Estimating the population structure of Javan rhinos (Rhinoceros sondaicus) in Ujung Kulon National Park using the markrecapture method based on video and camera trap identification

Abstract

The population structure of the Javan rhino (Rhinoceros sondaicus) in Ujung Kulon National Park (NP) in Banten, Indonesia was assessed using visual identification and mark-recapture estimation. The software program CAPTURE was used for selecting the best fit estimator for the mark-recapture calculation and yields M(th) as the best model. The software results delivered a mean estimation of 32 rhinos (a minimum of 29 and maximum of 47 rhinos) with a 95% confidence level based on the dataset obtained from April 2008 to September 2009. The visual identification suggests that the current population in Ujung Kulon NP is male biased by a 3:2 sex ratio of males versus females. The demography shows that the population consists of mainly adult individuals that have a tendency of 1% population growth per year.

Full text

90 Pachyderm No. 49 January–June 2011
Estimating the population structure of Javan rhinos (Rhinoceros
sondaicus) in Ujung Kulon National Park using the mark-
recapture method based on video and camera trap identification
Adhi Rachmat Sudrajat Hariyadi1*, Agus Priambudi2, Ridwan Setiawan3, Daryan Daryan4,
Asep Yayus5 and Hendra Purnama6
1,3WWF Indonesia, Jl Halmahera No. 9 Villa Admiral Lippo Carita km 8, Labuan-Pandeglang 42264, Banten,
Indonesia
2,4,5,6Ujung Kulon NP Authority, Jl Perintis Kemerdekaan No. 51 Labuan – Pandeglang Banten Indonesia 42264
*Corresponding author: ahariyadi@cbn.net.id
Abstract
The population structure of the Javan rhino (Rhinoceros sondaicus) in Ujung Kulon National Park (NP) in
Banten, Indonesia was assessed using visual identication and mark-recapture estimation. The software pro-
gram CAPTURE was used for selecting the best t estimator for the mark-recapture calculation and yields
M(th) as the best model. The software results delivered a mean estimation of 32 rhinos (a minimum of 29
and maximum of 47 rhinos) with a 95% condence level based on the dataset obtained from April 2008 to
September 2009. The visual identication suggests that the current population in Ujung Kulon NP is male
biased by a 3:2 sex ratio of males versus females. The demography shows that the population consists of
mainly adult individuals that have a tendency of 1% population growth per year.
Key words: Javan rhino, population, mark-recapture, population estimation, camera trap
Résumé
La structure de la population du rhinocéros de Java (Rhinoceros sondaicus) dans le parc national d’Ujung
Kulon à Banten en Indonésie a été évaluée en utilisant l’identication visuelle et une estimation de capture-
marquage-recapture. Le logiciel CAPTURE a été utilisé comme le meilleur modèle pour sélectionner le
meilleur estimateur propre au calcul et aux rendements M (th) de capture-marquage-recapture. Les résultats
du logiciel ont donné une estimation moyenne de 32 rhinocéros (un minimum de 29 et un maximum de 47
rhinocéros) avec un niveau de conance de 95% d’après la série de données obtenues d’avril 2008 à septem-
bre 2009. L’identication visuelle suggère que la population actuelle dans le parc national d’Ujung Kulon
est biaisée en faveur des mâles avec un rapport de 3 mâles contre 2 femelles. La démographie montre que la
population se compose principalement d’individus adultes qui ont une tendance de croissance de 1% par an.
NOTES

Pachyderm No. 49 January–June 2011 91
Introduction
The main indicators of success in conserving an en-
dangered wildlife species are the population size and
the net population growth. The Indonesian govern-
ment set the growth of the Javan rhino population at a
rate of 3% annually in order to achieve the conserva-
tion goal set in the Indonesian Rhino Conservation
Strategy (PHKA, 2007). Unfortunately, the existing
condition of the habitat (dense forest) and the scarce
distribution Javan rhinos do not allow the application
of census methods to obtain exact counts such as those
like direct counts, which can be implemented for deer
and pheasants (Lewis, 1970), or using aerial counts
as done for wildlife in the Serengeti-Mara region
(Talbot & Stewart, 1964). Fortunately, the distribu-
tion of Javan rhinos has been extensively studied
(Hoogerwerf, 1970; Muntasib, 2002), so there is no
immediate need for conducting a patch occupancy
survey, which would tend to have a bias due to the
inability of this method to accurately detect the pres-
ence of an animal in a given survey area if not done
repeatedly (Mackenzie & Royle, 2005). Due to the
difculties in applying a direct count/exact count,
the existing conditions for Javan rhinos should only
rely on a relatively accurate estimation of population
structure, instead of on exact counts.
One method that offers relatively accurate
population estimates of wildlife species is the mark-
recapture calculation based on visual identication, as
done on tiger populations in India (Karanth & Nichols,
2002). The use of camera traps for visual identication
of rhinos in Ujung Kulon NP was initiated by Grifth
(1993), and was followed by Yahya (2002) to study the
distribution and by Hariyadi et al. (2010) to study the
behaviour of the Javan rhinos directly in their habitat.
The Javan rhino is known to have frequent
wallowing behaviour because moisture/water is
required to ensure the integrity of their epidermis
(Shadwick et al., 1992), as well as for thermoregulation
(Schenkel & Schenkel-Hullinger, 1969). Failure to
wallow will lead to dryness that could eventually lead
to pathological conditions and pain in the epidermal
tissue (Munson et al., 1998). The need to wallow for
both male and female Javan rhinos in Ujung Kulon
NP is indicated by the daily wallowing behaviour
recorded in previous observations (Schenkel et al.,
1969; Hoogerwerf, 1970; Sajudin, 1984). There is
no known sexual dimorphism in the epidermal tissue,
and no differences in wallow frequencies between
male and female Javan rhinos have been reported.
The differences of wallow frequencies between males
and females are assumed to be very little based on
ndings from Yahya (2002), so they should show
similar wallowing frequencies and probabilities. If
this is true, there will not be a sex bias to take into
account with the survey design.
In using mark-recapture estimation of the
population size, it is important to determine the
population closure during the survey period.
Population closure is dened using two categories—
the demographic closure and the geographic closure
(White et al., 1982). Since the movement trends
of Javan rhinos have been previously recorded in
Yahya (2002) and Setiawan and Yahya (2002), the
geographic closure for the Javan rhino population
can be dened. However, due to the occurrence of
births and mortality during the survey period, the
demographic closure principles may not be fullled in
this study (White et al., 1982), so the analysis must be
carefully designed to ensure that demographic closure
is accounted for in order to select the appropriate
model for mark-recapture estimation.
Material and methods
Estimation of Javan rhino population size using
mark-recapture calculation requires identication of
each individual rhino. Considering the difculties of
physically capturing and marking each rhino, it is
agreed that the less invasive method to calculate is
through individual identication and differentiating
Javan rhinos from photos and/or video. The use of
automatic video recording devices (video traps) is an
approved method for estimating the population size of
the elusive species (Karanth & Nichols, 2002) such as
Javan rhino. Therefore, 34 DVREye automatic record-
ing devices were used for this purpose in the peninsula
of the Ujung Kulon NP from April 2008 to September
2009. Rhino habitat in Ujung Kulon NP consists of
a peninsula of 30,000 ha that is dominated mainly
by lowland rainforest, coastal and mangrove forest.
These 34 cameras were systematically placed
in the study area and 1 camera was placed in the
vicinity of holes at the height of 1.5 to 2.5 metres
above ground. These cameras were secured onto a
tree with 10 to 20 degree downward angles to record
any activity in the wallow hole. Wallow holes were
selected using several criteria such as: type of wallow
holes (temporary or permanent), the numbers of
rhinos known to use a particular hole and the size
of the wallow (area in m2 and the depth of water
Estimating Javan rhino population in Ujung Kulon National Park

92 Pachyderm No. 49 January–June 2011
and mud). Camera placement was mainly focused
on permanent wallows that were utilized by one or
more rhinos, while the area and depth of the wallow
holes were brought in as supporting information used
to categorize the wallow types. Selection of wallow
holes (camera spots) was made based on a grid system
to ensure geographical representation of the rhinos
whereby one wallow was selected within each sector
of the grid and only one camera was placed at each
wallow. Based on rhino movement and home range
of 1.4 to 3.8 km per day (Muntasib, 2002), the survey
area was divided using grids of 4 km2 to cover the
distance that rhinos travel every day. These grids
divided the known rhino habitat of the peninsula into
50 grid squares; 35 out of these 50 grid squares were
then selected based on the high rhino occurences
recorded in a previous study (Muntasib, 2002; Yahya,
2002). The video trap camera placement locations are
shown in Figure. 1.
Based on previous observations of Javan rhino
behaviour by Yahya (2002), it is safe to assume
that female and male Javan rhinos wallow at
approximately the same frequency; thus the camera
placements still allow all individuals to have a non-
zero probability of capture. This was further assessed
by comparing recapture rates of males and females.
The survey was conducted within a 10-year period to
ensure that the survey covered twice the length of the
rhinos’ reproductive cycle, as mentioned in Hariyadi
et al. (2008). The reproductive cycle was estimated
at 3 years with additional 2 years for mother-calf
afliation period; therefore, the period of 10 years
should represent 2 repetitions of the reproductive
cycle within the population. It is also safe to assume
that geographical closure is met, as no rhinos migrated
into or out of the rhino habitat during the survey. The
camera coverage (sample area) also represents the
known rhino home ranges based on Muntasib (2002)
and Yahya (2002); thus the areas without known
rhino home ranges were not sampled. Since there
are no migrations of rhinos into or out of the survey
areas, we conclude that migration does not violate
the demographic closure set up in the survey design.
However, the closure assumption will be tested using
Figure 1. A map of Ujung Kulon peninsula showing the sampling grid representing the known geographic
locations of the Javan rhinos.
Hariyadi et al.

Pachyderm No. 49 January–June 2011 93
CAPTURE software (White et al., 1978) to determine
the most suitable model for estimating the population
of the Javan rhinos.
Each colour represents one of three teams assigned
to installing the video trap camera equipment. These
video traps were placed to record rhino activities in
the selected wallow holes for 15 to 20 days at the
same locations. The installment date was marked by
assigning a person to walk in front of the camera while
holding a signboard containing the date to be recorded,
and the camera trap removal/data retrieval date was
marked in a similar manner. The period between the
installment and data retrieval dates was dened as a
survey period. Each of these survey periods represents
an ‘occasion’, which is the parameter repeated in the
calculation of mark-recapture.
Individual marking and identification were
done by observing and comparing morphological
features and using parameters developed by Grifth
(1993). This method relied on indicators such as:
horn shape and size, neck and eye folds, ear shape,
footprint size, as well as distinct features (scars, birth
marks) to differentiate individual Javan rhinos. At
least three parameters must be employed to make
a positive differentiation among individual rhinos
captured in the photos, while other morphological
features (scars, necks, neck folds, etc.) are used for
detailed differentiation among individuals found
within approximately the same habitat range, or
individuals within the same age class or sex. Special
attention was given to very young calves travelling
with their mothers, as they may indicate recent births.
The calves’ ages were estimated using a comparison
of body size between the calves and their mothers.
Calves estimated at 1 or 1.5 years-old that were not
sighted in the previous surveys would be categorized
as newborn. All newborn rhinos were tabulated for
calculating the birth rate of the population. Examples
of the differentiation method are presented in Fig.
2 and 3. Each identied rhino will be given a code
according to the sex, age group (calf, subadult, adult),
grid number where it was rst recorded and a unique
individual number to differentiate rhinos that may
be detected in the same grid square. With this code,
each individual rhino can be recorded, identied
and re-identified on different occasion(s). Each
video clip with rhino footage was analyzed using a
computer capable of running the VLC media player
programme, a software that allowed for considerably
accurate identication of rhinos based on visual and
morphological features mentioned above.
In addition to the individual identification
parameters described above, the rhinos were classied
into four different age classes based on their overall
body and horn size. The rst category consists of adult
rhinos; both male and female rhinos must have a horn,
though that of the male is typically larger. The second
category consists of subadults with relatively smaller
bodies and horns. The third category represents
calves with very small bodies—normally without
any distinct horn, and most of their time is spent with
their mother.
Analysis was done by identifying, marking
(coding) and recording each rhino that was captured
on video within the survey period (occasion). Rhino
data collection was implemented from April 2008 to
September 2009 to ensure demographic closure. In
May, June and September 2008, as well as February
and April 2009 video trap devices were not operated
due to maintenance and repair. Calculation for the
Javan rhino population estimate was performed using
the Lincoln–Peterson formula and using CAPTURE
software (White et al., 1978), which were known
to deliver accurate mark-recapture calculations. To
comply with the CAPTURE software requirements,
rhino detection was represented in a binary system,
whereby ‘1’ marks presence and ‘0’ marks absence
during each occasion. Data was processed using
analysis pattern x-matrix with a statistical population
estimation at 95% confidence level. Minimum
numbers of rhinos were determined by identifying
individual Javan rhinos that were recorded until
September 2009.
In order to study the population trend for the
past 10 years, results from this year’s analysis were
compared to those of 2000, 2004 and 2009, which
were analysed in the same manner by WWF and
Ujung Kulon NP authorities using the same camera
locations from January to December in each year, but
using different brands of cameras. This comparison is
expected to illustrate the population structure in 2000,
2004 and 2009, as well as describe the differences that
may have occurred (differences in age structures and
sex ratio that might indicate population dynamics).
All births from 2000 and 2009, with the addition of
records from 2010, as well as mortality (based on
ndings of rhino carcasses or remains) were put into
a table to calculate the actual population growth of
Javan rhino in Ujung Kulon NP. Surveys in 2000,
2004 and 2009 were conducted regularly every
month, so birth ndings should represent the actual
population trend. However, rhino deaths may not
Estimating Javan rhino population in Ujung Kulon National Park

94 Pachyderm No. 49 January–June 2011
reect the actual mortality rate, as all mortality nds
were opportunistic.
Results
Throughout the survey periods, 27 rhinos were
identied using CAPTURE (White et al., 1978).
Examples of identication and marking of the Javan
rhinos are shown in Fig. 2 and 3. These rhinos and
their occurrences in each occasion are summarized
in Table 1. Recapture rate of females is 0.15 while
that of males is 0.17. The calculated closure analysis
values (Z=-2.533 and P=0.00565) suggest that the
closure assumption is violated. Further calculations
for model selection using CAPTURE software’s
‘Goodness of Fit’ models resulted in the 1.00 criteria
for M(th), suggesting that it is the best suited estimator
for mark-recapture, given the capture trend from the
dataset. The M(th) model calculates a mean estimation
of 32 rhinos with a standard error of 4.2381. Further
analysis shows that with 95% condence level it can
be ascertained that the Javan rhino population during
the survey period of June–September 2009 was be-
tween 29 to 47 rhinos. The Lincoln-Peterson formula
calculation, using data from the same survey period
to enable comparison between the two estimation
methods, reveals the mean of 41 individual rhinos
with standard error of 19.07, while manual identica-
Figure 2. The video capture equipment enabled the team to identify adult rhinos by the presence of the horn
in the male (B) and lack of distinctive horn in the female (A). Differentiating sex using horn presence can only
be applied for rhinos within the same age class (subadult or adult).
Figure 3. It is possible to differentiate rhinos based on the horn shape as a primary parameter. Note the blunt
horn (cone type) on the male rhino in B, while the male in A has a sharper (funnel type) horn tip (white arrows).
The rhino in B has a rounded jaw and longer prehensile (upper) lip while the rhino in A has a ‘square’ jaw as
indicated with a black arrow. Male A has continuous neck folds with no skin protrusions, while male B has
broken neck folds with conspicuous protrusions downwards from the neck (marked with a dotted oval).
A
A
B
B
Hariyadi et al.

Pachyderm No. 49 January–June 2011 95
Figure 4. Pie chart showing the composition of males
and females in the Javan rhino population surveyed
between April 2008 to June 2009.
Figure 5. The age structure of Javan rhinos in the
peninsula of Ujung Kulon NP surveyed from April 2008
to July 2009. The large percentage of calves indicates
th e breeding capability of this population.
Estimating Javan rhino population in Ujung Kulon National Park
Table 1. Summary of Javan rhinos identied through video trap implementation between April 2008 and
September 2009, with observation periods (occasions) represented by the months. Individual detection on
each occasion is marked as ‘1’, while no detection is marked as ‘0’
ID Rhino Apr Jul Aug Oct Nov Dec Jan Mar May Jun Jul Aug Sept
FADUB1401 0 0 1 10 0 010 100 0
M,Cal,B14,2 0 0 1 10 0 010 100 0
FADUB1403 0 0 0 10 0 000 000 0
FADUB2604 1 0 1 00 0 000 000 0
MCalB2605 1 0 1 00 0 000 000 0
FADUB2606 1 1 0 00 0 000 000 0
FADUB4407 0 0 0 00 0 110 000 0
FADUB5208 1 0 0 00 0 001 001 0
MSADB5209 1 0 0 00 0 000 000 0
MCal B5210 1 0 1 01 0 000 0 01 0
FADUB5211 0 0 0 01 0 000 100 0
MADUB5212 0 0 0 00 1 000 011 0
MADUB5513 0 0 0 00 1 000 010 0
FADUB5614 0 0 0 00 0 010 000 0
MCal B5615 0 0 0 00 0 010 0 00 0
MADUB3516 0 0 0 00 0 010 110 1
MADUB2117 0 0 0 00 0 010 110 0
MSADB2018 0 0 0 00 0 000 100 0
MADUB3519 0 0 0 00 0 000 110 0
MADUB3520 0 0 0 00 0 000 010 0
MCalB5221 0 0 0 01 0 000 010 0
FADUB4522 0 0 0 00 0 000 000 1
MADUB5723 0 0 0 00 0 000 000 1
MADUB5024 0 0 0 00 0 000 001 0
FSAB1725 0 0 0 00 0 000 010 0
FADUB1726 0 0 0 00 0 000 011 1
MCalB1727 0 0 0 00 0 000 011 1

96 Pachyderm No. 49 January–June 2011
tion from video footage yields 27 individual rhinos.
There were a total of 11 females and 16 male
rhinos identied from video capture, resulting in a
female to male sex ratio of 2:6 (41% females and
59% males), as shown in Fig. 4, while there are 18
adults, 3 subadults and 6 calves as shown in Fig. 5.
This result (2009) is compared with the results
from 2004 to study the population dynamics and show
the population composition over time (Fig. 6). The
comparison shows that the sex ratio does not differ
Figure 6. Comparison of
Javan rhino’s sex ratio (A)
and age composition (B).
The sex ratio recorded in
2004 and 2010 is consistent,
while there is an increase of
of adults and calves from
2004 to 2009.
Table 2. Compilation of birth ndings recorded from camera/video trap implementations from
2000 to 2010 with mortality based on carcass ndings throughout the period
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010
Birth 2 3 4 32
Mortality 111 1 11 3
Hariyadi et al.

Pachyderm No. 49 January–June 2011 97
much between 2004 and 2009, but there is a difference
in the age structure of the population between these
periods of observation.
In order to study the population trend based on
birth rate (derived from camera trap and video trap
identications) and mortality rate (based on nding
of carcasses and remains etc.), all data from 2000 to
2009 were compiled and shown in Table 2. Based
on this data, the average birth rate is 1.4 births per
year (Standard Deviation: 1.5776), and the average
mortality rate is 0.9 deaths per year (Standard
Deviation: 0.8755) (Fig. 7).
Discussion
Estimating the population of the Javan rhino using the
mark-recapture technique can be applied as an option
that is less invasive and possibly more discriminative
than the existing footprint count method. However,
this method relies on the accuracy of identication and
differentiation of individual rhinos as a prerequisite.
Detection of false positives will yield an inaccurate
estimation from the CAPTURE software, so photos
of individuals that cannot be identied cannot be used
for such analysis. Both the Lincoln-Peterson formula
and CAPTURE software will only yield accurate
results based on the accurate identication of rhinos
from photos and videos. Three-way identication
(identication made and agreed by three persons) is
considered as a valid evaluation procedure.
Similar recapture rates of females and
males (0.15 and 0.17 respectively) suggest
that sex bias using camera observation
due to differences in wallow frequencies
between male and female is negligible. When
comparing the results from CAPTURE and
Lincoln-Peterson, it is noted that there are
differences in standard error values that may
be attributed to the accuracy of each formula.
CAPTURE produces a mean population
estimate at 32 rhinos with Standard Error
4.2381, while calculation using Lincoln-
Peterson formula produces a mean estimation
of 41 rhinos with standard error 19.07. The
smallest standard error is produced from the
use of CAPTURE software, which suggests
a modest uncertainity in the population
estimate compared to the Lincoln-Peterson formula.
Based on the above calculations, and manual
identication from rhino photos, it can be concluded
that with a 95% degree of condence that the rhino
population on the peninsula of Ujung Kulon NP
during the period of April 2008 to September 2009
was between 29 and 47 rhinos. Closure test suggests
that the closure assumption is violated. This may
be true due to the births and mortalities of rhinos
throughout the survey period causing the demographic
closure to be violated; however, the geographic
closure is met during the surveys. Furthermore,
violation to the closure assumption is common when
a survey is carried out over a long period of time
where there is also a possibility of time dependent
wallowing behaviour due to the reduction of wallow
holes in the dry season.
In comparing the identication results on the
age structure between 2004 and 2009 it is clear that
although the sex ratios do not differ between the two
periods, the age structures do differ. The differences
in age structure may be attributed to the growth of
2004’s subadult individuals into adult individuals in
2010, thus indicating a shift towards an adult-biased
population. However, the increase in the percentage of
calves indicates that this population is still capable of
producing offspring, although almost all of the 2009
newborns are males, which pushed the sex ratio to
male-dominated.
Descriptive analysis in comparing the birth
and mortality rates from 2000 to 2010 shows a net
population growth of ve rhinos within the 10-year
period (0.5 net growth per year or approximately
Figure 7. Comparison of average birth and mortality
of Javan rhino from 2000 through 2010.
Estimating Javan rhino population in Ujung Kulon National Park

98 Pachyderm No. 49 January–June 2011
1% population growth). Although not signicant,
and still much lower than the targeted 3% annual
population growth (PHKA, 2007), the population
might potentially be growing. However, the mortality
recorded in 2010 (three deaths) is relatively higher
than average, so further investigation on the cause of
death in 2010 is necessary. Since poaching has been
stopped, other causes of death of adult rhinos will
need to be carefully examined. The possibility of
disease must not be overlooked. This should enable
population managers to prevent an increase of the
mortality rate within these populations in the future.
In addition to studying the cause of mortality, such
as diseases and other abnormalities, the stagnant
population for the past 10 years suggests that the
carrying capacity of the Ujung Kulon peninsula
may have been reached. Therefore, future efforts to
save the Javan rhino must include: improving the
existing habitat quality (increasing food plant quality
and abundance), locating sites outside the current
geographical distribution to be designated as a second
habitat, and the translocation of individual rhinos to
the second habitat to start a new population. Having
another population of Javan rhinos outside their
current distribution in Ujung Kulon NP will greatly
increase the chance of survival of this species.
Conclusions
Implementation of camera/video trap surveys ap-
pear to be a good method for monitoring Javan rhino
population in Ujung Kulon NP, as it enables identica-
tion of individual rhinos. Accurate identication is a
prerequisite in using mark-recapture analysis, as the
identication serves marking of individual specimens.
Judging from the standard error produced from using
CAPTURE program and Lincoln-Peterson estimation
for mark-recapture it can be concluded that the former
yields lower uncertainity in the estimation, as it pro-
duces a much smaller standard error than the latter.
Based on this long-term study to monitor the popula-
tion of Javan rhinos (Rhinoceros sondaicus) in Ujung
Kulon NP, the rhino population size is estimated at
a minimum of 29 and a maximum of 47 individuals.
Despite the male-biased sex ratio the population is
capable of reproduction, but due to the the mortality
rate the net population growth is only 0.5 individual
per year (which corresponds to 1% population growth
per year between the years 2000 and 2010). In order
to achieve the target of 3% net growth of the Javan
rhino population, the birth rate needs to increase and,
importantly, the mortality rate needs to be reduced.
Acknowledgements
The research is made possible in co-operation with
Ujung Kulon NP Authority, Indonesian Ministry
of Forestry, WWF, International Rhino Foundation
(IRF), Asian Rhino Project (ARP), and WWF-AREAS
(Asian Rhino and Elephant Action Strategy). Also
thanks to Abishek, Stephan Wulfraat and Arnaud Lyet
for the valuable input on the statistical and editorial
aspects of mark-recapture estimation.
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