The ecology of singing in Kloss gibbons (Hylobates klossii) on Siberut Island,Indonesia

Data are presented from a study of habituated Kloss gibbons on Siberut Island, Indonesia. Male Kloss gibbons can sing at any time from 0100 to 1300 hr, but the majority of songs is concentrated in the hour before dawn. Female Kloss gibbons sing only after dawn and the song bout includes a dramatic visual display. Neither countersinging nor coordinated chorusing has been proved in either sex. Males sing before dawn as often as possible but are inhibited by wet nights and by minimum temperatures below 21.5°C; postdawn songs of both sexes are inhibited by rain. The occurrence of any particular type of song bout is independent of the occurrence of the other types. Song trees used by males and those used by females do not differ in height. Song trees emerged from the neighboring canopy more than other available trees of similar height in the gibbons’ home range. Female song trees were most abundant on the slopes and where the trees were tallest. Almost all the male’s night trees could have been used for singing from had the weather been suitable. There was a greater likelihood of the male’s traveling a long way to the day’s first fruit source on mornings when he sang before dawn than on mornings when he did not. Considerations of sound transmission through tropical rain forest reveal that the times and frequencies used for singing by Kloss gibbons are optimal for communicating with neighboring groups.     

Singing by male and female Kloss gibbons (Hylobates klossii) in the Peleonan Forest, Siberut Island, Indonesia

Kloss gibbons (Hylobates klossii) are endemic to the Mentawai Islands in Indonesia and are one of only two gibbon species in which mated pairs do not sing duets. This is the first long-term study of the factors influencing the singing activity of Kloss gibbons within a northern Siberut Island population and follows two previous studies in central Siberut nearly 30 years ago. We collected data on the presence/absence of male and female singing within the study area on 198 days and within a focal group on 47 days. Rainfall during the time period in which they normally sing inhibits singing in both males and females. Our study supports the hypothesis that male and female songs function in intrasexual resource defence, as singing is associated with singing by same-sex neighbours, and same-sex choruses are more likely to occur after one or more days of silence (from that sex), suggesting there is pressure for individuals to communicate with same-sex neighbours regularly. Singing was not coordinated within a mated pair, suggesting that vocal coordination of the pair has been lost with the loss of the duet and that Kloss gibbon songs do not convey information to neighbours about the strength of the pair bond. On days when males sang predawn, females were more likely to sing after dawn and earlier in the morning. Additionally, the number of groups singing in female choruses was positively associated with the number of males that had sung in the predawn male chorus. We suggest that female songs have an intersexual territory defence as well as an intrasexual function.     

Inter‐group variability in seed dispersal by white‐handed gibbons in mosaic forest

Seed dispersers, like white‐handed gibbons (Hylobates lar), can display wide inter‐group variability in response to distribution and abundance of resources in their habitat. In different home ranges, they can modify their movement patterns along with the shape and scale of seed shadow produced. However, the effect of inter‐group variability on the destination of dispersed seeds is still poorly explained. In this study, we evaluate how seed dispersal patterns of this arboreal territorial frugivore varies between two neighboring groups, one inhabiting high quality evergreen forest and one inhabiting low quality mosaic forest. We predicted a difference in seed dispersal distance between the two groups (longer in the poor quality forest). We hypothesized that this difference would be explained by differences in home range size, daily path length, and ranging tortuosity. After 6 months of data collection, the evergreen group had a smaller home range (12.4 ha) than the mosaic group (20.9 ha), significantly longer daily path lengths (1507 m vs. 1114 m respectively) and greater tortuosity (39.1 vs. 16.1 respectively). Using gut passage times and displacement rates, we estimated the median seed dispersal distance as 163 m for the evergreen group (high quality forest) and of 116 m for the mosaic group (low quality forest). This contradiction with our initial prediction can be explained in term of social context, resource distribution, and habitat quality. Our results indicate that gibbons are dispersers of seeds between habitats and that dispersal distances provided by gibbons are influenced by a range of factors, including habitat and social context.     

Ranging behavior of eastern hoolock gibbon (Hoolock leuconedys) in a northern montane forest in Gaoligongshan,Yunnan, China

Generally, food abundance and distribution exert important influence on primate ranging behavior. Hoolock gibbons (genus Hoolock) live in lowland and montane forests in India, Bangladesh, Myanmar and China. All information about hoolock gibbons comes from studies on western hoolock gibbons (Hoolock hoolock) living in lowland forest. Between August 2010 and September 2011, we studied the ranging behavior of one habituated group of eastern hoolock gibbon (H. leuconedys) living in a seasonal montane forest in Gaoligongshan, Yunnan, China. Results show that the study group did not increase foraging effort, calculated in this study as the daily path length, when fruit was less available. Instead, the gibbons fed more on leaves and decreased traveling to conserve energy. They relied heavily on a single food species in most study months which was patchily distributed within their total (14-month) home range, and during most months they used only a small portion of their total home range. In order to find enough food, the group shifted its monthly home range according to the seasonal availability of food species. To satisfy their annual food requirements, they occupied a total home range of 93 ha. The absence of neighboring groups of gibbons and the presence of tsaoko cardamom (Amomum tsaoko) plantations may also have influenced the ranging behavior of the group. Further long-term studies of neighboring groups living in intact forests are required to assess these effects.     

西黑冠长臂猿隔离小种群栖息地植被特征与其食性及生境利用

由于长期的捕猎及森林破坏,许多西黑冠长臂猿群体生活于零散的小型生境片段中。在云南南部芭蕉河地区,利用55个样方测量了西黑冠长臂猿一个隔离小种群栖息地植被,共记录乔木28科57属85种,其中壳斗科、樟科及省沽油科占优势地位,植被组成与结构在不同的森林片段、地形及干扰程度区域中差异显著。利用瞬时扫描法在两个年周期中的系统观察发现,与连续森林中的群体相比,芭蕉河长臂猿更加依赖对桂北木姜子、大果山香圆等优势乔木树种的取食,在乔木果实缺乏的季节,其并未取食更多叶类,而是进入次生植被搜寻藤本果实。可能受人为干扰及植被结构的影响,长臂猿未取食无花果类植物。原始林中植被结构并未对长臂猿生境利用造成明显影响,但其在不同森林片段间表现出显著的选择性。通过对芭蕉河、大寨子、平河及新平茶马古道四地的比较发现,西黑冠长臂猿栖息地植被特征存在较大的地区差异,其生态与行为可能因此表现出较强的适应性,但这需要更大时空尺度的研究予以验证。     

Coexistence of monogamy and polygyny in black-crested gibbon (Hylobates concolor)

All gibbons are monogamous and territorial with the exception ofHylobates concolor. This paper reports the coexistence of monogamy and polygyny in black-crested gibbons. Based on the fact of two adult females and two offspring of the same age category in one group and other reasons, we suppose that the two adult females have bred in a single group, i.e. a polygynous one. The other main reasons are: (1) a large home range makes it possible for more individuals to live in one group; (2) mutual tolerance among two females; and (3) selection pressure favouring polygyny.     

黑长臂猿（Hylobates concolor）的配偶制及其与行为、生态和进化的关系

黑长臂猿是猿类中野外行为生态研究最少的一种,因而对其社群结构及配偶体制一直有着很大争议．本文基于近两年在无量山和哀牢山１０个月的野外工作,着重阐述了黑长臂猿的配偶体制,我们认为黑长臂猿是以一夫一妻和一夫多妻（至少是一夫两妻）的形式存在,并与其行为、生态及系统发育相关联．黑长臂猿的系统发育地位、成年雌性的领域性及群体的领域性不强和群体的领域较其它长臂猿类大得多可能是形成一夫多委的原因;而黑长臂猿在中国各分。布区的生境均受到不同程度的破坏,这在一定程度上也影响着其社群结构,特别是狩猎有着更直接的影响,活动范围的限制等,可能是形成一夫一妻的原因．     

Effects of food and topography on ranging behavior of black crested gibbon (Nomascus concolor jingdongensis) in Wuliang Mountain, Yunnan, China

We studied the ranging behavior of a habituated group of black crested gibbons (Nomascus concolor jingdongensis) in a high, seasonal habitat on Mt. Wuliang, central Yunnan, China, between March 2005 and April 2006. Our results indicated that the total home range size for the study group was 129 ha, or 151 ha if the lacunae within the borders in which gibbons were not observed were included. This is a much bigger range size than that of other gibbon species. However, 69.7% of their activities occurred within 29 ha. The intensity of quadrant use was significantly correlated with the distribution of important food patches. The mean yearly daily path length was 1,391 m. Gibbons traveled farther when they spent more time feeding on fruit. To avoid often passing through ridges with little food, gibbons usually stayed in the same valley for successive days, and then moved on to another valley for another several days, which resulted in a concentrated ranging pattern.     

白眉长臂猿鸣叫的时间特征

滇西白眉长臂猿(Hylobateshoolock)鸣叫主要发生在上午,最早开始于黎明时分,最晚则在下午16:30以后。平均开始时间为09:05,SD=1095min(N=70,范围07:12～16:30),持续时间为197min,SD=934min(N=55,R=4～50)。多数鸣叫发生在07:00～10:00之间(80%)。不同季节鸣叫发生时间有显著差异,可能与黎明时间(光亮度)不同有关,但持续时间无差异。同一季节异地间鸣叫持续时间差异显著。气候、猿群密度、栖息地状态对鸣叫有一定影响,但未见明显相关性。与黑长臂猿的种间比较表明,白眉长臂猿的鸣叫声在时间分布上有较大的散开度,持续时间也较长,二者有显著差异。     

How Reliable are Density Estimates for Diurnal Primates?

Primate population assessments provide the basis for comparative studies and are necessary prerequisites in determining conservation status. The most widely used assessment method is line transect sampling, which generates systematic data quickly and comparatively inexpensively. In contrast, the presumably most reliable method is long-term monitoring of known groups, which is both slow and costly. To assess the reliability of various analytical methods, we compared group and population densities for white-handed gibbons (Hylobates lar carpenteri) and Phayre’s leaf monkeys (Trachypithecus phayrei crepusculus) derived from transect walks with those from long-term group follows at Phu Khieo Wildlife Sanctuary, Thailand. Our assistants and we regularly walked a 4-km transect over 30 mo (480 km total), resulting in 155 gibbon sightings and 125 leaf monkey sightings. We then estimated densities via 1) DISTANCE and 2) the Kelker method based on perpendicular distances (PD) or animal-to-observer distances (AOD). We compared the 3 estimates to values based on known home ranges (95% kernels), accounting for home range overlap, combined with group size data. Analyses of line transect data consistently overestimated group densities for both species, while underestimating group size for leaf monkeys. Quality of results varied according to the group size and spread of each species. However, we found, in accordance with previous studies, that values derived via AOD (or its derivations) matched most closely with population estimates based on home range data.     

Siamangs (Hylobates syndactylus) and White-Cheeked Gibbons (Hylobates leucogenys) Show Few Behavioral Differences Related to Zoo Attendance

The effect of visitors on behavior and welfare of nonhuman animals in the zoo has been an active research topic during the last few decades. Although research has variously shown negative or positive impacts of zoo visitors on animals in captivity, previous primate research at Disney's Animal Kingdom® suggests the importance of visual barriers in allowing animals to cope with large crowds. Examining this further, this study monitored the behavior of white-cheeked gibbons (Hylobates leucogenys) and siamangs (Hylobates syndactylus) in large, open exhibits. Behavioral data showed rates of social behavior and percentage of time engaged in solitary behavior did not differ between low and high visitor-attendance days. Both gibbons and siamangs spent more time in areas away from the public on high attendance days. Supporting previous findings, results imply visual barriers and ability to retreat from crowds may have provided these animals with choice and minimized potential negative visitor impact. Future research should focus on the relationship between attendance and actual crowds at exhibits; it should utilize multi-institutional methodologies to control for variance and look for individual and demographic differences between individuals.     

Location-specific Responses of Gibbons (Hylobates muelleri) to Male Songs

I investigated the responses of gibbons (Hylobates muelleri) to male songs played back from different locations but similar distances from the subjects. The gibbons showed spatial variations in response to songs. Mated males led silent group approaches toward songs emanating from the center of the range. Songs delivered from positions along the range periphery elicited either group approaches or duets. Songs played back from within the ranges of neighbors rarely resulted in duetting activity. Location, a contextual factor, is important in determination of the response evoked by song. These results are consistent with the hypothesis that male song plays a role in mediating intergroup spacing among gibbons.     

Non‐territorial Macaques Can Range Like Territorial Gibbons When Partially Provisioned With Food

Human food supplementation can affect components of animal socioecology by altering the abundance and distribution of available food. We studied the effect of food supplementation by comparing the ranging patterns and intergroup interactions of two groups of northern pigtailed macaques (Macaca leonina), a non‐territorial primate species. One group was partially reliant on food provisioning, whereas the other group foraged wild food. We also compared the macaques’ movement with that of a group of white‐handed gibbons (Hylobates lar), a territorial species inhabiting the same site. Home range, core area, and daily path lengths were significantly smaller for the semi‐provisioned group than for the wild‐feeding group. In contrast to wild‐feeding macaques, supplemented macaques showed higher fidelity to home range, core area, and particularly to the region where human food was most accessible and abundant. The relationship of daily path length and home range indicated a low defendability index for wild‐feeding macaques; the higher index for the semi‐provisioned group was consistent with the territorial pattern found in gibbons. Semi‐provisioned macaques showed further traits of territoriality with aggression during intergroup encounters. These findings indicate that human modification of food availability can significantly affect movement patterns and intergroup competition in macaques. The observed ranging dynamics related to food provisioning may decrease the efficiency of macaques as seed dispersers and increase predation on their home range, and thus have important consequences for plant regeneration and animal diversity.     

景东无量山自然保护区黑长臂猿的数量与保护

无量山地处云南中部,为黑长臂猿（Ｈｙｌｏｂａｔｅｓｃｏｎｃｏｌｏｒ）的主要分布区之一。近年来国内外学者虽然对黑长臂猿进行了较多的行为,生态与保护研究,然而有关该地区黑长臂猿的数量估计却有很大差异（６６－３００群）如：蓝道英（１９８９）报道有６６－１４４群,Ｈａｉｍｏｆｆ等（１９８６）认为有２２５－２５０群,Ｂｌｅｉｓｃｈ等（１９９）也认为有较多的群体,达１６０－３００群之多,而Ｚｈａｎｇ等（１９９     

Gibbons (Nomascus gabriellae) provide key seed dispersal for the Pacific walnut (Dracontomelon dao), in Asia's lowland tropical forest

Understanding the mutualisms between frugivores and plants is essential for developing successful forest management and conservation strategies, especially in tropical rainforests where the majority of plants are dispersed by animals. Gibbons are among the most effective seed dispersers in South East Asia's tropical forests, but are also one of the highly threatened arboreal mammals in the region. Here we studied the seed dispersal of the Pacific walnut (Dracontomelon dao), a canopy tree which produces fruit that are common in the diet of the endangered southern yellow-cheeked crested gibbon (Nomascus gabriellae). We found that gibbons were the most effective disperser for this species; they consumed approximately 45% of the fruit crop, which was four times more than that consumed by macaques – the only other legitimate disperser. Gibbons tracked the temporal (but not spatial) abundance of ripe fruits, indicating this fruit was a preferred species for the gibbon. Both gibbons and macaques dispersed the majority (>90%) of the seeds at least 20 m away from parent crowns, with mean dispersal distances by gibbons measuring 179.3 ± 98.0 m (range: 4–425 m). Seeds defecated by gibbons germinated quicker and at greater rates than seeds spat by macaques, or in undispersed fruits. Gibbon-dispersed seeds were also more likely to be removed by unknown seed predators or unknown secondary dispersers. Overall, gibbons play a key role in the regeneration of the Pacific walnut. Our findings have significant implications both for the management of the Pacific walnut tree dominating tropical rainforest as well as the reintroduction program of the Southern yellow-cheeked crested gibbon.     

Speed modulation in hylobatid bipedalism: a kinematic analysis

Gibbons are highly arboreal apes, and it is expected that their bipedal locomotion will show some particularities related to the arboreal environment. Previous research has shown that, during hylobatid bipedalism, unsupported phases are rare and stride frequencies are relatively low. This study confirms previous findings, and we suggest that low stride frequencies and the absence of unsupported phases are ways to reduce disadvantageous branch oscillations during arboreal travel. Despite these restrictions, gibbons are able to locomote at a wide range of speeds, implying that they likely exploit other mechanisms to modulate their locomotor speed. To investigate this possibility, we collected video images of a large number of spontaneous bipedal bouts of four untrained white-handed gibbons by using an instrumented walkway with four synchronized cameras. These video images were digitized to obtain a quantification of the 3D kinematics of hylobatid bipedalism. We defined a large number of spatiotemporal and kinematic gait variables, and the relationship between these gait variables and (dimensionless) speed was statistically tested. It was found that gibbons mainly increase stride length to increase their locomotor speed; the main speed-modulating mechanisms are hip and ankle excursion and coupled knee and ankle extension at toe-off. Although aerial phases are rare, gibbons generally adopt a bipedal bouncing gait at most speeds and a clear-cut gait transition, as seen in human locomotion, is absent. Comparison with human and bonobo bipedalism showed that the variability of the 3D joint angles of the hind limb are comparable during human and gibbon bipedalism, and much lower than during bonobo bipedalism. The low variability found in gibbons might be related to constraints imposed by the arboreal environment. These arboreal constraints clearly affect the bipedal gait characteristics of gibbons, but do not constrain the ability to adopt a bipedal bouncing gait during terrestrial locomotion.     

Conservation Value of Landscape Supplementation for Howler Monkeys Living in Forest Patches

Many animal populations are forced to inhabit very small forest patches, which may threaten their long-term survival. In some cases, animals in these forest remnants are able to supplement their diet by using resources outside of their home patch, a process named 'landscape supplementation'. Although this is probably a key process for population survival in fragmented landscapes, little is known about the ability of most animal species to move through the matrix and feed from different landscape elements. In this paper we report several cases of landscape supplementation by two groups of Mexican mantled howler monkeys Alouatta palliata mexicana inhabiting two different forest patches in Los Tuxtlas, Mexico. Our observations show that howler monkeys used several landscape elements, such as isolated trees, live fences and neighboring forest patches to supplement their diet. These observations underline the importance of these landscape elements for the survival of forest-dependent animals in highly fragmented landscapes, as they can provide important food resources and, hence, can be considered as potential extensions of their home range. However, the degree of protection the landowner provides to howler monkeys and proper management of these landscape elements are key aspects in determining the use of these elements by these animals.     

The effect of supplementary food on home range of the southern brown bandicoot,Isoodon obesulus (Marsupialia: Peramelidae)

The study investigated the relationship between home range and food abundance in a population of the southern brown bandicoot. Isoodon obesulus, in Western Australia. Home range areas were estimated seven times between 1986 and 1988 by live-trapping, spool-and-line devices and fluorescent pigment tracking. The abundance of invertebrate food was measured simultaneously by placing pitfall traps within the home ranges of individual animals, and by sampling invertebrates in topsoil and litter. Home range areas tended to be negatively correlated with food abundance, especially in the autumn and winter of 1986 and 1987. The influence of food on home range was investigated further in September 1988 by providing eight individual I. obesulus with a supplementary food mixture. Contrary to expectation, the added food caused an increase in home range area, home range overlap and displacement, as well as an influx of new individuals to food stations. In contrast, home range parameters in control (non-fed) individuals changed little during the experiment. The shuffling of home ranges due to feeding suggests that the home range system of I. obesulus is relatively flexible, with individuals monitoring and exploiting resources in an opportunistic manner. In contrast to previous studies, we found no evidence that I. obesulus was territorial. We speculate that individuals may be territorial at low population density if resources are defendable and intruder pressure is low, but occupy overlapping ranges if population density is high.