Food and
foraging preferences of three pteropodid bats in southern India
Email: 1 sudhakaranmr@gmail.com (corresponding author), 2 dossanand@gmail.com
Date of publication (online): 26 January 2012
Date of publication (print): 26 January 2012
ISSN 0974-7907 (online) | 0974-7893 (print)
Editor: C.
Srinivasulu
Manuscript
details:
Ms # o2227
Received 02 June 2009
Final received 19 July 2011
Finally accepted 20 December 2011
Citation: Sudhakaran, M.R. &
P.S. Doss (2012). Food and foraging preferences of three
pteropodid bats in southern India. Journal of Threatened
Taxa 4(1): 2295-2303.
Copyright:© M.R. Sudhakaran &
Paramanantha Swami Doss 2012. 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.
Author
Details: Dr. M.R.
Sudhakaran is an Assistant Professor in Zoology at Sri Paramakalyani
College, doing research work on bats for the past ten years. He completed his
doctoral research in the year 2007 on the behaviour and distribution of Pteropus giganteusin Thamiraparani region.
Dr. Paramanantha
Swamidoss is a young scientist at Madurai Kamaraj
University, doing research on ethology of bats for the past 13 years. He is
presently engaged in doing research on the genetical aspect of C. sphinx.
Author
Contribution: Both authors contributed equally to the study.
Acknowledgements: Financial support given by UGC to Dr.
M.R. Sudhakaran is greatly acknowledged.
Abstract:A study on the
food, foraging and flight height in three species of pteropodid bats, namely Cynopterus
sphinx, Rousettus leschenaultii and Pteropus
giganteus was conducted in Tirunelveli and Tuticorin districts of
southern Tamil Nadu, India. A
total of 37 species of plants were identified as potential food plants of the
pteropodid bats. The preference
for fruits by pteropodids varied according to the developmental stages of
fruits namely, immature, unripe and ripe. There is a relationship between the foraging activities of bats and the
moon phase. Bats exhibit a varied
foraging pattern and flight height. A variation in the foraging flight height was observed in C. sphinx and R.
leschenaultii. R. leschenaultii was observed to have a higher
foraging echelon than that of the C. sphinx. In our study we found that the C. sphinxforages
normally at canopy level (up to 3.5m), R. leschenaultii forages at upper
canopy levels (up to 9m) and P. giganteus at a height
above the canopy area (>9m).
Keywords: Flight height, food preference, foraging, phenology.
INTRODUCTION
The
feeding habits of bats as a whole are as varied as that of other mammals, and
this dietary variation is proportional to much of the morphological,
physiological and ecological diversity seen in bats (Altringham 1996). Most of the bats are relatively
stereotyped in their foraging preferences. Pteropodid bats are usually frugivorous but very rarely
insectivorous where as all other bats are exclusively insectivorous (Hill &
Smith 1986). It has been estimated
that approximately 29% of the bats, partially or wholly, are dependent on
plants as a source of food (Fleming 1982).
Pteropodids
are known to be virtually phytophagous; studies also reveal that the diet of
fruit bats includes several other floral resources (largely nectar and pollen
but also petals and bracts), fruits (i.e. any plant material surrounding
seeds), often the seeds themselves and leaves (Marshall 1985). In addition to seasonal patterns of
fruit availability, frugivorous bats face highly inter-specific variations in
the timing and amount of food production (McKenzie et al. 1995). Although individual species have
restricted fruiting seasons, several species of bat eat fruits that are
generally available at all times of the year in tropical habitats. Food resources exploited by bats vary
widely in their spatio-temporal distributions (Fleming 1982; McKenzie et al.
1995; Hodgkinson 2001). In
addition to playing an important role in determining the structure of tropical
bat communities, frugivory and nectarivory reflect plant adaptations, which
facilitate seed dispersal and pollination. Bats have been found to have various foraging strategies
from the gleaning level to the aerial hawking level of flight. The factors for the flight of bats were
well discussed by Fenton et al. (1987) and Norberg & Rayner (1987).
This
paper deals with the phenology of bat depending plants and the foraging
patterns of the pteropodid bats including, C. sphinx, R.
leschenaultiiand P.
giganteus. Plant parts preference and seasonal
availability of the food has also been discussed.
MATERIALS
AND METHODS
The
study on the food, foraging and flight height of three species of pteropodid
bats was conducted from May 2008 to April 2009 in Tirunelveli (0808ÕN
& 77054ÕE) and Tuticorin (08045ÕN & 78013ÕE)
districts of southern Tamil Nadu. In this study, plants that provide food to frugivorous bats, foraging
pattern and flight height in pteropodid bats were assessed.
Weekly
field trips were made to observe the wide range of foraging habitats of
bats. Observations were made to
find the food items preferred by bats. Food remnants viz., chewed fruits, bolus
and floral remnants were collected from the bat flyways and below the day and
night roosts. The collected
remnants were analyzed to identify the plant species. The Phenology of the fruits and flowers preferred by bats in
the study area were observed and their seasonal availability was assessed. Preference of fruits in various stages
of development (immature, unripe and ripe) by bats was observed for a few
species of plants throughout their fruiting seasons. Variations in the foraging strategies and foraging bouts
among the frugivorous bats were also studied. The influence of moonlight on the foraging pattern of the
frugivorous bats was estimated.
The
flight height of pteropodid bats in the foraging area (orchards and wild trees)
was studied by using the mist netting sampling method. The foraging areas of fruit bats were
classified into two types. One is
below the canopy level (below 3.5m height) and the other is above the canopy
level (which is above 3.5m height). For capturing C. sphinx and R. leschenaultii, mist nets (Avinet
Dryden Inc. USA) with a mesh size of 3.5 x 3.5 cm were used and for capturing P.giganteus, nets with a mesh
size of 16 x 16 cm were used (custom made mist nets). Apart from the bats captured through the mist nets, bats
that came to the foraging trees were also monitored and noted. The fruiting trees for netting were
selected in a manner that would be preferred by the three species of
frugivorous bats and also where their diurnal roosting site was nearer to the
foraging area. The mist netting
exercise commenced about half an hour before dusk and was completed at 0600hr
in the morning. Mist nets were
erected from a height of 1.5Ð30 m and the bats captured at various
netting heights were recorded. The captured bats were classified according to
their age, sex and reproductive status. Captured bats were marked with a special kind of necklace (Issac et al.
2003), kept in a cage and released before dawn.
RESULTS
A
total of 37 species of food plants were identified. These plants provide fruits
or their parts, leaves, flowers, nectar and pollen for pteropodid bats
including Cynopterus
sphinx,Rousettus
leschenaultiiiand Pteropus
giganteusin the study area (Table 1).
Food
of pteropodid bats
The
bats fed on fruits, leaves, nectar and pollen. A variation of food selection
was observed within the pteropodid bats. Out of the 37 species of plants in the study area, C. sphinx was found to depend
on 35 species of plants, R. leschenaultii was found to depend on 27 species of
plants and P.
giganteus depended
on 23 species of plants for their diet during different seasons of the
year. Out of the 35 species of
plants preferred by C. sphinx, 27 provide fruits, four provide
leaves, one provides flowers, one provides leaves and flowers, one provides
nectar and fruit and one provides flowers and fruit. Out of the 27 species of plants preferred by R.
leschenaultii,
24 provide fruit, one provides flowers, one provides fruit and nectar, and one
provides fruit and flowers. Of the
23 species of plants preferred by P. giganteus, 20 provide fruit,
one provides leaves and fruit and two provide both flowers and fruit. In addition, R.
leschenaultiiand P.
giganteuswere observed feeding on toddy, a plant sap extract tapped from Borassus
flabelliferby the local farmers.
Fruits
preferred by bats at various stages of fruit development
A
study was made on the fruits preferred by bats at various stages of fruit
development in 11 species of plants (Table 2). Observations were conducted on the fruiting conditions of 11
species of plants preferred by the fruit eating bats in the study area. We observed that all the three pteropodid
species, C.
sphinx,R.
leschenaultiiand P.
giganteusfeeding on the ripe fruits of all the plant species (Table 2). R. leschenaultii and C. sphinx feed only on the
unripe and ripe fruits and not on immature fruits. But in contrast, P. giganteus were found to feed
on the immature fruits of Mangifera indica and they also prefer to feed on the
unripe fruits of Psidium guajava, Bassia latifolia, Ficus
religiosa,F.
benghalensis,M.
indica,Syzygium
cumini,Terminalia
catappaand Polyalthia
longifolia.C.
sphinxfeed on the unripe fruits of Muntingia calabura, S. cumini, and T. catappa. Whereas, R.
leschenaultiiifeed on unripe fruits of F. religiosa, S. cumini, T. catappa and P. longifolia.
Seasonal
availability of food of pteropodid bats
While
studying the seasonal availability of food for pteropodid bats in the study
area (Table 3), C. sphinx were found to enjoy the maximum food
availability in all the months.
C.
sphinx had
a higher frequency of food availability, between the months of March and September. R. leschenaultii were found to have a
higher frequency of food availability between the months of March and
August. P. giganteus were found to have a
moderate availability of food throughout the year and got maximum food
availability between the months of March and August (Table 3).
Foraging
patterns of pteropodid bats
A total of 16 observations (four
observations each in different moon phases namely full moon, last quarter,
first quarter and new moon) were made to study the foraging patterns of
pteropodid bats (Table 4). A
bimodal foraging pattern was observed for C. sphinx and trimodal
foraging pattern for R. leschenaultii. Foraging frequency of C. sphinx was found to be
maximum (77.3%) between 2100hr and 2200hr and between 0200hr and 0300hr. A variation in the foraging pattern was
observed in C.
sphinxwith reference to the different moon phases. During the full moon phase and the first quarter phase the
activity was found to be minimal compared to the other two moon phases. R. leschenaultii was found to forage
most (76.8%) with foraging bouts between 2100hr and 2200hr, and between 2300hr
and 0000hr and later between 0300hr and 0400hr, and also show a variation in
the foraging pattern similar to C. sphinx with regard to the
moon phase. P. giganteus were found to have a
variation in the foraging pattern and fed throughout the night; generally the
foraging activity was not affected by the moon phase. Even though P. giganteus fed throughout the
night, the maximum activity was observed between 1930hr and 2100hr, later
between 0000hr and 0100hr and then between 0300hr and 0400hr.
Foraging
flight heights of pteropodid bats
A
total of 37 mist netting sampling nights were spent to observe the foraging and
flight height of the pteropodid bats in the study area. Ten mist nets of large mesh size were
used to capture P. giganteus and 15 and 12 mist netting sampling
nights to capture C. sphinx and R. leschenaultii above and below the
canopy level respectively. C. sphinx, R.
leschenaultiiand P.
giganteuswere found to have a profound difference in their foraging ability and foraging
heights. C. sphinx were captured from a
height of 1.5Ð21 m and capture was maximum only below the canopy level
(> 3.5m). R.
leschenaultiiwere captured from a height of 2Ð23.5 m and they were captured more at a
height of 3.25Ð4.25 m. P. giganteus were observed
foraging at a height of 8 ft above the ground level to the height of the
foraging tree.
Even
though C.
sphinx was
captured at a height of 1.5Ð21 m, a variation in capture heights with
regard to the age and sex was observed. Of the 499 individuals of C. sphinx captured, 318
individuals were captured below the canopy level and 181 individuals above the
canopy level. The capture rate of
juvenile male (n = 46), male and female subadults of C. sphinx were found to be
maximum above the canopy level than the adults (Table 5). Capture height between the juveniles,
subadults and adults among the male and female bats of C. sphinx were not
significantly different (Kruskal-Wallis Test, p > 0.05). Capture heights
between the subadults of male and female bats of C. sphinx were significantly
different (Mann-Whitney Test; p < 0.05).
In
the case of R.
leschenaultii,
a total of 132 bats were captured. Out of this, 54 individuals were captured
below the canopy level and 78 individuals were captured above the canopy level
(> 3.5m). Of the 78 bats that
were captured above the canopy level, 34 individuals belonged to the juvenile
and subadult age groups and were observed to fly over a height of 10m, Whereas
the capture of adults bats of R. leschenaultii was minimum above a
height of 10m ( Table 5) / strike the line.
P. giganteus were observed not to
have any alteration in the foraging pattern and flight heights with regards to
age and sex. P. giganteus were mainly found to
be voracious feeders and fed throughout the night, foraging mostly at the
height of the mid crown regions to the top regions of the fruiting tree. Usually P. giganteus were not observed to
forage below 2.5m.
DISCUSSION
Frugivorous
bats exhibit two patterns of foraging behaviour with reference to plants. They are Ôsequential specializationÕ
and Ôindividual generalizationÕ. Sequential specialists use only one plant at a time but change food
sources after several days or weeks (Colwell 1974). Individual generalists will visit several species of plants
for nectar, pollen or fruit in one night. Observations made in our study corroborates with similar observations of
Gardner (1977) that the individual-general pattern appears to be common among
bats for whom fruits and flowers are major parts of the diet.
Foraging
studies of pteropodids in Tirunelveli District revealed that 37 species of
plants were observed to provide food for pteropodid bats. Bats in our study exhibited variations
in their diet selection and preference. The diet preference in bats was mainly based on the morphological and
palatable characters of the fruit (Corrlet 1996). Certain fruits may have a hard outer coat, which may be
difficult to eat for certain small frugivores, certain fruiting trees may not
facilitate the flying movements of some bats, but it may be preferred by
others. Such a variation in the
diet strategy may help the bats to avoid competition amongst themselves. Dietary selection in frugivores was
documented by several authors (Fleming & Heithaus 1981; Tidemann &
Nelson 1987). Fruits that are hard
to carry to the night roost and some other fruits that are available above the
foraging heights were normally less preferred by some bats, but bats that could
overcome such obstacles preferred those fruits. Flying foxes are postulated to have a taste preference with
reference to the selection of their food (Marshall 1983; Tidemann & Nelson
1987) which may be a reason for seasonal preference of fruits by these
pteropodid bats. P. giganteus and C. sphinx prefer to feed on
the leaves.
Folivory
in C.
sphinx(Bhat 1994) and the nutrient analysis in leaves fed by C. sphinx were well expressed
(Ruby et al. 2000). P. giganteus were observed to feed
only on the leaves of Ficus religiosa. Lowry (1989) refers to the phenomenon Ôgreen leaf fractionationÕ whereby
whole leaves are seldom consumed, but chewed and the whole liquid extract is
consumed. A large amount of bolus
of F.
religiosawas collected and was observed to be a regular in the diet of P. giganteus. P. giganteus and R.
leschenaultiiwere observed to drink ÔtoddyÕ, which may be similar to that of the P. mariannus licking water from
the surfaces of leaves as a supplement for moisture and nutrient requirements
as observed by Wiles et al. (1991).
Observations
on the diet selection in pteropodid bats revealed that they fed on unripe
fruits, mature fruits and immature fruits. The main cause for this may be the low availability of
resources and competition for other fruits. Certain orchard fruits were observed to be fed on in
immature and unripe stages, this may be due to the nature of palatablity. Wiles & Fujita (1992) reported that
the flying foxes in the Pacific Islands fed on the cultivated plants at stages
of fruit maturity. Jacobsen &
DuPlessis (1976) reported that Rousettus aegyptiacus fed on green figs
that were hard to crush at times, when there was a scarcity of availability of
food.
On
studying the seasonal availability of food for the pteropodid bats, C. sphinx were observed
enjoying a wide variety of food availability. It may have been because of their flexibility in food
selection or also of opportunistic food choice. P. giganteus were observed to have lesser fruit
choice and availability throughout the year. Most of the Pteropus species were
observed to commute longer distances for their foraging activity (Nelson
1965). Similarly P. giganteus were also observed to
be long distance foragers (Goyal et al. 1993) to fulfill their dietary
requirements and also makes it an opportunistic feeder. On studying the diet availability for
bats in various months of the year, the maximum availability of food was during
their breeding periods and bats switched over to different food items according
to their availability. The
reproductive periods of bats are ultimately determined by food availability
(Marshall 1985). The timing of
reproductive events among plants (flowering and fruiting) may influence the batÕs
reproductive cycles, foraging patterns and the intensity of competition for
food resources among bat species (Heithaus et al. 1975).
In
case of plant-visiting bats, resource abundance and distribution pattern appear
to significantly influence foraging group size. This point was well illustrated by the behaviour of Phyllostomus
discolor (Heithaus
et al. 1974; Sazima & Sazima 1978). The feeding group size of P. discolor declines as the
number of flowers per plant declines (Fleming 1982). A similar pattern of foraging activity was also observed in R.
leschenaultiiand P.
giganteus. Howell (1979) argues that the main
advantage of flock foraging was that it increases individual foraging
efficiency on patchily distributed flowers. Species like Artibeus jamaicensis and Phyllostomus
hastatusfly in groups, but both are also solitary foragers (Goodwin & Greenhall
1961).
C.
sphinxwas observed to show a bimodal foraging pattern, while R.
leschenaultiiishowed a trimodal foraging pattern. Bats probably exemplify various modes of foraging patterns, the first
peak is at the beginning of the foraging activity and the second peak towards
the end (Erkert 1982). Unlike C. sphinx and R.
leschenaultiii,P.
giganteuswere observed to be voracious feeders, feeding throughout its foraging
activity.
The
foraging patterns in bats were observed to be affected by the moonlight and
environmental factors (Kunz 1982). The pattern of foraging in C. sphinx and R.
leschenaultiialtered at a greater rate depending on the moon phase. C. sphinx showed a decreased
pattern in its foraging activity during full moon (Elangovan & Marimuthu
2001; Singaravelan & Marimuthu 2001). The reason for this may be the that the bats protect themselves from other
predators (Nair et al. 1998).
A
variation in the flight height was observed in C. sphinx and R.
leschenaultii.
R.
leschenaultiiwas observed to have a higher foraging echelon than that of the C. sphinx. In our study C. sphinx foraged normally at
the canopy level, R. leschenaultii foraged at upper canopy levels and P. giganteus above the crown area
at a greater rate. The variation
in foraging height of R. leschenaultiii may be mainly determined by the wing
loading and the aspect ratio (Fenton et al. 1987; Elangovan et al. 2004). The variation in the foraging height
also helps the bats to have different foraging strategies, flight mode and food
preferences. This strategy helps the bats to utilize the resources to a greater
extent. In our study, apart from
the regular foraging heights, bats were also observed to engage in foraging
guilds at various heights; such conditions were observed to exist only when the
fruit availability was low. The
observation made by us is similar to that by Cosson (1995), who studied the
pteropodid bat flight
activity level under forest canopy in southern Cameroon and reported that small
frugivores feed on the understorey low lying fruits whereas large frugivores
feed on the fruits in the upper canopy level.
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