Does
indigestible food remains in the scats of Sloth Bear Melursus ursinus (Carnivora: Ursidae) represent
actual contribution of various diet items?
N. Baskaran1 & Ajay A. Desai 2
1,2 Bombay Natural History Society,
Elephant Project, Kargudi, The Nilgiris,
Tamil Nadu 643211, India
1 Present address: Asian Nature
Conservation Foundation, Innovation Centre, First Floor, Indian Institute of
Science, Bengaluru, Karnataka 560012, India
2 Present address: BC 84 Camp,
Belgaum, Karnataka 590001, India
Email: 1 nagarajan.baskaran@gmail.com
(corresponding author),2 ajayadesai.1@gmail.com
Abstract:The contribution of diet
items in the food of sloth bears is estimated solely based on the dry weight or
volume of indigestible food remains found in the scats, assuming that the ratio
of digestible versus indigestible matters is equal in all diet items. However, this is not true in
reality. The implication of this
assumption is that the species that contribute a larger bulk of digestible
matters are underestimated, while that of less digestible parts get overestimated
and consequently are portrayed as important food sources. This study experimentally converts the
percent contribution of important fruit items estimated using ‘indigestible
fruit remains’ in the scats into percent contribution by ‘digestible fruit
content’ using known dry weight of digestible fruit contents per volume of
indigestible items (estimated using fresh fruit samples from the field). The percent composition of various
fruit items obtained using digestible fruit content is significantly different
from that derived using indigestible fruit remains in the scats. Future studies could adopt the dry
weight of digestible matter as this method estimates the contribution of
various food items to the diet of bears more accurately.
Keywords: Indigestible and digestible food parts, scat analysis, Sloth Bear diet.
Date
of publication (online): 26 December 2010
Date
of publication (print): 26 December 2010
ISSN
0974-7907 (online) | 0974-7893 (print)
Editor: C. Srinivasulu
Manuscript
details:
Ms # o2358
Received 08
December 2009
Final received
04 October 2010
Finally
accepted 20 November 2010
Citation: Baskaran, N. &
A.A. Desai (2010). Does indigestible food remains in the scats of Sloth Bear Melursus ursinus (Carnivora: Ursidae)represent actual contribution of various diet items? Journal of Threatened Taxa 2(13): 1387-1389.
Copyright: © N. Baskaran &
Ajay A. Desai 2010. Creative Commons
Attribution 3.0 Unported License. JoTT allows unrestricted use of this article in any medium
for non-profit purposes, reproduction and distribution by providing adequate
credit to the authors and the source of publication.
Acknowledgements:We thank the Tamil Nadu Forest Department,
especially Mr. G. Kumaravelu, IFS, the then
Conservator of Forests, Wildlife Western Region, Mr. S.K. Srivasthava,
IFS, the then Wildlife Warden, Mudumalai Wildlife
Sanctuary, for permitting and funding this study. We thank Mr. J.C. Daniel, Honorary
Secretary, BNHS, and Dr. A.R. Rahmani, Director,
BNHS, for their encouragements and support during the project.
Studies on food habits of Sloth Bears Melursus ursinus mostly use
scat analysis method (Schaller 1967; Laurie & Seidensticker1977; Baskaran 1990; Gokula1991; Gokula et al. 1995; Baskaranet al. 1995; Desai et al. 1997; Joshi et al. 1997). In this method, the diet composition is arrived at from
indigested food remains in the scats using different quantitative
measures. Some studies (Schaller
1967) have used percent occurrence of various undigested food remains in the
scat, but this does not indicate the quantities consumed. On the other hand, the percent dry
weight or percent volume of indigestible food remains technique would ensure
better estimation of different food items to the diet. However, the reliability or accuracy of
this technique too largely depends on ratio of digestible versus indigestible
parts of various food items. Unfortunately, the ratio of digestible versus indigestible parts of food
items is not uniform in all food species consumed by bears. For example, Sloth Bears in southern
India consume ripe and dried fruits of Cassia fistula. The bears consume the gum-like
pulp, which exists between seeds that form less than one-third of the quantity
of the total fruit. The remaining
parts including seeds and pericarp form more than
two-thirds of the total quantum of fruit and are indigestible. Most of the studies (Laurie & Seidensticker 1977; Baskaran1990; Gokula 1991; Baskaranet al. 1995; Gokula et al. 1995; Desai et al. 1997;
Joshi et al. 1997) that adopt the percent volume or dry weight methods however
estimate the relative contribution of various food species merely based on
indigestible food remains that appear in the scat by assuming the relative
contribution of digestible and indigestible parts equally for all the
species. Therefore, species that
contribute larger bulk of digestible parts are likely to be underestimated,
while those contributing less digestible parts get overestimated, and are
consequently portrayed as important food sources of the bears. We therefore carried out an experiment
to test the accuracy of using the indigestible food remains in the scat as an
indication of relative contribution by various food species to the overall diet
of Sloth Bear. This experiment
tested only for major fruit species eaten by the bears in MudumalaiWildlife Sanctuary, Tamil Nadu, India.
Methods
Study area: This
experiment was conducted in the tropical forests of MudumalaiWildlife Sanctuary (presently redesignated as Mudumalai Tiger Reserve). The MudumalaiWildlife Sanctuary (11032’-11045’N & 76020’-76045’E),
located at the tri-junction of three southern states of India, namely Tamil
Nadu, Karnataka and Kerala, is a part of the NilgiriBiosphere Reserve. It is bounded on the north by BandipurTiger Reserve in Karnataka, on the west by WyanadWildlife Sanctuary in Kerala and on the south and east by NilgiriNorth Forest Division in Tamil Nadu. The experiment was carried out between May 1996 and April 1997 as part
of a larger study on the behavioural ecology of Sloth
Bears (Desai et al. 1997).
Evaluation
of food habits: We studied the diet composition and seasonal variation
through scat analysis as suggested by earlier studies (Laurie & Seidensticker 1977; Baskaran1990; Gokula 1991; Baskaranet al. 1995; Gokula et al. 1995; Desai et al. 1997; Joshi
et al. 1997). In the present
study, scats were collected along fixed game roads representing different
vegetation types at fortnightly intervals. Food items in the scats were segregated by analyzing the
entire scat using sieves of different sizes and by hand-sorting. The volume was then estimated to the
nearest 1ml using the water displacement method. Plant matter was identified up
to species level using seeds. The
animal matter was broadly classified into ants, termites and beetles. Those food items that could not be
identified were segregated into unidentified plant and animal matter. The
contribution of individual species to the diet was calculated using percent
volume method (the total volume individual food item/total volume of all food
items × 100).
Estimation
of digestible and indigestible fruit contents: Based on
the fruit remains observed in the scats during the present study (n = 474) and
the earlier study by Baskaran et al. (1995) (n =
567), important fruit species eaten by Sloth Bears were listed and these
include Cassia fistula (17.6%), Zizyphus mauritiana (15.7%), Cordia domestica (4.5%), Grewia tiliifoila (2.1%), Z. oenoplia (2.8%), Lantana camara (1.5%),
and G. hirsuta(0.11). Fresh samples of important
fruit species were collected from fruit trees and shrubs representing different
habitat/microhabitat conditions. A
total of 15-20 (or in case of tiny fruits like Lantanacamara up to 50) fruit samples of various size
classes (small, medium and big) and conditions (semi-ripe and ripe in case of C.
fistula including dry fruits) were collected from multiple plants
representing diverse micro- and macro-habitats. The digestible (fruit pulp) and indigestible fruit parts
(seeds and pericarp) were separated from each fruit
species using a scalpel. The
volume of indigestible fruit remains was estimated using the water displacement
method and the dry weight of the digestible fruit pulps by using a physical
balance after air-drying the samples separately for each fruit species. The indigestible food remains were
quantified using the volume displacement method similar to that used to
quantify the indigestible food remains from the scat, while the digestible
matter was quantified using dry weight method, as this method allowed us to
overcome the differential water content in different fruit species. Later, using the details of dry weight
of digestible fruit pulp/volume of indigestible food remains, we arrived at the
dry weight of the fruit pulp consumed in each species by the bear based on the
standard volume of indigestible fruit remains of each species segregated from
the scat.
The difference in the contribution of
various food items estimated, based on two different methods was tested for
statistical significance employing chi-square analysis using the estimated
contribution by indigestible fruit remains as the observed value and the
estimated contribution by digestible fruit remains as the expected value.
Results
The
percent contribution of various major fruit species, when estimated using the
two methods (Table 1), shows a significant difference. For example, during dry season, Cassia fistula drops from being the highest (51.1%)
contributor based on percent volume of indigestible fruit remains moves to the
second highest (30.56%) position based on dry weight method of digestible fruit
remains. Zizyphus mauritiana, on the other hand, moves from the second
position (44.1%) to the first (57.9%) on dry weight method of digestible fruit
remains. The observed difference in percent contribution of various food items
arrived using the two methods varied significantly (X2 = 24.0, df = 4, p <
0.001). Although, during the
wet seasons, the ranks do not change between the methods, the relative
contributions varied significantly (first wet season X2 = 48.5; df = 3; p < 0.001 and second wet season X2 =
17.8; df = 3; p < 0.01). For example, in the first wet season,
the contribution of Cordia domestica to the diet increased from 59.6 to 93.8 % and
that of Grewia tiliifolia dropped from 27.4 to 4.2 % by dry pulp method
instead of the percent volume method of indigestible fruit remains. Similarly,
in the second wet season, the contribution of Z.mauritianadropped from 25 to 16.36% while that of Z.oenopliaincreased from 52.5 to 71% when the dry pulp method of estimating percent
contribution to the diet was used instead of the percent volume indigestible
fruit remains method.
Discussion
The differences between the methods are
significant and warrant attention. We feel that the use of digestible food dry weight method is a much
better and more accurate method to evaluate the diet of sloth bears. The method basically requires an
adequate sample of each diet item be evaluated, to estimate the volume of
indigestible matter that is required to produce a given dry weight of
digestible matter. Once the
conversion figures are available, the scats can be analyzed for the volume
(indigestible) of different food items and these volumes can later be converted
to dry weight of digestible matter using the conversion figures derived
earlier. The problem of analyzing
the animal matter in a similar fashion also needs to be developed, preferably
under captive conditions, whereby it is easy to quantify the digestible versus
indigestible matter of insect remains with known quantum of insect food fed to
the captive bears and establish a similar conversion figure for various insect
foods. In future, the studies on
the diet of Sloth Bears (and other species with similar feeding habits) should
be analyzed using the dry weight of digestible matter derived from the volume
of indigestible matter in the scat, as this will give us a much more accurate
means of estimating the contribution of various food items to the diet.
References
Baskaran, N. (1990). An ecological investigation
on the dietary composition and habitat utilization of Sloth Bear (Melursus ursinus)
at Mudumalai Wildlife Sanctuary, Tamil Nadu (South
India). M.Phil. Thesis, A.V.C.College,Mannambandal, Tamil Nadu, India, vi+57pp.
Baskaran, N., N. Sivaganesan& J. Krishnamoorthy (1997). Food habits of the Sloth
Bear in Mudumalai Wildlife Sanctuary, Tamil Nadu,
Southern India. Journal
of the Bombay Natural History Society94(1): 1–9.
Desai,
A.A., N. Baskaran & S. Venkatesh(1997). Behaviouralecology of the Sloth Bear (Melursus ursinus) in Mudumalai Wildlife Sanctuary and National Park, Tamil Nadu.Technical Report. Bombay Natural History Society, Bombay, India
Gokula, V. (1991). Some aspects on the feeding
habits of the Sloth Bear (Melursus ursinus) at Mundanthurai Wildlife Sanctuary, Tamil Nadu (South India).M.Sc., Dissertation. A.V.C.College, Mannambandal, Tamil Nadu, India, 48pp.
Gokula, V., N. Sivaganesan & M. Varadarajan(1995). Food habits of Sloth Bear (Melursus ursinus)
in Mundanthurai Pleteau,
Tamil Nadu. Journal
of the Bombay Natural History Society92: 408-410.
Joshi,
A.R., D.L. Garshelis & J.L.D. Smith (1997). Seasonal and habitat related diet of Sloth
Bears in Nepal: Journal
of Mammalogy 78(2): 584–597.
Laurie, A. & J. Seidensticker (1977). Behavioural ecology of the Sloth Bear (Melursus ursinus). Journal
of Zoology London 182: 187–204.
Schaller,
G.B. (1967). The Deer and Tiger: A
Study of Wildlife in India.University of Chicago Press, London, viii+370pp.