 Reference Base  The Javan rhinos, Rhinoceros sondaicus annamiticus, of Ca... |
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| Location: |
Asia - East Asia - Vietnam |
| Subject: |
Ecology - Census Methods |
| Species: |
Javan Rhino |
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For the rhino survey, standard tracking analysis methods were used consisting of three components:
a. establishment of the current range by surveying a wide area for any signs of rhinos,
b. track analysis by measuring footprints encountered and making plaster casts in order to identify individual rhinos based on foot measurements and front hoof measurements to estimate the minimum number of rhinos in the area, and
c. extrapolation for areas not covered in the track analysis but within the rhino range in order to estimate a maximum number of rhinos in the area.
The survey was carried out over a period of one month by two teams, consisting of six people each .Each team had one person dedicated to take all measurements in order to avoid errors, which could occur if more than one person was involved in taking the measurements. Geographical coordinates were taken for every measurement. Data were recorded on a standard sheet and included length and width of footprint and length and width of front hoof for every good quality footprint encountered and observations on other signs such as droppings, grazing signs, saltlicks, etc. The total length of investigation lines was around 218 km, with some lines repeated several times. The survey team collected data on wallows (12), dung (6), salt licks (2), footprints (241 of which 137 plaster casts were made) and other signs such as traces of bodyrubbing on tree trunks and traces of eaten and broken plants and trees.
The total number of plaster casts used for the analysis was 144 of which 137 casts were made during the survey in January 1999 and 7 casts just prior to the survey in December 1998. Of the 144 casts, 33 could not be analysed because of poor quality; the other 1 1 1 were carefully analysed in the laboratory. Also the dimensions of 241 measurements taken in the field were included in the analysis. The width and length of all the footprints and front hooves were recorded.
Based on dimensions of the casts, the dimensions of the field measurements and differences in forms, the plaster casts were divided into groups, each group with the same characteristics in form and size. In this manner individual rhinos were recognised (Dang and Khanh, 1999). The plaster casts and other raw data are kept at the headquarters of Cat Tien National Park.
The field and analysis methods used for the survey were similar to the ones used during the April 1998 census carried out under the auspices of the International Rhino Foundation and the IUCN/ SSC/ Asian Rhino Specialist Group (Sung et al,, 1998). Methodologies used during both these surveys follow the procedures developed by van Strien (1986) in Gunung Leuser National Park, Sumatra, Indonesia during his work on the Sumatran rhino. The April 1998 survey was carried out during the dry season while the January 1999 survey was conducted just after the rainy season.
Automatic camera trapping
The two rhino surveys provided a detailed understanding of the locations within their range where the rhinos come frequently. This information combined with suggestions from local people was used to install ten automatic photo camera sets in the area. The sets are made by Trail Master, a company based in the US.
One set consists of an infrared transmitter, an infrared receiver and a modified compact camera. Whenever the infrared beam is interrupted, the receiver gives a signal to the camera, which is then triggered. Sensitivity of the receiver and the interval time between pictures can be adjusted. Sensitivity is measured in pulses of 0.05 seconds each. The receiver records every event in which the infrared beam is interrupted, even if the interruption is of less duration than the set sensitivity. Therefore, the number of pictures taken is usually lower than the number of events recorded. As
falling leaves, extremely big raindrops and insects attracted by the infrared transmitter can also trigger the camera, not all pictures taken have the targeted species on them. Table 2 provides some of the basic settings of the cameras used in Cat Tien National Park,
For every camera the following information is kept on record: geographical location, dates in the field for every location, dates of change of film and batteries, dates and times of pictures taken, dates and times of events and contents of pictures.
Preliminary results of the on-going camera trapping exercise
It is with the last observation in mind that the WWF-Cat Tien National Park Conservation Project decided to execute a camera trapping exercise in the Park. It is hoped that enough pictures of rhinos can be taken so that individuals can be recognised and related to footprint sizes and shapes. Thus critically important information on the population's sex and age structure bright be obtained.
Ten cameras were installed at ten dilterent locations within the rhino range of 6,500 ha in the week of 26 April to 2 May 1999. Within two weeks the first pictures of rhinos were taken . These are believed to be the first-ever pictures taken from life of R. s. annainiticus. Having these pictures assists scientists to make a step ahead in learning more about this secretive animal. The seven pictures taken so far are depicted on pages 42 and 43. They originate from three different locations and the time at which the pictures were taken indicate that the.animals are most active during the night.
Photo 1 shows a rhino (rhino 1) where a height-marker is visible behind the animal, just in front of its ears. The height of the marker is one meter (32 mm on the picture, about 40 mm at rhino's shoulder when accounted for perspective). The height at the shoulder of this individual is estimated to be 130 cm (52 mm on the picture/40 mm) which is slightly larger than the estimate presented (110- 120 em) by Sung et al. (1 998).
Sung et al. (1998) estimate that the R. s. annamiticus is about 75 to 80% of the size of a R. s. sondaicus. They base this estimate on the ratio of the width of the hind feet measured in Cat Loc (20-23 cm) versus those recorded in Ujong Kulon (25-28 cm). Using this relation in size and estimating the weight of a R. s. sondaicus to be 1,600 kg, it may be estimated that a R. s. annamiticus weighs about 650 to 800 kg (1,600 kg x 0.753 to 0.83).
Discussion
The small size of the footprints from Cat Loc is more in accordance with the size of footprints of Sumatran rhinos (Dicerorhinus sumatraensis) or with sub-adult R.s. sondaicus (Sung et al., 1998). Since all footprints from Cat Loc are between 20 and 23 cm in width, it would be hard to conclude that the Cat Loc population consists only of subadults. From the pictures presented in this article it is beyond doubt that the Cat Loc rhinos are Javan and not Sumatran rhinos. Sung et al. (1998) argue that the poor quality of the habitat in Cat Loc may have contributed to the smallness of R.s. annainiticus and that the Ujung Kulon and Cat Loc populations belong to clearly distinct gene pools. To stress this point, they also suggest for R.s. annamiticus the vernacular name 'Vietnamese rhino' instead of using the tenn 'Javan rhino' in Vietnam.
Looking at the locations, dates and times that the pictures were taken, combined with the fact that adult Javan rhinos are generally regarded as solitary animals, an attempt can be made to deduct whether the pictures are all of the same or of different individuals. The rhinos on photos 1 and 2, 3 and 4, 6 and 7 are almost certainly of the same individual (each pair of pictures has been taken at the same place and very shortly after each other). Hence it is deducted that all pictures are of at most four different individuals (including the possibility that all pictures are of the same individual).
Referring to camera trapping of Javan rhinos in Ujong Kulon, Griffiths (1992) describes eight parameters with which individual rhinos could be recognised: size, horn shape, eye-wrinkles, neck folds, skin pores, scars., neck plate profile and cheek profile.
The size of the animals in the pictures where a height marker is visible, is roughly the same. Although differences in perspective make estimates difficult, the rhino in the wallow also seems to be about the size as the others. It is clear that on the basis of the available pictures one cannot differentiate individuals by their size.
The shape of the horn of rhino 5, 6 and 7 looks rather similar; not sharp but somewhat flattened on the top. The shape of the horn of rhino 1, 2, 3 and 4 is more pointed. Although this characteristic could indicate that the available pictures belong to two individual rhinos, evidence seems to be too crude to build upon.
The eye-wrinkles of rhino 5, 6 and 7 look more oval than the others, which seem to be more round. Using this characteristic, one could again argue there are two different individuals on the picture.
The neck folds, neck plate profiles and cheek profile look in general similar. Using this characteristic seems unworkable because differences in position of the head relative to the body, differences in pose and differences in positioning of the camera result in differences in appearance of details in the folds. Patterns in skin pores cannot be recognised clearly in these pictures. From the limited part of the body visible and the mud on the animals, no obvious marks or wounds are visible.
The sex of the animals in the pictures cannot be seen and there are no calves who usually join their mothers.
Griffiths (1992) recognising 31 individual Javan rhinos in Ujong Kulon, 60% of which the sex was known, notes that all individuals confirmed to be male have a horn, while all individiials confirmed to be female have no horn. Amman (1985) concludes that female Javan rhinos in Ujong Kulon have at most a small 'hump' and exceptionally a 'small horn'. Schenkel and Schenkel-Hulliger (in Amman, 1985), however, observed that all the rhinos they saw in Ujong Kulon had a distinctive horn and assumed that at least some of them must have been female. Whether or not female Javan rhinos from Ujong Kulon have a small horn or a hump remains unclear. The horn in the pictures of the rhinos from Cat Tien National Park are not large but seem to be too large to be, subjectively, classified as 'hump' or 'small horn'.
The rhino on Photo 4 (rhino 4) has its mouth wide open. A large incisor in the lower jaw is clearly visible. Van Strien (pers. comm.) believes that having large incisors is typical for male Javan rhinos.
Based on the above the following tentative conclusions can be drawn:
1. the pictures confirm that the Cat Lee rhino population consists of Javan rhinos and not Sumatran,
2. the Cat Tien National Park rhinos are most active during the night,
3. the pictures are of 1, 2, 3 or 4 different individuals,
4. all pictures are of adult rhinos,
5. at least rhino 1 and probably rhino 3 and 4 are males,
6. it is unlikely that there is a female individual on any of the pictures,
7. the pictures confirm that R.s. annamiticus is between 75 and 80% of the size of R.s. sondaicus, and
8. R.s. annamiticus is between 110 and 130 cm high at the shoulder and weighs between 650 and 800 kg.
Perhaps, at this stage of the exercise, it is more important to conclude that it requires large numbers of pictures and detailed analysis to be able to recognise individual Javan rhinos using camera traps, if possible at all. Nevertheless, any piece of information is welcome in getting to know this elusive animal better.
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