Population size estimates and distribution of the African elephant using the dung surveys method in Rubondo Island National Park, Tanzania

Abstract

A study to estimate population size and distribution of elephants in the Rubondo Island National Park
(RINP) was conducted between March and July 2014. It involved elephant dung survey methods. In
estimating elephant dung pile density, a total of 217 dung piles were enumerated in 58 transects (each 1
km). The on-site dung decay rate computed from 100 marked fresh dung piles was estimated to be
0.01542 per day. By combining estimated dung pile density, on-site decay rate and defecation rate of 17
dung piles per day, the study found an estimate of about 102 elephants (95% CI, 72-144). Furthermore,
results of this study indicate that, elephants were found to be more concentrated on the central and
northern zones, which are the areas of the park that have some open glades allowing elephant to
access the area easily to lake shores. The information generated from the study can be incorporated
into setting up future management strategies for elephant conservation in RINP.
Key words: Rubondo Island National Park (RINP), distance sampling, dung pile density, decay rate.

Full text

Vol. 8(6), pp. 113-119, June 2016
DOI: 10.5897/IJBC2015.0873
Article Number: 2418F7658739
ISSN 2141-243X
Copyright © 2016
Author(s) retain the copyright of this article
http://www.academicjournals.org/IJBC
International Journal of Biodiversity
and Conservation
Full Length Research Paper
Population size estimates and distribution of the
African elephant using the dung surveys method in
Rubondo Island National Park, Tanzania
Simon Mwambola1*, Jasper Ijumba2, Wickson Kibasa3, Emmanuel Masenga4, Ernest Eblate4
and Linus Munishi1
1School of Life Sciences and Bio-engineering, Nelson Mandela African Institution of Science and Technology, P. O. Box
447, Arusha, Tanzania.
2School of Material, Energy, Water and Environmental Sciences, Nelson Mandela African Institution of Science and
Technology, P. O. Box 447, Arusha, Tanzania.
3Tanzania National Parks, Rubondo Island National Park, P. O. Box 3134, Arusha, Tanzania.
4Tanzania Wildlife Research Institute, P. O. Box 661, Arusha, Tanzania.
Received 8 July, 2015; Accepted 7 October, 2015
A study to estimate population size and distribution of elephants in the Rubondo Island National Park
(RINP) was conducted between March and July 2014. It involved elephant dung survey methods. In
estimating elephant dung pile density, a total of 217 dung piles were enumerated in 58 transects (each 1
km). The on-site dung decay rate computed from 100 marked fresh dung piles was estimated to be
0.01542 per day. By combining estimated dung pile density, on-site decay rate and defecation rate of 17
dung piles per day, the study found an estimate of about 102 elephants (95% CI, 72-144). Furthermore,
results of this study indicate that, elephants were found to be more concentrated on the central and
northern zones, which are the areas of the park that have some open glades allowing elephant to
access the area easily to lake shores. The information generated from the study can be incorporated
into setting up future management strategies for elephant conservation in RINP.
Key words: Rubondo Island National Park (RINP), distance sampling, dung pile density, decay rate.
INTRODUCTION
The African elephant (Loxodonta africana) is the largest
terrestrial mammal and an icon of the African wilderness,
the population of which is declining across its range
(Blanc, 2008). The species is known to exist in a variety
of habitats ranging from tropical forests, savannah to
deserts and the species tends to extend habitats in
searching for food, water and cover (Blanc, 2008
Stephenson, 2007). Some findings have shown that
elephants need large home ranges and require extensive
areas to meet their basic metabolic requirements
*Corresponding author. E-mail: simonmwambo@gmail.com. Tel: +255-716-035980.
Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution
License 4.0 International License

114 Int. J. Biodivers. Conserv.
(Shannon et al., 2008).
The elephant populations are declining in most
protected areas across the region due to poaching and
habitat loss (Blanc, 2008). In 2007, it was estimated that
elephant numbers on the African continent were between
472,269 and 689,671 (Blanc et al., 2007). Currently, it is
estimated that the African elephant population ranges
between 419,000 and 650,000 individuals, and these are
predominantly found in Southern and Eastern Africa
(IUCN/AfESG, 2013). Blanc et al; (2007) estimated that
39% of the African elephant’s range is found in Southern
Africa, 29% in Central Africa, 26% in Eastern Africa and
only 5% in West Africa (UNEP/CITES/IUCN/TRAFFIC,
2013). Population estimates of large herbivores can aid
management decisions if estimates are accurate and
precise. Therefore, survey intensities should be done in a
way that could yield accurate and precise population
estimates and detect population changes for several
African elephant populations. Based on ground and aerial
censuses the elephant population in Tanzania was
estimated to be about 109,051 individuals (TAWIRI,
2009). In 2013, it was reported that, there were only
about 13,084 (± 1,816 SE) elephants in the Selous -
Mikumi ecosystem and these estimates are stated to be
the lowest records since the time when census began in
1976 (TAWIRI, 2013). By 2014, there were about 43,521
(± 3,078 SE) elephants in Tanzania (TAWIRI, 2015).
Hence, there is a decline by 60% from 109,051 (± 5,899
SE) elephants in 2009 (TAWIRI, 2015).
Since introduction of six immature elephants (two
males and four females) between 1972 and 1973
(TANAPA, 2003), the park management has been lacking
reliable updated information on population size of the
elephants and their interaction with various habitats in
RINP. It is impractical to use the direct count surveys in
estimating abundance of elephants in forest areas. The
dung count method was employed in estimating the
population of the elephants in RINP, as it is
recommended for areas where the observer(s) cannot
openly and clearly see the animals in the study area
(Barnes, 2001).
The dung count technique provides precise estimates
that could be comparable to both direct counts and aerial
surveys (Barnes, 2001, 2002). The combination of dung
pile density, defecation and decay rate of dung piles is
used for estimating population sizes of animals in forest
areas (Barnes and Jensen, 1987). Dung count surveys
provide good estimates with reasonable confidence limits
(Barnes, 2002; Eggert et al., 2003). The minimum
samples suggested for indirect surveys in the field ranges
between 60 and 80 (Varma et al., 2012). For example,
the dung count method was used to estimate the
population size of 124 elephants (95% CI, 44-242) in
Sapo National Park, Liberia with an estimated area of
630 km2 (Yaw and Sani, 2009). Following RINP to have
closed vegetation, may impose difficulty for aerial and
ground surveys. The dung count method is suitable for
providing information for long-term management of
elephant population and habitats on the Island.
MATERIALS AND METHODS
Study area description
The study was carried out in RINP, in the south-western portion of
Lake Victoria that lies 2° 18′ S and 31° 50′ E (Figure 1). Rubondo
Island National Park was gazetted in 1977 and became the tenth
National Park in Tanzania (TANAPA, 2003). The park covers a total
area of 456.8 km2, of which half (236.8 km2) is dry land (TANAPA,
2003). The altitude of the park ranges from 1,100 to 1,500 m. It
receives bimodal rainfall with long rains occurring from March to
May, short rains from October and December and a dry season of
January-February (TANAPA, 2003). Temperature is moderate
ranging from 16 to 26°C (TANAPA, 2003).
Vegetation consists of mixed evergreen and semi-deciduous
forest with common species including Croton sylvaticus, Drypetes
gerrardii and Lecaniodiscus fraxinifolius. The island consists of a
dense understory of lianas, or woody vines (Moscovice et al.,
2007). Common native fauna include the vervet monkeys
(Cercopithecus aethiops), sitatunga (Tragelaphus spekei) and
bushbuck (Tragelaphus scriptus). Several mammals were
introduced on the island including black rhino (Biceros bircornis),
chimpanzees (Pan troglodytes), giraffes (Giraffa camelopardalis),
black and white colobus monkeys (Colobus abyssinnicus) and Suni
antelopes (Neotragus moschatus) (TANAPA, 2003). Black rhino
has become extinct on the island during the wave of poaching in
East African countries including Tanzania in 1980s (TANAPA,
2003).
Study design and data collection
Elephant dung pile-decay rate
The decay rate study was designed based on the information of
sites reported to have frequent elephant visits. In addition, some
fresh dung piles that were encountered during survey of dung
density were included in the dung decay study. Due to limitation of
time and financial resources, the prospective method was
employed. Through this method, fresh dung piles were marked and
monitored at specific time intervals until their disappearance.
Searches and monitoring of marked fresh dung piles took about
three (3) months. Following the methods established by Alfred et al.
(2010), elephant dung piles were classified as fresh meaning less
or equal to 24 hours post-defecation based on the presence of flies,
odour and moisture. Fresh dung piles were marked with wooden
rods and tagged with pieces of printed tape of 1 m in length.
Monitoring of decay rate was done after every five to seven days for
a period of three months. The dung disappearance score was
assessed during the monitoring time period based on the
categories of classification as established by (Barnes, 2002; Alfred
et al., 2010).
Other parameters pertinent to dung decay rate including
presence of flies, dung beetles, vegetation type, canopy cover,
altitude, local name of the site and weather were also noted. The
location of dung piles was marked by GPS to aid monitoring and
estimation of dung disappearance rate. Other tools used during
data collection included, measuring tape, digital camera, field knife
and folder file.

Mwambola et al. 115
Figure 1. Map of Tanzania (inset) showing the study location of RINP.
Dung pile density
The standard line transect method was used in estimating elephant
dung pile density (Buckland et al., 2001). Surveys for enumerating
number of dung piles on the island along the designed line
transects took three months. Prior to data collection line transects
were systematically distributed on a map of RINP with a fixed length
of 1 km and at intervals of 1 km apart (Figure 1). Transects were all
designed to run in a south to north direction. Estimation of density
of elephant dung piles was based on three major assumptions;
dung piles within each transect could be detected with certainty,
dung piles were detectable at their initial location and
measurements of perpendicular distances were exact (Buckland et
al., 2001). The tape measure was used to work out perpendicular
distances from transects to the centre of the dung piles
encountered.
Classification of dung piles for enumeration used in estimation of
dung pile density was based on criteria (S1-S5) developed by
Alfred et al. (2010). A total of 58 transects were used for dung
survey in determining elephant density and distribution in RINP. To
obtain comprehensive information on dung counts, surveys were
conducted between 9 am and 4 pm every day to minimize the effect
of canopy cover on detecting dung piles along the line transects. A
team consisting of three personnel (one researcher, one field
assistant and one armed park ranger) walked along transects.
Distribution of elephants in RINP
Elephant dung piles encountered through transect surveys were
recorded as indicators of distribution. Other indicators of distribution
such as elephant trails, wallowing sites, live elephants, foraging
signs, carcasses and foot prints were also noted.
Data analysis
Elephant decay rate and dung piles density
The statistical programme GENSTAT was used in calculation of the
mean survival time of dung piles (Meredith, 2007). Elephant dung
pile decay rate was obtained by finding the mean survival time of all
decayed samples and then the reciprocal value obtained was
considered to be the estimate value for decay rate per day in the
area (Buckland et al., 2001).
Computation of dung pile density was performed by using the
DISTANCE 6.0 program (Thomas et al., 2010). Five models were

116 Int. J. Biodivers. Conserv.
Table 1. Summary of results of elephant dung pile density by using five models on DISTANCE® program.
Model used
#Parameter
AIC
ESW/EDR
D
%CV
95%CI
Lower
Upper
Half normal+cosine
2
704.4
3.59
520.7
20.06
351.21
772
Half normal+simple polynomial
2
713
3.65
512.8
18.12
358.45
733.5
Uniform+cosine
2
718
3.48
537.6
17.12
382.71
755.3
Hazard rate+cosine
2
691.8
3.95
473.2
17.35
335.43
667.6
Hazard rate+Hermite polynomial
2
691.8
3.95
473.2
17.35
335.43
667.6
Explain this (AIC, ESW/EDR, D, %CV, 95%CI)
fitted to obtain precise estimate of the elephant population as
recommended in distance sampling (Table 1). There was no
difference on the outputs when truncation applied to various
models. The hazard rate model with some adjustments (Cosine and
Hermite) gave consistent results with lowest Akaike’s Criterion
Information (AIC) values. Hence, by having lower AIC value and
sound histogram, these models were considered as the best
estimators for density of elephant dung piles.
Elephant density and numbers
The dung pile density obtained by the distance programme
(Buckland et al., 2001) was converted to elephant density. Due to
limitation of time and financial resources, adopted defecation rate of
17 dung piles per day for Kibale National Park in Uganda was used
in estimating the population size of elephants (Wing and Buss,
1970). Calculation of density and number of elephants was done
according to McClanahan (1986), Barnes and Jensen (1987).
Where, E represents elephant density, D is the dung pile density
obtained from distance analysis (Buckland et al., 2001), R is the
dung decay rate and Y represents the defecation rate.
The combination of estimates of dung pile density, decay and
defecation rates was used to give an estimate of population size of
elephants in Rubondo Island National Park. The distribution of
indicators of elephants was analysed by assessing the percentage
of encounters of indicators in different habitats on the island.
RESULTS
Dung decay rate, dung piles density and elephant
population estimates
Five sites encountered with fresh dung piles were
surveyed; Maji Matakatifu (4 dung piles- woodland),
headquarters (23 dung piles-woodland), air strip (21 dung
piles-open woodland), road to Mlaga ranger post (30
dung piles-woodland) and Mlaga campsite (25 dung piles
- glade), Kamea road (1 dung piles - woodland) and
Mlaga to Lukaya/Lukukuru road (11 dung piles -
woodland). Although 115 fresh dung piles were marked
and monitored in various habitats, 100 dung piles were
used for the determination of decay rate as 15 were not
relocated. This was due to the disturbance led by road
maintenance of road from headquarters (Kageye) to
Mlaga ranger post.
Mean survival time for dung piles was 64.842 (S.E. ±
1.36) days with coefficient of variation of 2.097. The
elephant dung pile decay rate was 0.01542 per day. A
total of 217 dung piles were enumerated in a total length
of 58 km of parallel line transects. The elephant dung
piles density was estimated to be 473.22 (95% C.I.
335.43- 667.60) dung piles per km2 (Table 1). Akaike’s
Information Criterion (AIC) provides a quantitative
method for model selection and model with lowest AIC is
selected for final analysis and inferences (Buckland et al.,
1993). It attempts to identify how the model that fits with
the data well. Based on the findings of this study in
determining the dung piles density, Hazard rate with
cosine and hermite polynomial adjustments gave the
lowest AIC values (691.8) (Table 1). Effective strip width
(ESW) is the average distance where dung piles were
detected during dung count survey. The coefficient of
variation (CV) gives a measure of precision of the
estimate and is usually expressed in percentage. Outputs
having low variances are considered to be more precise.
The model which was considered to give the precise
estimate has a percentage of coefficient of variation of
17.35 (Table 1). The 95% confidence interval (CI) is used
in determining the lower and upper value of an estimate.
In DISTANCE program AIC, ESW, %CV and 95%CI are
computed automatically.
Basing on the findings of this study, RINP was
estimated to have about 102 elephants (95% CI, 72-144).
The density of elephants in the RINP was estimated to be
less than one elephant (0.43) per km2.
Distribution of elephants on the Island
About 523 of elephant signs were recorded during the
survey. Dung piles including other indicators such as
elephant trails, carcasses, live elephants, wallowing sites,
foot prints and foraging signs were also observed. It was

Mwambola et al. 117
Table 2. Summary of percentage of encounter (s) of indicators of elephant distribution in RINP.
Indicators of elephant distribution
Number of encounter(s) of
indicator
Percentage
Dung piles
343
65.58
Trails
50
9.56
Foot prints
56
10.71
Wallowing sites
18
3.44
Foraging signs
46
8.80
Live animals
8
1.53
Carcasses
2
0.38
Figure 2. Map of RINP showing distribution of dung piles as indicators of presence of elephants in various habitats.
found that 65.58% (N=343) of dung piles and 0.38%
(N=2) of carcasses as the highest and lowest encounters,
respectively (Table 2). Two carcasses of elephants were
found in the central and southern zones of the park with
tusks intact. Elephant activities were mostly observed to
be concentred on the central and northern zones of the
study areas (Figure 2). Frequent visits of elephants have
been reported to ranger posts associated with feeding
activities. Most encountered plant species browsed by
elephants included Annona senegalensis, Phoenix
reclinata, Ekerbegia capensis and Aeschynomene
elaphroxylon.
DISCUSSION
Elephant dung pile decay rate
The study of elephant dung pile decay rate as a means of
estimating abundance of elephants was the first to be
conducted in RINP. A precise estimate of decay rate in
the study area was considered to yield precise estimates

118 Int. J. Biodivers. Conserv.
of elephant numbers in forest areas. Dung piles,
deposited in areas with high vegetation canopy cover
were observed to decay faster compared to those
underlow or no canopy cover. This may be due to the
steady environmental temperatures which favour a higher
rate of dung decomposition. Deposition of dung piles in
habitats without canopy cover exposes microorganisms
(dung beetles, termites and microbes) to unfavourable
conditions for decomposition to take place. The climate
variables (rainfall, irradiance and temperature) and
elephant diet are also considered as the determinant of
elephant dung piles decay rate (Barnes, 2001).
Moreover, the nature of food materials of plant species
eaten by elephants has great influence on disappearance
of deposited dung piles.
Elephant density and population estimate
Results from this study show that, there has been an
increase in the number of elephants from six (6) in 1973
to 102 elephants in 2014, implying that the RINP
elephant population is increasing. Forage biomass,
forage quality, water availability, shade and plant species
composition has correlation with density and distribution
of elephants (Harris et al., 2008). Increase in elephant
population in RINP may be contributed by receipt of
enough rainfall annually, presence of water body
surrounding the island, high canopy covers. Availability of
shades almost over the island makes RINP as the
suitable habitat for elephants in regulating metabolism of
these large herbivores.
These findings are indicative of the fact that, elephant
population growth on Rubondo Island is promising.
Based on the physiognomy, paved paths and resources
utilized by elephants on the island, findings of this study
suggest that the island is able to support the existence of
wildlife species. However, due to limited size of the island
with only dry land of 236.8 km2, large number of
elephants may exceed the carrying capacity of the area
probably in the future. As a result, the ecosystem on the
island may lose its aesthetic value due to overexploitation
of resources by elephants. Until the time of the survey,
only three elephant carcasses with tusks had been
reported in all three incidents, it is possible that the
deaths were caused by natural factors. There has been
no field report of elephant poaching on Rubondo Island.
The detection probability during transect survey in
enumerating number of dung piles was affected by a
number of factors, including composition of understory
since the nature of vegetation in RINP is vast rain forest
type. Cloudy weather and canopy cover also influenced
poor performance of GPS and the ability to detect dung
piles during transects surveys. Traditionally, steep terrain
and dense woods pose some hindrances in accessing
some areas, which was also the case during the current
survey in the southern part of the park.
Distribution
High density of dung piles was found at the central and
northern parts of the park indicating presence of more
elephants in these areas (Figure 2). Some studies have
shown that, resources availability and accessibility
influence the elephant activities (Shannon et al., 2008).
Raphia swamps were found to have high level of
elephant activities in Sapo National Park in Liberia (Yaw
and Sani, 2009). In fact, suitable habitats are preferred by
elephants. Presence of good road network and tracks at
the central and northern zones enhance easy movement
of humans and animals near or along the tracks.
Occurrence of elephants in small herds encourages
flexible movement between different habitats. High
density of dung piles was also encountered close to the
lake shore, revealing that availability of water predicts
movement and activities of elephants in RINP. During
periods of shedding leaves by trees, elephants were
observed to prefer utilizing habitats along the lake. In
some circumstances elephants were observed browsing
on Aeschynomene elaphroxylon, which is found in water
near the lake shore. In some other instances, elephant
signs were encountered in habitats where lemon trees
are found. Remains of lemon fruit were observed among
contents of some elephant dung piles. Phoenix reclinata
is mostly utilized by elephants because it can easily be
uprooted and eaten. Foot prints, trails, carcasses,
wallowing sites and elephants themselves were regarded
as other signs indicative of presence of the mega
herbivores and their related activities in various habitats.
Conclusion
Findings of this study have shown that, the elephant
population in RINP is increasing. This remark may be due
to low level of poaching and successful adaptation of
elephants to environments in forest areas on the island.
High concentration of dung piles at the central and
northern zones of the park may imply the availability of
suitable habitats for elephants. It is recommended that,
park management should continue to monitor population
trend of the elephant on the island in specific interval of
time. Moreover, further studies are needed to determine
the carrying capacity of the island. This may be helpful in
controlling the number of elephants so that cannot disrupt
the welfare of other wildlife species on the island. In
context of contemporary management of endangered
wildlife species, in future there is a need to undertake
genetic studies to undertake the inbreeding risks of
isolated small population on the island.

Conflict of Interests
The authors have not declared any conflict of interests.
ACKNOWLEDGEMENTS
We thank the Government of United Republic of
Tanzania through the Commission for Science and
Technology (COSTECH) and The Nelson Mandela
African Institution of Science and Technology for funding
this research. We acknowledge Professors Stephen
Buckland and Len Thomas for their technical assistance
and training on survey design and data analysis for
estimation of population size of elephants in forests.
Mwita Machoke and Laurent Nzuki assisted on design
GIS-base map for line transects survey and analysis. We
thank the Tanzania Wildlife Research Institute and
Tanzania National Parks for granting permission to
conduct research in Rubondo Island National Park. We
thank Sam Ramadhani, Jeremiah Johansen and all park
rangers in RINP for their assistance and protection during
data collection.
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