Knowledge of the ontogeny and development of vocalization in primates play a crucial role in understanding the evolution of the human language. Unlike the great apes, gibbons produce a remarkable vocal performance, which includes complex species- and sex-specific patterns. Many studies in the past focused on research of the acoustic pattern in adult individuals. Yet, it remains unclear how the males develop their sex-specific pattern of vocalization. This dissertation focuses on two specific periods in the ontogenetic development of acoustic structures in male Northern-white cheeked gibbons (Nomascus leucogenys) and Southern-yellow cheeked gibbons (Nomascus gabriellae). The results showed that the first time immature males (juvenile and adolescent) produced female acoustically structured great calls in duets with their mothers. How the great call was structured in immature males differed from the great call of their mothers; the difference being in spectro-temporal parameters from. The most significant difference between juvenile and adolescent males in the production of female vocalization was the presence of a twitter vocalization towards the end of their call. The results show that the twitter was a regular part of female vocalization in juvenile males around four years of age, while younger males produced this vocalization exceptionally. The second period in the ontogeny of vocalization in immature males (adolescent) was characterized by the fact that after five years of age, the development of the male acoustic structure begins. During this period, we did not observe the production of the female vocalization great call in any of the monitored Nomascus gibbon individuals. Results show that the ontogenetic process of the male song in Northern-white cheeked gibbons (N. leucogenys) did not develop in the same sequence as in adults which produced different notes and phrases. The immature male (adolescent male) first time developed the multi-modulation phrase (coda) and the staccato note (syllables) simultaneously at the beginning of this study, but, it was observed that they started producing the boom note four months later. Conversely, the development of the acoustic structure in male Southern-yellow cheeked gibbons (N. gabriellae) was characterized only by the development of a multi-modulation phrase. Development of the staccato syllables was not noted in this species during the study. The results support the interpretation that the development of the male acoustic structure closely corresponds to the growth of the vocal tract and physiological changes associated with reaching sexual maturity.

The endangered white-cheeked crested gibbon (Nomascus leucogenys), native to Laos, Vietnam, and perhaps China, remains little known and highly threatened. I studied seasonal variation in the diet, activity budget, and ranging behavior of three groups of white-cheeked crested gibbons in Nam Kading National Protected Area, Bolikhamxay Province, Laos, over 12 months in wet seasonal evergreen forest. Crested gibbons (Nomascus spp.) are speculated to be more folivorous than other gibbons, but this has never been confirmed because of the paucity of fieldwork on the genus. I studied diet in relation to forest seasonality to determine the contribution of leaves to the diet over an annual cycle. Although leaves were the main dietary item throughout the year (53-85% of monthly diet), gibbons substantially increased their consumption of fruit during periods when it was most abundant in the forest. Because fruit is a calorically rich source of food, gibbons seek fruit when it is abundant and obtained easily. Young leaf consumption increased when they did not have access to fruit, indicating that their diet is flexible but strongly dependent on seasonal availability of resources. In addition, rainfall had a negative association with fruit abundance and fruit in diet. Activity budgets are an important aspect of a species' ecology because they are directly related to home range use, energy allocation, and diet, but they have never before been studied in gibbons (Nomascus spp.) of the rainy, mountainous, forests of Laos. Annually, the three groups that I studied spent nearly equal amounts of time resting (30%), feeding (33%), and traveling (35%), but only a small amount of time singing (2%). However, the proportion of time allocated to different activities showed significant seasonal variation associated with rainfall and diet, and correlated with home range use. Gibbons increased traveling time and decreased feeding time when they ate more fruit, and they decreased traveling time and increased feeding time when they ate more leaves. When the gibbons spent more of their time traveling, they also had longer day range lengths, and used a higher percentage of their total home range. Moreover, when rainfall was high, the gibbons decreased traveling time and increased time resting and feeding. Average home range size was 37.9 hectares and daily average distance over which the gibbons ranged over the 12 month study was 1.48 km per day. Differences existed among the three groups. Overall, white-cheeked crested gibbons have a home range similar in size or larger than frugivorous gibbons, and larger than the folivorous siamang. Ranging was highly seasonal with shorter day ranges during times of low fruit availability and consumption. During times of high fruit availability and low rainfall, the gibbons took on an energy maximizing strategy where they maintained large home ranges, traveled longer distances and consumed larger quantities of fruit. Gibbons and their habitat in Laos have faced continuous threats over the past 10 years because of large scale development projects and subsistence hunting. Given the highly threatened status of the species in Vietnam and China, the Lao population is certainly the world's largest and the best hope for conservation of behavioral, ecological, and genetic diversity. Resources for conserving species in the country are very limited, and wildlife populations are already greatly fragmented. I describe the current conservation issues and based on the dietary and ranging information that I collected, recommend important conservation measures to safeguard the remaining populations of endangered gibbons from extinction.

Diploma thesis--Anthropological Institute and Museum, University of Zürich, 2004. / "2004"--title page. Title from initial PDF page image (viewed October 5, 2006). Includes bibliographical references (p. 59-63).

The gibbon primates of the family Nomascus are classified as critically endangered species, and, to date, basic understanding and information about their biology is missing. With regard to the status of these animals in the wild and captive populations in zoos, being familiar with their reproduction, may improve captive breeding programs. Data collection in this study was to be carried out by the practical use of non-invasive methods (polymerase chain reaction for DNA extraction and enzyme immunoassays), using faecal samples for analysis. The first method, polymerase chain reaction, was used for sex determination in juveniles, because of their coat colour and visual similarity of secondary sex characteristic in both sexes; it is not possible to determinate sex without handling the animal. Another main purpose of this study is to try and answer the hypothesis regarding the ovarian cycle of females, factors influencing their hormone concentration and also the onset of sexual maturity in females and the timing of their fur colour change. Hypotheses were checked by monitoring the concentration of progesterone and oestrogen faecal metabolites and by evaluation of the composition of breeding groups of gibbons with the ZOO influence. During a four year period (from 2010 till 2014), there were a total of 51 animals analysed from 16 different zoos with a faecal sample count totalling 1618 samples. The results confirmed the use of noninvasive methods for sex determination, and thus ensuring the maximum welfare standards. Endocrinological analysis confirmed the hypothesis of the influence of the environment (ZOO) to the hormone concentrations and female´s pregnancy effect in conjunction with her age on the final results of the male - father hormone concentrations. The initial information in this study is the confirmation of the onset of ovarian cycle in young females without connection to their fur colour change and a significant factor of a mother´s impact and her territoriality. This study is the first to present a long term monitoring of ovarian cycles in females and hormone concentrations of other individuals, both male and female, and from various age groups. The results allow us to understand the possible impact of zoo environments on the reproductive status of these gibbons and contribute to the general improvement of breeding management.

No description available.