Preliminary Study On Feeding Ecology Of Eastern Black Crested Gibbon (nomascus Nasutus) At Jingxi County In Guangxi

The eastern black crested gibbon, Nomascus nasutus, belongs to Primates order, Haplorrhini suborder, Hylobatidae family, Nomascus genus. It has only recently been recognized as a species distinct from the western black crested gibbon, Nomascus concolor and includes two subspecies (N. n. hainanus and N. n. nasutus). Because of the significant difference in coloration, sonogram structure and genetics, many gibbon experts regard them as two distinct species (N. hainanus and N. nasutus).Eastern black crested gibbon historically distributed in south China and north Vietnam, eastern of Red River. However, it was thought to extinct in China since 1950s. In Vietnam, the last reliable record for the occurrence of this subspecies stems from the 1960s. In January 2002, a small remnant population was re-discovered by FFI survey team in Trung Khanh district of Cao Bang Province, Vietnam, on the Chinese border. Because the gibbons occur very close to the Chinese border, Kadoorie Farm & Botanic Garden and Jingxi Forestry Bureau did a survey in China in September 2006 and sighted three groups with 19 individuals. To obtain the accurate information of population size of this species, a survey team consisted of Chinese and Vietnamese experts and ranges did an extensive survey cover the whole habitat of this species in september 2007, and discovered 18 groups, about 100 individuals. This is the last population of this species. And now eastern black crested gibbon was categoried as Critically Endangered in IUCN Redlist, and was listed as one of the World's 25 Most Endangered Primates 2008– 2010 during the XXII Congress of the International Primatological Society.Karst forest, eastern black crested gibbon's habitat, is different from the typical gibbon's habitat. Studying gibbons in karst forest not only add knowledge to the gibbons'adaptation strategies, and also contribute to conservation of this critically endangered species. The feeding behaviour of a group of eastern black crested gibbon was studied in Bangliang (22°55′N, 106°29′-30′E), Jingxi County, Guangxi Province, China from December 2007 to February 2009. An automatic data recorder (Hobo pro, RG3-M) was set in the nearest village, 3 Kmaway from the study site. It can automaticlly recorde the temperature every half an hour and recorde the rainfall continuously. The annual mean temperature was 30.3℃between January and December 2008. The lowest mean temperature was February (9.8℃), and the highest was September (26.6℃). The minimum recorded temperature was 2.7℃in February, and the maximum was 40.7℃in September. Precipitation was 1,803.8 mm during January and December 2008. We measured 911 tree individuals with DBH≥10 cm in the 44 plots, of them 838 individuals were identified to species. We recorded 114 species of tree from 79 Genera and 40 Families; 51 species of woodiness liana from 38 Genera and 26 Families. On average, the tree height is only 9 m, the highest tree is 32 m, which is much lower than those in other gibbon's habitat. The mean value of DBH was 17.4 cm and mean diameter of crown was 5 m.Avalability of buds and fruit showed significant seasonal variation (χ~2 = 23.677, P = 0.000), while no significant variation was found in the availability of leaves and figs. Buds were available between January and June. More fruit was available from September to November.Quantitative observations of behavior were made by scan sampling at 5-min intervals. Gibbons consumed 57 different plant species and several unidentified plant and animal species. Eleven important plant species and animals accounted for 75.5% of the total diet. Gibbons spent 33.3% of their time feeding in fruit between March 2008 and February 2009. In descending order, the remainder of the diet was made up figs (26.3%), leaves (23.0%), buds (6.5%), animals (9.8%), flowers and lichen (1.1%). There was a significant difference in the proportion of different foods types eaten in different time (χ~2 =70.20, P = 0.000). Over the course of a day, fruits tended to be eaten early in the morning and in the later afternoon. Gibbons have to eat fruit to increase a low level of blood sugar as a result of the overnight fast, and they stock up on an energy-rich food to get them through the night. There was marked seasonal variation in dietary proportions (χ~2 = 47.111, P = 0.000). When fruit was not abundant, gibbons increased time feeding in leaves. But they preferred fruit when it was abundant. Fruit accounted for 92.9% of the monthly diet in November 2008. Figs were important fallback food resources for gibbons in the study site. Several fig species provided fruit for gibbons in different month and productivity of figs showed no seasonal variation during the study period. Gibbons spent more time feeding in animals between June and October when animals were more abundant.Annually, the study group spent an average of 40.1% of the time resting, 23.7% feeding, 19.6% traveling, 9.9% grooming, and 2.9% in other activities. Gibbons showed significant diurnal variation in their time budget (χ~2 = 61.091, P = 0.000). During the day, feeding manifested a bimodal pattern of high activity levels in 0800 and 1600, whereas resting reached a peak at midday. The proportion of time allocated to activities showed significant monthly variations (χ~2 = 47.111, P = 0.000) and was influenced by the diet and temperature. Gibbons increased social behavior (grooming and playing) and decreased feeding time and resting time when they fed mainly on fruit. Gibbons increased resting and feeding time and decreased social behavior when they spent more time feeding in leaves in the cold season.Behavioral data from this site are particularly useful in understanding gibbon behavioral adaptations to different sets of ecological conditions. This is the first study focused on the gibbon's feeding behavior in karst forest. The feeding behavior of eastern black crested gibbon was influenced by the temperature and plant phenology. Summary, eastern black crested gibbon employed high-effort activities when they ate more fruit and energy-conservation patterns when they ate more leaves and in low temperature.