its frequencystructure, but most commonly exhibits an eitherdecreasing or chevron shape. Despite thestructural variability of inspiration notes, only onetype is recognised here (type E). A furtherpartitioning of this class did not appear to beuseful because of its rarity. Often, an inspirationnote immediately follows a wa note (forming a socalledwa-aa figure), or appears to link twoexpiration notes together (forming a wa-aa-wafigure). In these figures, intervals between notesare very short (the second sonagram of an E notein Figure 2 shows a typical wa-aa-wa figure).Particularly fast alternations of B1 and E notes canoccur in trill figures (described above). Inspirationnotes are often less loud than the accompanyingwa notes. The so-called variable figures (seeabove) may also include inspiration notes.Individuality in the note repertoireNot all note types were used by all males (at leastnot in the song material available for this study),as listed in Table 3. For instance, the Howletts 2male was lacking types C4 and C5, Howletts 3was lacking C3, C4, C5, and C6, and the songbout of the Halimun male did not include notetype D. Similarly, the variable figure did not occurin the song of the Howletts 3 and Halimun males.Trill figures were even less common. As a regularcomponent of the song repertoire, they onlyoccurred in the song of the Jakarta 2 male. They
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The male song of the Javan silvery gibbon (Hylobates moloch)

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