Primates

, Volume 52, Issue 1, pp 51–60

Sleeping site selection of Francois’s langur (Trachypithecus francoisi) in two habitats in Mayanghe National Nature Reserve, Guizhou, China

Authors

  • Shuangling Wang
    • Guangxi Forest Inventory and Planning Institute
    • College of Nature ConservationBeijing Forestry University
  • Yang Luo
    • China Programme, Fauna and Flora International
    • College of Nature ConservationBeijing Forestry University
Original Article

DOI: 10.1007/s10329-010-0218-2

Cite this article as:
Wang, S., Luo, Y. & Cui, G. Primates (2011) 52: 51. doi:10.1007/s10329-010-0218-2

Abstract

Sleeping site selection is an important aspect of the behavioral biology of primates. Comparison of different habitats for the same species in this context enhances understanding of their adaptation to altered environments. We collected data on sleep-related behaviors for 6 groups of Francois’s langur (Trachypithecus francoisi) in two habitats, in Mayanghe National Nature Reserve, Guizhou, China. Regardless of habitat, all sleeping sites were located in areas of steep terrain of ≥60°. In undisturbed habitat, sleeping sites were located only in evergreen broadleaf forest with rock caves and crevices surrounded mainly by a vegetation layer of shrub + rock. In disturbed habitat, sleeping sites were also located in mixed evergreen and deciduous broadleaf forest and in grassland, including rock caves, crevices, and pits, surrounded mainly by arbor + shrub and shrub + rock. Wild food availability was higher in undisturbed habitat than disturbed habitat, but food abundance around sleeping sites was lower. Water sources included river and seasonal gully or pond. There was strong positive correlation between use of sleeping sites away from the river valley and occurrence of seasonal water sources. The number of sleeping sites varied across groups, numbering 6, 7, and 10 for three specific groups. Few sleeping sites were used all year round. Six consecutive nights was the longest recorded run. Francois’s langurs’ sleeping habits differed between two habitats. In undisturbed habitat, minimizing predation risk appeared to predominate, expressed by choosing steep terrain, open visual field, and inconspicuous presleeping behavior. In disturbed habitat, along with predation avoidance, food resources may strongly influence sleeping site selection, as demonstrated by the richer food abundance and greater foraging activity around the site. Finally, water resources may influence choice of sites distant from the river; such sites were used less frequently during water shortages.

Keywords

Francois’s langurTrachypithecus francoisiSleeping siteUndisturbed habitatDisturbed habitatMayanghe National Nature Reserve

Introduction

Sleeping site selection is an important aspect of the behavioral ecology of primates; it influences level of exposure to predation and movement patterns within the home range (Altmann 1974a, b; Hamilton 1982), and impacts upon fitness (Di Bitetti et al. 2000). Many factors have been suggested to explain sleeping site selection by primates, including avoiding predation (Reichard 1998; Radespiel et al. 2003; Liu and Zhao 2004), remaining close to food and water resources (Chapman 1989), sheltering from bad weather (Anderson 1998), social contact (Kinzey and Wright 1982), group contact (Chapman 1989), parasite avoidance, and range or resource defense (Heymann 1995). The types of sleeping sites used by primates are also diverse. Some are branches or other natural structures, some are nests constructed by primates, and others are tree holes or other cavities (Kappeler 1998). Use of cliff faces or caves by nonhuman primates is relatively rare, only known in baboons (Hamilton 1982; Barrett et al. 2004) and those members of the arboreal genus Trachypithecus found in forest on karst limestone hills in Vietnam and southern China (Huang et al. 2003; Cyril and Ding 2006).

Trachypithecus francoisi (Colobinae, Cercopithecidae, Primate, Francois’s langur) is found only in mountainous limestone forests in northern Vietnam and in Guangxi Autonomous Region, Guizhou Province, and Chongqing Municipality in southern China. The global population is estimated to be about 1,647–1,902 individuals (Luo 2007). Due to high levels of forest loss, the population has declined significantly (Li et al. 2007) and furthermore has been fragmented into many small subpopulations. In China, it is a first-class protected species under national wildlife law. Very little information exists on sleeping site selection in this species. Cyril and Ding (2006) reported an observation of this species using caves at Mayanghe National Nature Reserve (MYH NR), Guizhou, China. They observed 2 groups and recorded use of 2 types of caves: on cliff faces, and at the base of hills; however, no detailed information about habitat characteristics or cave use was given. At the same nature reserve, Luo et al. (2000, 2005, 2007) studied diet composition and daily activity profiles. They reported that some crops were raided by the monkeys, e.g., maize (Zea mays). Also, there were significant differences in daily activity patterns between groups in undisturbed and disturbed habitats, probably due to decreased food availability caused by human activities. We studied the home ranges of 3 groups of the langurs at the same reserve and also found marked differences in ranging patterns between these two habitats (Wang 2008).

Given the differences in activity patterns across habitats, we assessed potential differences in sleeping site selection by Francois’s langur in these two habitats. Such comparisons among populations of the same species are important for understanding the diversity of primates’ adaptations to their environment (Anderson 1998; Strier 2006). Here, we tested two hypotheses regarding influences on sleeping site selection: (1) predation hypothesis: primates select sleeping places with reduced accessibility for predators and to facilitate detection of an approaching predator; and (2) food or water access hypothesis: primates sleep near foraging sites or water sources.

Methods

The research site was situated in MYH NR in Guizhou Province, China (31,113 ha, 280–1,441 m a.s.l. 28°37′30″–28°54′20″N, 108°3′58″–108°19′45″E). The NR climate is humid subtropical with average annual temperature of 18.3°C, annual precipitation of 1,138 mm, and a long frostless season of 271 days (Chen et al. 2001). The NR consists of karst hills and includes nine vegetation types: evergreen broadleaf forest, mixed evergreen and deciduous broadleaf forest, deciduous broadleaf forest, deciduous broadleaf and coniferous mixed forest, coniferous forest, bamboo forest, shrub, grassland, and farmland, with forest cover being 63.7% (Chen et al. 2001). Mayanghe River and Hongduhe River flow through the NR. River valley vegetation is mainly evergreen forest, composed of evergreen broadleaf forest and mixed evergreen and deciduous broadleaf forest, and provides the langurs with rich food resources and natural refuges (Li 1994). Francois’s langur and Macaca mulatta are the only two nonhuman primates living at the NR. The NR has 78 groups of the langurs, about 650 individuals, mostly distributed along the river valley (Luo 2007). Generally, the groups are polygynous, with one adult male, several adult females, and their immature offsprings, with group sizes of 7–13 individuals (Li 1994). A small population of Macaca mulatta inhabits the north part of the NR.

The research site included four observation sites in the NR. Only Francois’s langurs were found at these sites. YTG, WJ, and LYY sites (320, 210, and 170 ha, respectively) were virtually undisturbed habitats where the river valley vegetation was mainly evergreen broadleaf forest, and vegetation on slopes (~45°) consisted of about 50% natural forest and 50% farmland. No road or village existed in the langurs’ home range at these three sites, and human activities including grazing, firewood collection, and farming occurred around the home range. XGB site (230 ha) was disturbed habitat: the river valley vegetation was mainly shrub forest and a few high trees, with no natural forest along the slopes. One road and 7 households were located in the home range of the monkeys, and grazing, firewood collection, farming, and a market all occurred in the home range.

We selected 2 groups in YTG, 1 group in WJ, 1 group in LYY (called lyy group), and 2 groups in XGB (called xgba group and xgbb group, respectively) for observation between October 2006 and September 2007. We followed lyy group, xgba group, and xgbb group each season, YTG groups in only summer, and WJ group in spring. We recorded the location of the groups on a 1:10,000 scale map at 15-min intervals and used the ad libitum method (Altmann 1974a, b) to record the langurs’ times of entering sleeping sites, any presleeping behaviors, and intergroup encounters when possible. A total of 23 sleeping sites were located and marked on the map. For each sleeping site, we recorded 12 habitat factors (see Table 1 for descriptions and survey methods). For vegetation type, slope gradient, slope direction, slope position, and elevation, the percentage of a particular category within the home range of the monkeys was considered as availability area. To test for selection or avoidance of a particular category, Ivlev’s electivity index Ei was calculated as Ei = (ui − ai)/(ui + ai), where ui is the mean proportion of observations in a particular category and ai is the mean proportion of this category available in the home range (Lechowicz 1982).
Table 1

Frequency distribution and electivity index of habitat factors in sleeping site selection of Francois’s langur in different habitats in MYH NR

Habitat factor

Description

Category

FD

lyy group

xgba group

xgbb group

UH

DH

Ei

O

Ei

O

Ei

O

Location

 

On the river valley cliff

100

54

 

100

 

71

 

50

On the other cliff

0

46

 

0

 

29

 

50

Vegetation type

Nine categories mentioned in the description of the NRb

Evergreen broadleaf forest

100

46

0.35

100

0.75

71

0.56

50

Evergreen mixed forestf

0

38

 

0

 

0

0.37

50

Grassland

0

16

 

0

−0.05

29

 

0

Type of sleeping site

According to appearance, proportion of length to width, and direction of exposure of the entrancec

Rock cave

30

23

 

17

 

14

 

20

Crevice

70

46

 

83

 

57

 

60

Rock pit

0

31

 

0

 

29

 

20

Vegetation layer

Predominant type appearing in a 10 m radius centered on the sleeping sited

Arbor

10

0

 

17

 

0

 

0

Arbor + shrub

0

46

 

0

 

43

 

50

Arbor + shrub + rock

0

8

 

0

 

14

 

10

Shrub

10

8

 

17

 

14

 

0

Shrub + rock

80

38

 

66

 

29

 

40

Slope gradient

Clinometer data for reachable sleeping sites and ArcView3.2 data for unreachable ones

≤30°

0

0

 

0

 

0

 

0

30°–60°

0

0

 

0

 

0

 

0

≥60°

100

100

0.32

100

0.67

100

0.70

100

Slope direction

Compass data for reachable sleeping sites and ArcView3.2 data for unreachable ones

East

0

0

 

0

 

0

 

0

West

10

23

 

0

−0.03

29

−0.04

20

South

20

8

−0.03

33

0.27

14

−0.02

10

North

40

16

0.05

33

 

0

0.29

20

Southeast

0

16

 

0

 

0

0.25

20

Northeast

0

23

 

0

0.66

29

0.36

30

Southwest

20

8

0.61

33g

0.38

14

 

0

Northwest

10

8g

 

0

0.56

14

 

0

Slope position

 

Higher

30

31

 

0

−0.21

29

−0.41

20

Middle

10

31

−0.25

17

 

0

0.27

40

Lower

60

38

0.47

83

0.43

71

0.16

40

Elevationc

GPS data for reachable sleeping sites and ArcView3.2 data for unreachable ones

400–500 m

60

23

0.50

83

0.37

43

−0.20

20

500–600 m

10

46

−0.31

17

−0.21

29

0.01

60

600–700 m

0

31

 

0

−0.11

29f

0.29

20

>700 m

30

0

 

0

 

0

 

0

Food abundance

All food trees within a 10 m radius centered on the sleeping sitee

<5

60

31

 

67

 

43

 

20

5–10

40

54

 

33

 

57

 

60

>10

0

15

 

0

 

0

 

20

Distance from sleeping site to the nearest water source

Including river and seasonal water source

<50 m

0

38

 

0

 

45

 

40

50–100 m

50

23

 

83

 

14

 

20

100–200 m

20

31

 

17

 

29

 

40

200–300 m

20

8

 

0

 

14g

 

0

>300 m

10

0

 

0

 

0

 

0

Vertical distance to the top of the cliffa

By spatial analysis in ArcView3.2

<10 m

0

23

 

0

 

43

 

10

10–100 m

80

77

 

100

 

57

 

90

>100 m

20

0

 

0

 

0

 

0

Vertical distance to the bottom of the cliffa

By spatial analysis in ArcView3.2

<10 m

0

8

 

0

 

0

 

10

10–100 m

50

92

 

67

 

100

 

90

>100 m

50

0

 

33

 

0

 

0

FD frequency distribution (%), UH undisturbed habitat, DH disturbed habitat, Ei selection index, O observed frequency (%)

aThis factor would be measured if the slope gradient of a sleeping site was ≥60°

bVegetation type included evergreen broadleaf forest, mixed evergreen and deciduous broadleaf forest, deciduous broadleaf forest, deciduous broadleaf and coniferous mixed forest, coniferous forest, bamboo forest, shrub, grassland, and farmland; only those where sleeping sites were distributed, as listed and analyzed in the next column, are shown

cThis factor was divided into three categories: rock cave, being ≤3 times longer than wide, with the entrance not exposed to the sky; crevice, being >3 times longer than wide, with the entrance not exposed to the sky; and rock pit, having an entrance exposed to the sky, regardless of length-to-width ratio

dFrancois’s langurs usually gathered in this area of a 10 m radius centered on the sleeping site about 30 min after leaving the sleeping site at dawn and before they entered at dusk (Wang 2008)

eFrancois’s langurs usually fed in such areas (Li 1994; Luo et al. 2005, 2007; Wang 2008) when they left their sleeping site at dawn and approached it at dusk

fThis category means evergreen broadleaf and deciduous broadleaf mixed forest

gValues differing from 100% are due to round-off errors

In addition to food abundance around sleeping sites, we measured wild food availability in the home range using the point-center-quarter method (Cottam and Curtis 1956). We used every reachable path as a transect and established points every 10 m. We analyzed leaf and flower availability at the basal area of food trees, assuming that this area correlated with leaf and flower availability (Fujimori 2001). We estimated annual wild fruit production by noting the number of fleshy fruits on marked branches of each tree. When this was impossible, we estimated the total fruits of an individual tree by the percentage in volume of the branch to the total crown (Haya et al. 2005). Crop fruit availability was estimated on the basis of the plantation area of crops in the home range. Any water sources used for drinking were marked on the map.

We compared food availability between two habitats using the chi-square test. We classified two categories of location of sleeping site: on the river valley cliff or not, and also classified occurrence of seasonal water sources into yes or no, i.e., if there was seasonal water source near one sleeping site, we recorded it as “yes”; if there was no seasonal water source near a site, it was recorded as “no”. Then we used Spearman’s rank correlation coefficient to examine whether there was correlation between location of sleeping site and occurrence of seasonal water sources. We used one-way analysis of variance (ANOVA) to test seasonality effects on usage of sleeping site. All data were analyzed using SPSS 13.0 software.

Results

Frequency distribution of habitat factors

Table 1 presents the frequency distribution of different habitat factors. Only for slope gradient did Francois’s langur select the same category in both habitats, i.e., all sleeping sites were on steep terrain of ≥60°. For other habitat factors, generally, categories were selected more diversely in disturbed habitat than undisturbed habitat. In undisturbed habitat, sleeping sites were all located on the river valley cliff and in evergreen broadleaf forest with slope direction mainly towards the north. Usually, caves or crevices surrounded mainly by vegetation layer of shrub + rock were used, mostly on a lower slope. In disturbed habitat, sleeping sites were located not only on the river valley cliff, but also on the other cliff, in mixed evergreen and deciduous broadleaf forest, and in grassland as well as in evergreen broadleaf forest, with slope directions chiefly towards the west and the northeast. All three types of sites were used: cave, crevice, and pit, and only 38% were in a lower position. The main vegetation layer consisted of arbor + shrub and shrub + rock.

In undisturbed habitat, mean vertical distances from sleeping site to top and bottom of the cliff were 44.6 ± 38.0 and 120.4 ± 65.4 m, respectively. In disturbed habitat the corresponding distances were 8.4 ± 11.0 and 20.0 ± 9.9 m. For 4 monkey groups at the YTG, WJ, and LYY sites, the river was the only water source. At the XGB site, the two groups used seasonal water sources as well as the river (Fig. 1). The average distance from sleeping site to the nearest water source in undisturbed habitat (115.0 ± 86.8 m) was greater than in disturbed habitat (69.3 ± 42.5 m). The average number of food trees around sleeping sites in undisturbed habitat was lower than in disturbed habitat (4.2 ± 1.5 trees versus 7.4 ± 3.2 trees). The mean elevation of sleeping sites was similar in these two habitats (564.7 ± 151.7 m in undisturbed habitat, 544.1 ± 80.2 m in disturbed habitat), although frequencies were distributed differently for each category.
https://static-content.springer.com/image/art%3A10.1007%2Fs10329-010-0218-2/MediaObjects/10329_2010_218_Fig1_HTML.gif
Fig. 1

The distribution of sleeping sites of Francois’s langur within the study area in MYH NR

Selection of habitat factors

Due to a lack of sufficient data for groups at YTG and WJ sites, we analyzed selection of habitat factors only for groups at LYY and XGB sites. Table 1 demonstrates that all three groups preferred evergreen broadleaf forest and steep slopes as sleeping sites. For lyy group, the langurs strongly favored southwest, lower slope locations and lower elevations. For xgba group, slope direction appeared unimportant, whereas higher slope locations and elevations above 500 m were avoided. The xgbb group showed some differences compared with the other two groups, namely a tendency to avoid lower elevations while preferring higher elevations. They had no distinct preference for lower slope locations, preferring middle locations instead. Finally, as well as selecting evergreen broadleaf forest, they also slept in evergreen mixed forest.

All sleeping sites of lyy group were located on the river valley cliff. However, 29% of xgba group’s sleeping sites were not on the river valley, while this figure reached 50% for xgbb group. We found no seasonal water source nearby for sleeping sites located on the river valley cliff, whereas at least one was usually located near sites away from the river valley (for xgba group, r = 0.986, p < 0.001, n = 7; for xgbb group, r = 0.945, p < 0.001, n = 10).

Sleeping site selection in different seasons

Table 2 shows nights spent at different sleeping sites by the langurs in four seasons. Because we did not obtain yearly data on seasonal use of sleeping sites at the YTG and WJ sites, we only analyzed other data. Six sleeping sites were used by lyy group within a home range of 56 ha, 7 by xgba group in a home range of 78 ha, and 10 by xgbb group in a home range of 119 ha (Fig. 1). Four sleeping sites were used by both groups at the XGB site. Two sites were used throughout the year by lyy group, and 4 by xgba group; no site was found to be used in every season by xgbb group. The maximum number of consecutive nights on which a site was used was 6. Each group showed some variation in seasonal usage pattern of sleeping sites, but not significantly so (F = 0.209, p = 0.890, df = 3).
Table 2

Nights spent at the different sleeping sites by Francois’s langur in each season in MYH NR

Observation site

Sleeping site

Nights observed

Consecutive nightsa

Spring

Summer

Autumn

Winter

Spring

Summer

Autumn

Winter

YTG

1

0

3

0

0

0

0

0

0

2

0

2

0

0

0

0

0

0

3

0

2

0

0

0

0

0

0

WJ

4

2

0

2

0

0

0

0

0

LYY

5

6

3

0

0

6

2

0

0

6

0

0

1

0

0

0

0

0

7

0

0

2

2

0

0

2

0

8

2

0

0

0

0

0

0

0

9

2

1

3

3

0

0

0

0

10

2

6

5

6

0

5

4

4

XGB

11

2

1

2

2

0

0

0

2

12

6

1

3

1

6

0

2

0

13

1

11

5

2

0

5

5

2

14

3

3

2

4

2

2

0

4

15

0

0

0

1

0

0

0

0

16

2

0

0

2

0

0

0

0

17

1

0

0

2

0

0

0

0

18

1

0

2

6

0

0

2

2

19

2

3

0

0

2

2

0

0

20

1

0

1

0

0

0

0

0

21

2

1

0

0

2

0

0

0

22

1

2

0

0

0

2

0

0

23

2

0

0

0

2

0

0

0

Total

 

38

39

28

31

20

18

15

14

aTwo or more nights

Food availability in two habitats

A total of 265 points was established in undisturbed habitat, and 206 points in disturbed habitat. We recorded 342 species of trees and a total of 44 food species consumed by Francois’s langur in undisturbed habitat, and 249 tree species and 32 food species in disturbed habitat. Twenty-four food species were shared in both habitats.

The basal areas of leaf-food trees and flower-food trees were higher in undisturbed habitat (0.47 and 0.07 cm2/m, respectively) than disturbed habitat (0.33 and 0.05 cm2/m, respectively), and wild fruit production was also higher in undisturbed habitat (0.09 g/m) than disturbed habitat (0.06 g/m). In contrast, plantation area of crop fruit was higher in disturbed habitat (33.54 ha) than undisturbed habitat (5.80 ha). Food availability varied dramatically across different habitats (χ2 = 1.441, df = 3, p < 0.001).

Entering sleeping sites

The langurs entered sleeping sites at 18:00–20:00 in spring and summer (n = 60) and 17:00–19:00 in autumn and winter (n = 56). Usually, they moved rapidly along in the undergrowth to the sleeping site, but they occasionally appeared in the nearby crown layer. They always spent about 30 min resting, grooming or feeding within a radius of around 10 m from the sleeping site before entering the site. These activities were performed silently. It took an average of 7 min (range 5–16 min) to occupy a sleeping site.

Discussion

Avoiding predators

Of the factors influencing sleeping site selection, predator avoidance might be the most important (Liu and Zhao 2004). This appears to apply to Francois’s langur in different habitats. First, regardless of habitat, Francois’s langurs selected rock caves, crevices or pits as sleeping sites, all located on slopes with ≥60° gradient. As well as sheltering the monkeys, such sites were inaccessible to predators (Hamilton 1982; Huang et al. 2003). Second, in both habitats, distances from sleeping site to the top and foot of the cliff were all sufficiently large to make access difficult for predators. Third, the langurs remained silent as they moved rapidly to their sleeping sites at dusk; this inconspicuous presleeping behavior probably helped to reduce the risk of being detected by predators (Heymann 1995). In addition, in undisturbed habitat, the main vegetation layer around sleeping sites was shrub + rock, not full shrub or arbor + shrub; this provided an open visual field, preferable in some situations for allowing early detection of predators (Treves 2002). The cliff as a safe refuge was also shown in a study of baboons (Hamilton 1982); from the point of view of safety it was followed by emergent trees, closed canopy trees, and open woodland trees.

During our study one eagle that hovered near the lyy group was a potential predator of young monkeys (Reichard 1998), but we observed no attacks, and the monkeys did not alarm call or show mobbing behavior in response to it. No traces of other natural enemies, such as leopards or jackals, were observed by us or by local people. Local people do not kill the monkeys due to conservation efforts by the NR staff. In view of these factors, returning to sleeping sites that provide protection from predators may at least partly reflect cultural traditions (Nishida 1987), having developed in the past under heavy predation pressure (Liu and Zhao 2004).

Food resources

The area around the sleeping site was observed to be the first or last forage site in both habitats, but food tree frequency was lower in undisturbed habitat. Additionally, the average time spent foraging around the sleeping site was less in undisturbed habitat (9.02 ± 1.32% of the full-day feeding time) than disturbed habitat (20.05 ± 13.45%) (Wang, unpublished data). These differences may be related to food availability and distribution across habitats. In undisturbed habitat, sufficient wild food in the home range may meet the nutritional demands of the langurs, so it may be unnecessary for the monkeys to consider food availability when selecting a sleeping site. However, in disturbed habitat with less wild food available, the langurs enlarged their home range and increased foraging time (Luo et al. 2005; Wang 2008), and the area around the sleeping site became a foraging location. This requires less energy expenditure than long foraging journeys (Chapman et al. 1989; Richard and Robert 1999) and maximizes foraging efficiency (Chapman 1989; Fan and Jiang 2008). Although crop fruit was more abundant in disturbed habitat, seasonal fluctuations in availability and local people’s protection of farmlands against the monkeys decreased their contribution to the monkeys’ overall food intake.

Besides differences in food availability across habitats, there were differences in food resource distribution. At the YTG and WJ sites, food was distributed continuously. In the home ranges of lyy group, xgba group, and xgbb group there were 3, 8, and 10 patches of food, respectively (Wang 2008). When food resources are patchy, the langurs often need to traverse barriers such as roads, villages, farmland, and grassland to continue foraging; this requires increased energy expenditure and alertness. In some cases the langurs failed to cross these barriers due to human disturbance, which usually resulted in increasing foraging around sleeping sites. Food resource around sleeping site also played an important role in bad weather. For example, on one rainy day foraging by the xgba group around the sleeping site lasted 1.7 h, accounting for 41.23% of that day’s feeding time (Wang, unpublished data).

Food resources may influence the role of other factors. For example, in disturbed habitat, more food trees was associated with arbor + shrub around sleeping sites; low and patchy wild food availability increased the number of foraging sites and enlarged home range size, which led to sleeping sites being located not only in evergreen broadleaf forest but also in evergreen broadleaf and deciduous broadleaf mixed forest and grassland.

Therefore, food resources may be one factor determining Francois’s langurs’ selection of sleeping sites, especially in disturbed habitat. Although more food trees around sleeping sites decreased visibility, this does not appear to increase danger, in view of the extinction of natural enemies and the absence of hunting by humans. This strategy recalls that of common marmosets (Callithrix jacchus) in highly disturbed urban fragments; i.e., when potential predators have been eliminated, food availability is the main determinant of the marmosets’ sleeping site selection (Mendes Pontes and Soares 2005).

Water resources

Sleeping sites may also be selected in relation to water resources (Chapman 1989). In Guangxi, Huang et al. (2010) did not record Francois’s langurs drinking from the ground, and suggested that liquid from food was their only source. However, in Guizhou, Francois’s langurs were observed to drink from the river before entering sleeping sites (Li 1994). This difference may be related to surface water distribution in these two habitats: there was almost no surface water in the former habitat, whereas in Guizhou, of all sites where Francois’s langur inhabit, 80% of them are river valley (Li 1994). We found that the langurs drank every 1–2 days, not only from the river, but also from seasonal water sources such as ponds and gullies. In undisturbed habitat, the langurs only drank from the river during normal day ranging; water did not appear to influence sleeping site selection. In disturbed habitat, when the langurs ranged in the river valley, they drank while traveling; however, when they spent the night away from the valley, they came out and drank nearby after arriving at the site. There was strong positive correlation between sleeping sites away from the river valley and nearby seasonal water sources. Moreover, those sleeping sites were rarely used in the case of water shortage. So, in disturbed habitat with reduced wild food availability, water may be a factor when selecting sleeping sites at a distance from the river.

Other factors related to sleeping site selection

Intergroup competition may sometimes impact on sleeping site selection (von Hippel 1996; Reichard 1998). xgba and xgbb groups derived from a larger group which fissioned just before our study. The overlap area of their annual home ranges reached 32 ha (Wang 2008), with 4 shared sleeping sites. We recorded 17 intergroup encounters at distances of 20–100 m, of which only one involved competing for a sleeping site. Reichard (1998) suggested that occupancy of sleeping sites is primarily mediated through order and timing of retreat to a site. In our study, some separations appeared based on use of different habitat categories by the groups (Table 1); for example, half of xgbb’s sleeping sites were in evergreen mixed forest, whereas xgba group avoided this vegetation type, which may lead to decreased competition for sleeping sites.

Accumulation of excreta might be another factor influencing reuse of sleeping sites, due to the risk of parasitic contamination (Hausfater and Meade 1982); to reduce this, primates should avoid recently used sleeping sites (Hausfater and Meade 1982; Heymann 1995; Kowalewski and Zunino 2005). Francois’s langurs had fixed excretion sites at sleeping sites, which may reduce contamination (Anderson 1998). The number of consecutive nights on which a sleeping site was used was 2–6 by the langur (Table 2). Therefore we concluded that on some cases the langurs used a site for several consecutive nights, i.e., they did not avoid the same sleeping site for several consecutive nights .

Acknowledgments

This research was funded by the Ministry of Science and Technology, P. R. China (Grants No. 2008BADB0B01). All research methods adhered to Chinese legal requirements. We are grateful to the staff of Mayanghe National Nature Reserve for their support and help. We thank Mr. Qikun Zhao, Dr. William Bleisch, and Mr. Paul Insua-Cao for their valuable comments and revisions of English. We are grateful for the meticulous work of the anonymous editors. We are also indebted to Ms. Xiao Yanqing and Dr. Xing Shaohua for their help in providing valuable references. Thanks are also given to the anonymous reviewers for their very useful and detailed comments.

Copyright information

© Japan Monkey Centre and Springer 2010