Population Structure, Composition and Abundance of Elephants Elephas Maximus in Minneriya National Park, Sri Lanka

14 Pages·2003·8.6 MB·

by  Charles Santiapillai

POPULATION STRUCTURE, COMPOSITION AND ABUNDANCE
OF ELEPHANTS ELEPHASMAXIMUS IN MINNERIYA NATIONAL PARK, SRI LANKA
With six text-figures and oneplate)
(
Charles Santiapillai1’2 S. Wijeyamohan3
, ,
Chaminda Wijesundara1 and Rajnish Vandercone1
Key words: elephant, Elephas maximus MinneriyaNational Park, Sri Lanka
,
The Minneriya National Park was established mainly to enhance the long-term survival of the
Asian elephant (Elephas maximus) in a predominantly agricultural area in Sri Lanka. The ancient
reservoir, after which the Park is named, is seasonally hoi^e to large numbers ofelephants because
ofthe availability ofwater and the extensive areas ofgrassland created by fluctuations in the water
level. In a preliminary study carried out from September 2000 to August 2001, a total of 974
A
elephants were recorded, ofwhich 797 were classified according to age and sex. quarter ofthe
observations referred to solitary males. The most frequently observed grouping comprised 5-10
individuals that represent the family unit. The population structure appears to be equally divided
between the adults and the other categories. The observed mean adult malerfemale sex ratio was
1:2.9, closeto thenational average of1 :3. Largegroupingsofelephantwere observed when thedrop
in water level in the reservoir resulted in increase in the area ofthe grazing grounds. The largest
group observed comprised 70 animals. There were also all-male groups, whose composition varied
from 2-6. Most ofthe animals were observed emerging from the forest to feed on the grasslands
between 1600-1700 hrs in the evening. During the rainy season, as the water level in the reservoir
increased, floodingthe grazinggrounds, elephants moved to areas outsidethe Park, causingconflict
with the farming community. The gradual build up ofelephants in the Park leadingto the observed
maximum of319 animals, translates into a crude densityof3.6 animals persq. km, which is among
the highest densities recorded in Asia. Therefore Minneriya National Park represents one ofthe
important areas forelephant conservation in Sri Lanka. Butthe survival ofthe elephant outsidethe
protected area can only be assured if appropriate measures are adopted to reduce the human-
elephant conflict.
Introduction population growth and deteriorating fertility of
the land has led to increased encroachment and
Despite its small size, the islandofSri Lanka degradation of forests inhabited by the elephant
(65,610 sq. km) supports several viable and other wildlife. This has led to a build up of
populations of elephants estimated to number elephantnumbers withinthe protectedareas, while
between 3,000 and4,000 animals (Santiapillai and outside elephants are finding it increasingly
Jackson 1990). To conservethe elephant and other difficult to move about and adjust their densities
wildlife, Sri Lanka has set aside about 12.5% of to seasonal changes in vegetation and water
the land area underprotection. Outside the system availability across their range. One of the more
ofprotected areas, a combination ofhigh human recent additions to the system ofprotected areas
is the MinneriyaNational Park, opened to visitors
'Department of Zoology, University of Peradeniya, Sri on May 29, 1998. It is known to support high
Lanka. elephant numbers seasonally in response to
2Email: [email protected]
changes inthe wateravailability and grazingareas.
•Department of Biology, Faculty of Applied Science,
Vavuniya Campus of the University of Jaffna, Vavuniya, However, given its central location in a
Sri Lanka. predominantly agricultural area, conflict between
308 JOURNAL BOMBAY NATURAL HISTORY SOCIETY, 100(2&3), AUG.-DEC. 2003
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POPULATION OF ELEPHANTS IN MINNERIYA NATIONAL PARK, SRI LANKA
man and elephant has become inevitable. No unicolor barking deer Muntiacus muntjak wild
, ,
studies have so far been carried out on the pigSusscrofa andjackal Canis aureus. Both sloth
ecology of the elephant in Minneriya National bear Melursus ursinus and wild buffalo Bubalus
Park to document the seasonal build up of its bubalis are very rare in the Park, but domestic
numbers. It was to address these issues that a cattle range freely in large numbers.
preliminary study was carried out from September The Park is also renowned for its rich and
2000 to August 2001. diverse waterfowl, both indigenous as well as
migrant. Resident birds include the painted stork
Study Area Mycteria leucocepha/a), Asian openbill-stork
(
(Anastomus oscilans), white-necked stork
The 8,889 ha Minneriya-Giritale Nature (Ciconia episcopus), and the lesser adjutant-stork
Reserve was established on February 12, 1988, (Leptoptilos javanicus). The reservoir itself
and was subsequently upgraded to a National supports a variety of economically important
Park on August 12, 1997. It is situated next to the fishes such as Labeo dussumieri, Puntiussarana,
Minneriya-Giritale Sanctuary (6,693 ha), a part of P. dorsalis P. chola, Cyprinus carpio,
,
which was designated as a national biosphere Mastacembe/us armatus Ophicephalus striatus
, ,
reserve (809 ha). The entire Minneriya-Giritale etc. (IUCN 1990). The annual rainfall forthe year
complex is situated in an important agricultural 2000 was 1 ,344 mm, and the principal rainy season
area in the Polonnaruwa district in the North extended from October to January. During the
Central Province ofSri Lanka (Fig. 1 ). The Park is dry season, which lasts from February to
named after the ancient irrigation reservoir September, the Park receives very little rainfall,
Minneriya, built by King Mahasena in the 3rd and none at all in May, June and July. The average
century AD. It has a capacity of 2,250 ha when annual temperature is 27.2 °C.
full and a catchment area of24,000 ha. The main
source ofwater is from a diversion ofthe Amban Methods
Ganga, along the Elahara Channel (IUCN 990).
1
Grasslands and a belt ofdry mixed evergreen All observations on elephants in Minneriya
forest surround the reservoir. The vegetation in were made from a vehicle. We adopted the road-
the grasslands bordering the reservoir consists strip count method ofHirst 969) to monitor the
(1
ofspecies such as Cynodon dactylon Brachiaria fluctuations in elephant numbers. The study area
,
mutica Echinochloa colonum Paspalum was visited at monthly intervals during which
, ,
vaginatum and Digitaria longiflora many of observations on elephants were made along a 14
,
which are truly hydrophytic. In addition, extensive km stretch ofmotorable foresttrack, through forest
patches of grasslands composed mainly of and grassland habitats. Although some animals
Imperata cylindrica (Illuk) and Panicum were observed up to a maximum distance of300
maximum (Pohon) are also common. The forest is m, most ofthe observations fell within 200 m. As
dense with species such as Drypetes sepiaria the elephants in Minneriya have been known to
,
Chloroxylon swietenia ViIex altissima emerge from the forest predominantly during the
, ,
Manilkara hexandra Limonia acidissima evenings, all sightings of elephants were made
, ,
Diospyros ovalifolia and Berrya cordifo/ia. The between 1500 and 1900 hrs. At every sighting,
fauna includes not only the endangered species, the location of the elephants, their number,
the Asian elephant Elephas maximus and the composition and activity were noted. For census
leopard Pantherapardus but also othermammals purposes, the four categories recognised by
, —
such as spotted deer Axis axis, sambar Cervus Eisenberg and Lockhart (1 972) namely adult,
JOURNAL BOMBAY NATUML HISTORY SOCIETY I00(2&3), AUG.-DEC. 2003 309
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POPULATION OF ELEPHANTS IN MINNERIYA NATIONAL PARK SRI LANKA
,
Fig. 1 : Map ofMinneriya National Park, Sri Lanka, showing the reservoir (shaded area),
grazing grounds (open area) and forest (cross-hatched area)
—
A
subadult, juvenile and calf were adopted. individuals (adult or subadult males), and 10 (or
group ofelephants refers to morethan two animals 10.6%) referred to all-male groups, whose size
A
ofany age or sex movingtogether in a coordinated ranged from 2-6 animals. total of5 1 family units
manner, while a family unit or herd refers to an were identified (Table ofwhich 25 (or49%) had
1),
integrated unit ofclosely related elephants ofall no adult bulls, while 8 (15.7%) had only one bull,
classes excluding adult males (Laws 1970). 9 (17.6%) had two bulls, 4 (7.8%) hadthree bulls,
3 (5.9%) had four bulls, and 2 (3.9%) had eight
Results and Discussion bulls (Fig. 2). The association ofbulls with family
units was temporary and was related to the
Population Structure presence of oestrus females (Short 1966). In an
Between September2000 and August 200 extraordinary instance, there were 8 bulls
1
a total of 974 elephants were sighted from 94 associated with just two cows. Observations by
observations ofwhich 797 animals were classified Douglas-Hamilton (1972), Croze (1974), Laws et
according to age and sex. Nine ofthe observations al. (1975) and Poole and Moss (1981) have largely
could notbe classified. Ofthe 94 observations on dismissed thetraditional view ofa single bull being
elephants, 24 (or 25.5%) represented solitary an integral part ofa family unit to the exclusion of
310 JOURNAL BOMBAY NATURAL HISTORY SOCIETY, 100(2&3), AUG.-DEC. 2003
POPULATION OF ELEPHANTS IN MINNERIYA NATIONAL PARK SRI LANKA
,
Table 1: The composition of the family units of elephants in Minneriya National Park
Family unit Adult males Adult females Subadults Juveniles Calves Total
1 _ 11 8 5 4 28
2 - 1 1 1 - 3
3 - 2 1 1 - 4
4 - 3 3 3 1 10
5 - 2 - - 1 3
6 2 14 21 6 6 49
7 - 3 - 2 1 ? 6
8 - 5 2 - 4 11
9 - 3 - 1 - 4
10 - 1 1 - 1 3
11 - 2 - 2 - 4
12 - 2 - - 2 4
13 2 17 12 10 4 45
,
14 A 10 6 3 4 24
1
15 - 1 2 - 1 4
16 2 5 1 2 10
17 - 4 - 1 2 7
18 - 2 1 1 2 6
19 6 5 2 2 16
1
20 - 6 4 2 3 15
21 - 10 9 3 1 23
22 1 2 4 2 1 10
23 - 5 4 2 - 11
24 - 22 7 4 3 36
25 - 11 3 3 4 21
26 2 5 2 4 - 13
27 - 1 - 2 - 3
28 2 8 3 2 2 17
29 8 9 2 3 23
1
30 2 29 18 15 6 70
31 1 12 6 6 4 29
32 2 13 4 3 3 25
33 4 2 2 2 2 12
34 - 2 2 1 - 5
35 - 3 - 1 3 7
36 1 7 1 2 2 13
37 - 1 5 1 - 7
38 - ;?5 4 2 1 12
39 3 1 2 - - 6
40 8 21 10 6 4 49
41 4 2 1 3 - 10
42 1 2 - 1 1 5
43 8 1 1 - - 10
\
44 3 7 3 - 1 14
A
45 7 - 4 5 20
46 i3 .>.1 - 1 - 5
47 4- 1 2 - 1 4
48 2 4 4 2 1 13
49 1 1 1 1 - 4
50 3 1 2 2 - 8
51 2 1 2 - 1 6
Total 66 296 179 119 87 747
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POPULATION OF ELEPHANTS IN MINNERIYA NATIONAL PARK, SRI LANKA
Bulls per herd (n= 51)
60
i
Number of bulls per herd
Fig. 2: The proportion ofadult bulls in family units or herds observed in Minneriya National Park
otheradultbulls (Rushby 1965, Sikes 1971, Poche (or23.8%)were subadults and206 (or25.8%) were
1974). Nevertheless, as Barnes (1982) points out, young animals (bothjuveniles and calves). Such
in situations where elephants form very large an adult-dominated age structure is characteristic
groups, it may pay for a bull elephant to exclude ofseveral populations ofelephants in Sri Lanka
other bulls and remain with a group, given the (Eisenberg and Lockhart 1972, McKay 1973,
opportunities available for mating with different Nettasinghe 1973, Ishwaran 1981, Santiapillai et
females thatcome into oestrus. In such a situation, al. 1984, Katugaha et al 1999). An age ratio of
there is no need for the bull to move out in search this type is to be expected in a species
ofcows in heat. But in Minneriya National Park,
Population structure (n = 797)
given the small size ofthe groups, there would be
no real advantage for a bull to be permanently
associated with a group. In such a situation, the
best strategy for a bull to enhance reproductive
success would be to move from group to group in
search of cows in oestrus. Monthly changes in
structure and composition of the population of
elephants are given in Table 2. As can be seen
from Fig. 3, the population structure ofelephants
in Minneriya appears to be equally divided
between adults and the other categories put adults subadults young
Age classes
together. Of the total 797 animals that were
Fig. 3: The proportion ofadults, subadults and young
classified, 401 (or 50.3%) were adults (males,
observed in the population ofelephants
including solitary bulls, and females), while 190
in Minneriya National Park
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POPULATION OF ELEPHANTS IN MINNERIYA NATIONAL PARK, SRI LANKA
Table 2: Monthly changes in population structure and composition of elephants in Minneriya National Park
Date Adult Adult Sub- Juveniles Calves No. calves/ Total (Unclassified)
2000-01 males females adults 100 cows
September 10 76 58 34 28 36.8 206 (44)
October 16 80 45 28 19 23.8 188 (131)
November 9 70 40 28 18 25.7 165 -
December 0 0 0 0 0 0.0 0 -
January 4 2 2 2 2 100.0 12 -
February 0 0 0 0 0 0.0 0 -
March 3 0 0 0 0 0.0 3 -
April 1 0 0 0 0 0.0 1 (2)
May 3 0 1 0 0 0.0 4 -
June 7 5 3 2 3 60.0 20 -
July 2 8 6 3 2 25.0 21 -
August 48 57 35 22 15 26.3 177 -
Total 103 298 190 119 87 797 (177)
characterised by exceptional longevity, long populations. The observed mean adult
gestation period and extended inter-calving male:female sex ratio in Minneriya, i.e. 1 :2.9, is in
intervals. keeping with the national average of 1:3
determined by McKay (1973), Kurt (1974) and
Sex-ratio Hendavitharana etal. (1994). However, within the
Among Asian elephants, the sex ratio does family units, the ratio becomes slightly more
not appearto shift significantly from the expected biased in favour ofthe females 1 :4.5 (Table 1), as
1:1 ratio until the subadult stage is reached several of them were not associated with bulls.
(Sukumar 1989). The elephant being a The adult sex ratio is significantly biased in favour
polygynous, sexually dimorphic species, the adult ofthe females in the months ofSeptember, October
sex ratio is unlikely to be in parity but varies andNovember, duringwhich the ratio ranged from
considerably from place to place (McKay 1973), 1:5 to 1:7.7 (Table2). However, as Sukumar(1989)
and is usually biased in favour of the females points out, since at any time, a proportion ofthe
owing to a higher natural mortality in the males. cows would be either pregnant or in lactation
As Sukumar (1989) points out, the sex ratio at anoestrus, not all the adult females would be
stable age distribution will depend on the available for mating with the bulls. Hence, the
magnitude ofthe difference in mortality rates of operational adultsex ratio would notbe as skewed
male and female elephants, assuming an equal as the one observed in the population. The
ratio at birth. Furthermore, the difference in the observed adult sex ratios seem to indicate that
adult sex ratios in an area could be due to either a the elephant population is not subject to very
high mortality amongmales orthrough dispersion high mortality as a result of either poaching or
ofthe animals in space and time (McKay 1973). conflict with man. Given the fact that females do
Thus, as Katugaha et al. (1 999) point out, even not carry tusks and only a small proportion ofthe
under normal conditions, the sex ratios of bulls (less than 7%) are tuskers in Sri Lanka,
progressive age classes would become poaching for ivory is not the major cause for the
increasingly female-biased in elephant disparate sex ratio. In Minneriya, there were only
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POPULATION OF ELEPHANTS IN MINNERIYA NATIONAL PARK, SRI LANKA
4 tuskers: 2 juveniles and 2 adults. Both adults around the Minneriya reservoir. The largest
were single tusked, one being right tusked and grouping consisted of70 individuals. In addition,
the other left tusked, and so could easily be there were ten all male groups. These groupings
identified. appear to be temporary associations between
sexually mature elephants held together by weak
Group size social bonds. They exhibit short-term cohesion.
The most frequently observed grouping Such all male groups with rapidly shifting
comprised 5-10 individuals that represented the composition of individuals have also been
family units or herds (Fig. 4). A number offamily recorded in Africa (Croze 1974). The maximum
units associate temporarily to form the larger number of bulls seen together in Minneriya was
groupings seen in the Park. Family units vary in six (range 2-6).
size from two (mother-calf units) to nine (three The composition ofone ofthe groups (No.
adult females with their offspring). The mean 43 in Table 1) that were observed in Minneriya
group size including solitary individuals is 1 0.4. If National Parkwas rather strange. Ithad eight bulls
solitary individuals (i.e. bulls) are not taken into and two cows. According to Dr. Phil Kahl (pers.
account, then the average group size increases to comm.), who had studied the phenomenon of
13.6 (range 2-70). Of the 51 groups numbering musth in African elephants, a possible explanation
more than three individuals, 25 (or 49%) had no for such a strange grouping is that the older of
adult bulls. The association of adult bulls with the females was a cow in oestrus; the younger
family units was common in the months from female, probably a previous calfofhers that was
August to November. Large groups of elephants staying on with the mother. The 8 bulls were
were observed following the build up ofnumbers probably “suitors” hoping to mate with the adult
Group sizes (n = 974)
30
25
20
0
o
c
0
l—
§ 15
o
o
£
10
5
0
Group size
Fig. 4: Group size frequency diagram for elephants in Minneriya National Park
314 JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, 100(2&3), AUG.-DEC. 2003
POPULATION OF ELEPHANTS IN MINNERIYA NATIONAL PARK, SRI LANKA
Santiapillai, Charles et al. Elephas maximus Plate 1
:
Fig. A: A herd ofelephants around the biggest bull in Minneriya National Park, Sri Lanka
WIJEYAMOHAN
S.
PICS:
Fig. B: An encounter between two bull elephants in Minneriya National Park, Sri Lanka
JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, 100(2&3), AUG.-DEC. 2003 315

POPULATION OF ELEPHANTS IN MINNERIYA NATIONAL PARK SRI LANKA
,
female. One of them might have been a bull in population, given that aggregations offamily units
musth, in which case he would most likely have and bull groups could be the result of stressful
been in “consort” with the oestrous female. conditions. The stress may arise through
The mean group size of elephants varies nutritional deficiency or through the loss of
over time and space, and some of the variation matriarchs following hunting (Eltringham 1977).
could be related to the availability of food The habitat diversity ofMinneriya National Park
(Leuthold 1976, Barnes 1983, Dublin 1996). In makes it unlikely that elephants may suffer from
Minneriya it appears that elephants range in small nutritional deficiency. None of the animals that
groups during the dry season when food is of were observed in the Park were in poor condition.
poor quality. Olivier (1978) correlates the decline Besides, as the Park itself is situated within an
in mean group size with a decrease in the habitat agricultural landscape, the elephants, especially
quality. It appears that smaller units ofelephants the bulls, have the opportunity to supplement
are perhaps better adapted to exploit a patchily their diet with highly nutritious food plants
distributed resource than are larger ones (White cultivated by man. Therefore, it is social factors
et al. 1993). Ofthe 33 family units having 10 or more than nutritional deficiency and loss of
more animalsthat were recorded duringthe study, matriarchs from hunting, thatmay determine group
3 (or 94%) were encountered during the rainy sizes.
1
season, and only 2 (or 6%) were seen in the dry
season. As Dublin (1996) argues, the formation Feedingactivity
of larger groups allows elephants to interact, to The distribution ofelephants in Minneriya
determine dominance hierarchies and to re- National Park appears to be aggregated, which
establish bonds. In Minneriya, there is a gradual suggests that the area is not uniformly attractive
build up of elephant numbers from August to to them. Much of the elephant feeding activity
November as animals move in from outside when was centred round the grasslands. As all the
many of the smaller water holes dry up in elephants were observed in the open grasslands
the neighbourhood. The large Minneriyareservoir between 1 500 and 1900 hrs, grazing was the most
provides a year-round supply of water. Even at important activity recorded. As Katugaha et al.
the peak of the dry season, grasslands around (1999) point out, groups of elephants usually
the reservoir become grazing areas for hundreds spend a large part of their time during the day
of elephants. The surrounding mixed evergreen within the forests, under shade, and so are not
forest provides a variety of plants on which the noticeable until they move to the grasslands in
animals browse. As the rainy season progresses, the late evenings to graze. Although elephants
the water level in the reservoir increases spend considerable time in the woodlands, trees
substantially, leading to the flooding ofthe very and shrubs make up only a small proportion of
grasslands that support large numbers of their food (Buss 1961). In Sri Lanka, grasses are
elephants in the dry season. As the water level the most important food of elephants. But
increases, the elephants disperse to other areas elephants alter their food habits in relation to
outside the Park. It is during such times that the season. Fig. 5 summarises the feeding activity
area experiences an increase in the conflict pattern of the elephants observed in Minneriya.
between man and elephant. It is also thetime when The peak of the activity was observed between
paddy plants have been planted extensively, and 1600 and 1700 hrs, when the highest number of
these provide rich feeding areas forthe dispersing elephants, 388 (39.8%)were recorded. The activity
elephants. As Laws (1974) argues, the group size fell duringthenexthour(1700-1800hrs)andpicked
is ameasure ofthe ecological health ofan elephant up once again from 1 800-1900 hrs.
JOURNAL BOMBAY NATURAL HISTORY SOCIETY, 100(2&3), AUG.-DEC. 2003 317