Representative spectrogram showing the parameters measured: Start F (frequency at call onset), End F (frequency at call offset), Delay; Number of syllables (black number = syllable mother, red number = syllable juvenile male) and song organization of mother’s (M) and juvenile’s (J) “great calls”.

<p>Dashed line represents notes of juvenile’s “great call”: N(J)–note juvenile, T(J)–“twitter” juvenile; solid line represents notes of mother’s “great call”: O–“oo” notes, B–“bark” notes, T–“twitter”.</p

The traits of the great calls in the juvenile and adolescent gibbon males <i>Nomascus gabriellae</i>

<div><p>Knowledge about vocal ontogeny and vocal plasticity during ontogeny in primate species is central to understanding the evolution of human speech. Vocalizations in gibbons (<i>Hominoidea</i>) are very interesting and contain complex species- and sex-specific patterns. However, ontogeny of gibbon songs is little studied. Here, we document regular production and ontogenetic changes of female-specific “great call” in 4 immature (2 juvenile—c.a. 3 years old; and 2 adolescent—c.a. 5 years old) males of southern yellow-cheeked gibbon (<i>N</i>. <i>gabriellae</i>) over nine months. None of the males produced fully developed adult-like “great call” and little ontogenetic changes to “great calls” occurred. “Great calls” of sons were shorter, started higher and ended lower than those of their mothers. Regular production of twitter part of great call likely appears around 4^th year as it was observed in adolescent but not in juvenile males.</p></div

Predicted values of the delay in temporal synchrony of great calls emitted by an adult female and her son plotted against log-transformed age of the son.

<p>Predicted values of the delay in temporal synchrony of great calls emitted by an adult female and her son plotted against log-transformed age of the son.</p

Information about subjects.

<p>Information about subjects.</p

Logit of a “twitter” occurrence in the “great call” of the son plotted against log-transformed age of the juvenile or adolescent son.

<p>Logit of a “twitter” occurrence in the “great call” of the son plotted against log-transformed age of the juvenile or adolescent son.</p

Typical male’s (left) and female’s (right) spectrogram showing the vocalization of southern yellow-chekeed gibbons.

<p>Typical male’s (left) and female’s (right) spectrogram showing the vocalization of southern yellow-chekeed gibbons.</p

Differences in characteristics of adult female´s and their son´s “great calls” (least squares mean ± SE).

<p>A) start frequency of the first syllable, B) start frequency of the last syllable, and C) number of syllables preceding the”twitter”.</p

Daily intake of experimental diets fed to chimpanzees (means of wet matter, g/day and chimpanzee).

<p>HSD – high starch diet; LoSD – low starch diet. ¹Zoo Hodonín: orange, grapes, apple, pineapple, banana, kiwi, pears, watermelon, plum, nectarine; ¹Zoo Brno: orange, grapes, apple, pineapple, banana, kiwi; ²both zoos: pepper, tomato, carrot, kohlrabi, cucumber; ³Zoo Hodonín: onion, leek, cauliflower, beet, spring onion, lettuce, Chinese leaves, nectarine; ³Zoo Brno: onion, leek, cauliflower, beet, lettuce, Chinese leaves.</p

Numbers of <i>Neobalantidium coli</i> in chimpanzee feces during low-starch (LoSD) and high-starch (HSD) diets in two study groups.

<p>Numbers of <i>Neobalantidium coli</i> in chimpanzee feces during low-starch (LoSD) and high-starch (HSD) diets in two study groups.</p