Frugivory, Seed Dispersal and Regeneration by Birds in South Indian Forests

21 Pages·2003·12 MB·

by  P Balasubramanian

FRUGIVORY, SEED DISPERSAL AND REGENERATION
BY BIRDS IN SOUTH INDIAN FORESTS
(With seven text-figures and one plate)
P. Balasubramanian1’2 and B. Maheswaran1
Key words: Tropical forest, bird-fruits, avian frugivores, seed dispersal, fruit size,
forest regeneration, Western Ghats
Plants, unlike animals, are immobile and have little control overthe choice ofsite where they can live and grow.
Over aeons, plants have perfected the art ofsurvival in spite ofthis disability by steadily interacting with the
animals in their habitat. The evolution ofbrilliant, attractive colours and endowment ofthe fruits with nutritious
supplements such as proteins, lipids and carbohydrates, have appealed to the dietary needs of birds and
mammals. Furthermore, the plant’s ability to asynchronously produce fruits, for the assemblage ofvertebrates
dependent on fruits have made their dispersal possible. Plant-bird interactions play apivotal role in maintaining
the structural and functional integrity ofnatural ecosystems. Also, the interactions guide the process ofevolution
ofbiodiversity aswell as ecological communities. On account oftheirunparalleled richness, tropical communities
aretreasuretrovesofbiological interactions betweenplants and animals. Ecological degradations, as in shrinking
habitats and fragmentation, necessitate acomprehensive understanding ofthe basic tenets ofinteracting entities,
in order to evolve effective strategies to preserve and enrich our biodiversity.
Introduction physiological and anatomical modifications to
process the fruit diet have been the key in the
Birds play a prominent role in pollination contemporaneous plant-bird interactive relations.
and seed dispersal ofplants. The flower visiting Such persistent relationships have given rise to
birds, while harvestingnectar, pollinate their food mutual dependence, benefiting both elements.
plants. Similarly, the fruiteatingbirds by devouring Though fruit-frugivore interactions have
the pulpy fruits distribute the seeds oftheir food been studied by various authors during recent
plant species. Birds, by virtue oftheir habits, can times, there is no consolidated information on the
play a more effective role in seed dissemination role of birds in seed dispersal and forest
than otheranimals. Compared to othervertebrates, regeneration. Information is available on the fruit
which disseminate the seeds in clumps, the seed types consumed by various bird species in India,
deposition pattern ofbirds is more efficient. The but only a few studies attempted to quantify the
A
interactionsbetween flower-birds andbird-flowers role of birds in forest regeneration. review of
have been discussed (Ali 1931, Subramanya and those studies and reference to the various floras
Radhamani 1993). A variety ofbirds and mammals indicate that several families benefit from birds
depend predominantly on fruit to fulfil their fortheir regeneration. Known syndromes ofbird-
nutritional requirements. Such fruit-eating birds dispersed fruits help to identify various bird-fruits
and mammals are termed as frugivores. Fruittraits from hitherto unexplored bird habitats.
such as colour, size and nutritional supplements Frugivores help seeds escape from the
have evolved in response to interacting deleterious effects ofseed and seedling predators
vertebrates. The evolution of fruit syndromes, (Janzen 1970). Differences in frugivore activity
complemented by the birds’ adaptive ability to have profound effects on the conditions under
recognise these syndromes, along with which seeds and seedlings must survive, and
consequently should influence the evolution of
‘Salim Ali Centre for Ornithology and Natural History
tree demographies. The relationship between seed
(SACON),
Coimbatore 641 108, Tamil Nadu, India. dispersal and seedling demography has profound
2Email: [email protected] implications for tropical conservation policy
JOURNAL BOMBAY NATURAL HISTORY SOCIETY, 100(2&3), AUG.-DEC. 2003 411
.
FRUGIVORY IN SOUTH INDIAN FORESTS
(Howe 1984). Seasonality in fruit production in frugivorous species, Psittacidae (parrots) and
tropical forest ecosystems has brought to light Capitonidae (barbets; Plate Fig. hold 5 species
1, 1)
the roles played by ‘keystone’ or ‘pivotal’ species each. Among the 66 species offruit-eating birds,
during periods ofscarcity. members of Columbidae (except the mountain
Studies on fruit-frugivore interactions imperial-pigeon) and Psittacidae (parrots) digest
conducted by us as part ofresearch programmes the seeds and hence are considered as seed
under the Bombay Natural History Society predators. Other frugivores could be considered
(BNHS) and the Salim Ali Centre for Ornithology as legitimate seed dispersers.
and Natural History (SACON) for the past two The body size varied considerably among
decades helped us to arrive at certain conclusions frugivorous birds (range 5-2,500 g; Appendix I;
and also comprehensively list the plant genera Fig. 1). Hombills (Family Bucerotidae) were the
dispersed by birds in south India. The material heaviest birds, having a mean body weight of
for this paper has been derived mainly from the 1,246 g(n=3) followedbyFamilyCorvidae (crows)
Tropical Dry Evergreen Forests ofPointCalimere, and Columbidae (pigeons) whose mean body
and the Semi-evergreen, Dry and Mixed weight was 288 g (n=4) and 246 g (n=7)
Deciduous Forests ofthe Western Ghats. Though respectively. The great pied hornbill Buceros
seed dispersal is effected by exozoochorous bicornis, a charismatic flagship species of the
methods (dispersal effected by seeds clinging on Western Ghats and northeastern India, is the
to body parts ofbirds and animals) also, we would heaviest among frugivores, weighing 2,500 g
like to state thatthe review exclusively deals with followed by Malabar pied hornbill Anthracoceros
endozoochory (dispersal wherein fruits are coronatus (1,000 jungle crow Corvus
g),
ingested, the pulp digested and the seeds macrorhynchos (650 g) andthe mountain imperial
defecated or regurgitated). -pigeon Ducula badia (580 g). Hornbills and
pigeons are also voracious frugivorous bird
Observations species in their habitat.
35
Frugivory and seed dispersal in south India
The present review is based on three major
research efforts in south India - on the Tropical
Dry Evergreen Forests in Point Calimere, Dry
Mixed Deciduous Forests ofCoimbatore Division
and Semi-evergreen forests ofMudumalai Wildlife
Sanctuary (MWLS), Western Ghats. The lists of
fruit-eating birds and bird-dispersed fruit species 0-50 50-100 100- 150- >200
have been compiled chiefly fromthesethree major 150 200
studies and have been summarised in Appendix I Body mass
(g)
and
II.
A total of66 species (36 genera) ofIndian Fig 1 : Body mass offrugivorous birds in south
Indian forests (n=66)
birds from 16 families have been documented for
frugivory in south India. Bird species offamilies Bird attracting flora in south India
Columbidae (pigeons), Pycnonotidae (bulbuls) Fruits of219 species (141 genera) belong-
and Muscicapidae (flycatchers) contributed the ing to 61 plant families were recorded to be used
maximum number of frugivorous species (7 by frugivorous birds. The members of the
species). While Sturnidae (mynas) hold 6 families Lauraceae (21 species), Euphorbiaceae
412 JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, 100(2&3), AUG.-DEC. 2003
FRUGIVORY IN SOUTH INDIAN FORESTS
Balasubramanian, P. et al Species involved in frugivory in Western Ghats Plate 1
MARUDHACHALAM
K.
Fig. 1: Coppersmith barbet Megalaima haemacephala, a frugivore and major seed
disperser of forest trees, at Coimbatore Forest Division
BALASUBRAMANIAN
P.
Fig. 2: Ficus benghalensis, a keystone species for avian frugivores, in the Coimbatore
Forest Division
JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, 100(2&3), AUG.-DEC. 2003 413

FRUGIVORY IN SOUTH INDIAN FORESTS
120
and Zizyphus were represented by 4 species each
(Appendix
II).
The fruit types ofall the 219 species were
determined. Berries were the predominant fruit
type borne by 99 species (45%) while drupes were
borne on 76 species (35%) and together
accounted for 80% ofthe fruits for the whole of
south India (Fig. 2). Fleshy-ffuited plants are very
common in tropical forests, with frequencies
usually over 70% (ofwoody plants) in the forests
and lesser in the dry forests. The frequency of
fleshy-ffuited plants in the Dry Deciduous Forests
Berry Drupe Capsule Syconium Others of Coimbatore was 65%, while in Tropical Dry
FruitTypes Evergreen Forests ofPoint Calimere was 73%.
it
Fig. 2: Morphological classification ofbird-dispersed In the Semi-evergreen Forest of Mudumalai
fruits in south Indian forests (n= 219) Wildlife Sanctuary, Western Ghats, 57% of the
(13 species), Rubiaceae (12 species), Moraceae species and 74% ofindividuals were fleshy-ffuited
(10 species), Meliaceae and Annonaceae (9 species.
species each) were most represented among Colours ofripe fruits for all the 2 19 species
fleshy-ffuited species adapted for ffugivory. The were assigned to one of eight broad colour
genus Ficus (figs), known for their ability to categories as used by Wheelwright and Janson
produce fruits asynchronously and support the (1985). The analysis showedthat 94 species (43%)
ffugivore community during periods of scarcity, produced black fruit while 58 species (26%)
was represented by 8 species. The genera produced red fruit and 39 species (1 8%) produced
Eugenia and Litsea were represented by 5 species yellow fruit (Fig. 3). Black and red accounted for
each, while Capparis Cinnamomum Diospyros 70% ofspecies.
, ,
a)
a>
o
a)
a.
</)
Colour
Fig. 3: Colours ofbird-dispersed fruits in south Indian forests (n=219)
JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, 100(2&3), AUG.-DEC. 2003 415
FRUG1VORY IN SOUTH INDIAN FORESTS
Analyses ofthe fruit diameter revealed that bulbul Pycnonotus luteolus red-vented bulbul
,
98 species (45%) had their fruit sizes 10-20 mm, Pycnonotus cafer jungle myna Acridotheres
,
while another 85 species (39%) bore fruits in the fuscus brahminy starling Sturnus pagodarum
, ,
size range <10 mm. Only 36 of the 219 species jungle crow Corvus macrorhynchos, house crow
mm
(16%) bore fruitsofsizegreaterthan20 (Fig. 4). Corvus splendens and Asian koel Eudynamys
About 83% of fruits were less than 20 mm in scolopacea Other seed dispersers included rosy
.
diameter. Plants of Families Annonaceae, starling Sturnus roseus, Eurasian golden oriole
Burseraceae, Elaeocarpaceae, Meliaceae, Oriolus oriolus, Indian tree pie Dendrocitta
Moraceae and Myristicaceae produced large fruits vagabunda, jungle babbler Turdoides striatus
while plants of Families Cucurbitaceae, and Tickell’s flowerpecker Dicaeum
Cordiaceae, Ebenaceae, Lauraceae, erythrorhynchos Pycnonotus luteolus visited
.
Melastomataceae, Menispermaceae, Oleaceae maximum number of plants (63), followed by
and Rubiaceae produced small fruits. Pycnonotus cafer (51), Eudynamys scolopacea
(32) and Acridotheres tristis (27). Three plant
species were visited by more than 0 bird species.
1
120 Salvadora persica was visited by maximum
i
number of bird species (15), followed by
Manilkara hexandra (12) and Ficus infectoria
01
).
Even though nearly 50% of the fleshy-
fruited species in Point Calimere were consumed
by mammals, only 0% ofthe species were solely
1
dispersed by mammals. Most plant species are
chiefly dispersed by birds.
<10 10-20 20-30 >30
Sizeclass (cm) Birds and natural regeneration in Dry Mixed
Deciduous Forest, Western Ghats
Fig. 4: Fruit size classification ofbird-dispersed In an effort to understand the tenets of
fruits in south Indian forests (n=219)
restoration ecology with birds as the basis of
SACON
regeneration, a project was launched by
Birds and regeneration in Tropical Dry in cooperation with the Tamil Nadu Forest
Evergreen Forest,south India Department. The studies were conducted in the
A study on the interrelationships between Dry Mixed Deciduous Forest, Coimbatore Forest
fleshy-fruited plants and their vertebrate Division, Western Ghats (Balasubramanian et al.
consumers was conducted in the Dry Evergreen 1998). Ofthe 1 15 woody species recorded in the
Forest in Point Calimere, south India in the mid- study area, 52% of the species were bird-
1980s (Balasubramanian 1996). Duringthe course dispersed. Figs attractedmaximum numberofbird
ofthe study, 3 7 species offlowering plants were species followed by Celtis philippensis and
1
recorded, of which 88 bore fleshy fruits. Sixty- Syzygium cumini Of the 35 fruit-eating bird
.
four ofthe 88 fleshy-fruited species were adapted species, 18 (51 .42%) were major frugivores. The
A
for frugivory by birds. total of20 bird species red-vented, white-browed and red-whiskered
of14 genera from 10 families were observed to eat bulbuls were most frequent visitors to fruit trees
fruits at Point Calimere. The major avian seed in the Dry Deciduous Forest. Inthe riverine forest,
dispersers documented were the white-browed barbets, bulbuls, mynas, the Asian fairy bluebird
416 JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, 100(2&3), AUG.-DEC. 2003
FRUGJVORY IN SOUTH INDIAN FORESTS
and koel were major frugivores. The Malabar pied regeneration potential, represented by more than
hornbill, one ofthe largest frugivores ofthe Indian 10 saplings. In the highly degraded habitat, only
subcontinent, were seen to feed on fruits ofFicus 3 out of9 species had more than 10 saplings.
sp., Strychnos nux-vomicaand several other large-
fruited species in the riverine forest Hornbills and forest regeneration in Semi-
(Balasubramanian and Saravanan 2001). evergreen and Evergreen Forests
Five species, namely Ficus benghalensis Malabar grey hornbill Ocyceros griseus
, ( ),
F. racemosa Celtisphilippensis Cassineglauca an endemic frugivore of restricted range in the
, ,
andStrychnospotatorum were experimented with moist forests of Western Ghats, south India, is
,
to determine if the birds enhanced germination dependent on fruit resources and suitable nest
capacity of seeds that passed through their trees for subsistence. As a consequence of its
intestinal tracts. The germination percentage of specialised breeding habits and dependence on
seeds dispersed by birds was significantly higher fruits as a predominant source of food, this
than that of the seeds collected from plants for hornbill is known to interact with a variety oftree
four species. In one species Celtis philippensis species. The Malabar grey is considered one of
,
although a similar trend was observed, the the keystone species and a major seed disperser
difference was not significant (Fig. 5). in the Western Ghats region (Mudappa 2000).
Natural regeneration of bird-dispersed Like most otherhornbills, the Malabar grey
plants was studied in the Dry Mixed Deciduous is known to bring a large load offruittothe nesting
Forests of Coimbatore Division in Tamil Nadu. site to feed the incarcerated female and chicks
The density of seedlings and saplings of bird- during the breeding season. Seeds of fruits
dispersed trees varied from 279 perhectare in the consumed are squirted out through the nest slit,
highly degraded habitatto 640 in the undisturbed and get embedded in the litter-strewn forest floor.
habitat. Twelve out of the 15 species had good These seed deposits are usuallytermed as midden.
60
Bird defecated Fresh
50
40
c
o
•*—*
OcJ
E 30
O<u
20
10
0
Ficus Ficus Celtis Cassine Strychnos
benghalensis racemosa philippensis glauca potatorum
Species
Fig. 5: Percentage germination ofbird-defecated and fresh seeds, Coimbatore Forest Division
JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, 10Q(2&3), AUG.-DEC. 2003 417
1
FRUGIVORY IN SOUTH INDIAN FORESTS
Monitoring the midden deposits and analysing selected for studying midden regeneration. Two
m
the seeds therein during breeding season, helped square plots (5 sq. each) were demarcated for
to detenninethe variety offruit species consumed each nest site, one behind and one in front ofthe
and dispersed by this hombill. The study was nest. During the post-breeding season (May-
conducted in the Semi-evergreen Forests of January), these sites were visited every week to
Mudumalai Wildlife Sanctuary (Balasubramanian study regeneration from the midden deposits.
and Maheswaran 2001). Tree species common to New seedlings of a total of 19 species
this vegetation type are Olea dioica, belongingto 13 families were enumeratedfrom the
Actinodaphne malabarica Persea macrantha square plots. Olea dioica one ofthe favoured fruits
, , ,
Cinnamomum verum, Lagerstroemia microcarpa ofthis birds wasrecorded in all the 12 midden sites,
,
and Terminalia sp. while Cinnamomum verum was recorded from 1
Ofthe 1,430 individuals belonging tothe 70 midden sites. Lauraceae and Flacourtiaceae (3
tree species present, 74% ofindividuals and 56% species each) were the most represented families
ofthe species were adapted for frugivory. Major among the regenerated seedlings. The number of
disperser species in this habitat, apart from the seedlings regenerated in front of the nest was
Malabar grey hombill Ocyceros griseus were significantly higher than those behind the nest (X2
( ),
the fruit pigeons (Ducula badia), barbets = 298.378; df = 9; P < 0.005). While 13 species
(Megalaima sp.), mynas (Acridotheres sp.) and comprising280regeneratedseedlingswererecorded
starlings Sturnus sp.). During the breeding behind the nests, 18 species comprising 761
(,
season, an intensive nest search was conducted seedlings had regenerated in front ofthe nest site,
in the semi-evergreen patches of Mudumalai just below the nest hole, i.e. 63% more seedlings
Wildlife Sanctuary for nesting activity of the regenerated infrontofthenest. Greaterregeneration
Malabar grey hornbill. Cavities oftrees used by in front ofthe nest was seen at all the sites except
hombills for nesting were located by following nest site 9 (Fig, 6). Regeneration within a species
breeding pairs ofhombills, prior to the breeding was also found to be significantly higherin front of
season. Twelve nests in the breeding season were the nest(X2=213.823; df= 8; P < 0.005).
120
100
80
co
O)
c
0
0 60
n
c
40
20
0
1 2 3 4 5 6 7 8 9 10 11 12
Nest sites
Fig. 6: Regeneration ofseeds behind and in front ofMalabar grey hombill nests in a Semi-evergreen Forest
at Mudumalai Wildlife Sanctuary, Western Ghats
418 JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, 100(2&3), AUG.-DEC. 2003
1
FRUG1V0RY IN SOUTH INDIAN FORESTS
Germination experiments were conducted Bird-aided regeneration in other forests ofthe
at the study site using seeds collected from the Western Ghats and coastal plains
midden, and control seeds ofripe fruits collected Hombills are one ofthe dominant frugivores
directly from trees for comparison. Seeds oftwo and seed dispersers ofthe palaeotropical region.
preferred fruit species, Olea dioica and Persea In the Asian tropical forests, they have been well
macrantha, were chosen for seed germination studied for frugivory, especially in the breeding
studies. The soil conditions in which the season, and are known to disperse the seeds
experimental seeds were planted were the same undamaged (Leighton 1981). Hornbills, for most
as they would be in the midden. Seeds were sown part ofthe year, are scatter dispersers, but during
in polythene bags under open conditions and the nesting season large numbers of seeds are
watered regularly. deposited under the nests, creating conspicuous
After four months of continuous middens. Our study in the Semi-evergreen
monitoring ofthe seedlings, it was observed that Forests ofMudumalai Wildlife Sanctuary, Western
bird-defecated seeds had a higher regeneration Ghats has established that the Malabar grey
potential than control seeds collected directly hornbill utilises 27 different fleshy-fruit species,
from plants. Bird-defecated seeds ofOlea dioica and 16 species were recorded to have regene-
showed 41 .67% highergermination rate than fresh rated from the midden under nest trees of
seeds while for Persea macrantha the bird- hombills. Kannan and James (1999) identified 2
,
defecated seeds showed 75% enhanced species oftrees with lipid-rich fruits, utilised by
A
germination over the control seeds (Fig. 7). hornbills Buceros bicornis and Ocyceros
(
statistical comparison ofthe bird-defecated and griseus). These included 12 Cinnamomum,
control seeds for both the species showed a 2 Myristica, 2 Beilschmedia, 2 Dysoxylum
,
significantly higher rate of germination for Persea and 2 Polyalthia species.
1
bird-defecated seeds (X2 = 90.739; df =1; In a study in the Moist Deciduous Forest
P<0.005). habitat in the Western Ghats of Kerala
(Vijayakumarand Zacharias, in press) showed that
the major frugivores were the white-cheeked
barbet Megalaima viridis crimson-throated
,
barbet Megalaima rubricapilla pompadour
,
green-pigeon Treron pompadora black bulbul
,
Hypsipetes leucocephalus and common hill-myna
Gracula religiosa.
In the Wet Evergreen Forest of Kalakad-
Mundanthurai Tiger Reserve, southern India,
birds dispersed 59% ofthe 65 fleshy-fruited tree
species (Ganesh and Davidar 2001). About 33%
(16) ofbird-dispersed species belonged to Family
Lauraceae. While small birds dispersed 86% of
the plant species, pigeons dispersed 14% oflarge
Species fruited species. The six common frugivorous
species of that habitat were black bulbul
Fig. 7: Percentage germination ofseeds defecated by
Hypsipetes leucocephalus yellow-browed bulbul
Malabar grey hornbill and control seeds, in two plant ,
species at Mudumalai Wildlife Sanctuary, Iole indica red-whiskered bulbul Pycnonotus
,
Western Ghats jocosus, white-cheeked barbet Megalaimaviridis
,
JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, 100(2&3), AUG.-DEC. 2003 419
FRUG1VORY IN SOUTH INDIAN FORESTS
mountain imperial-pigeon Ducula badia and 1998). In PointCalimere (Balasubramanian 1996),
Nilgiri wood-pigeon Columba elphinstonii. 74% ofthe visits by birds on fruiting plants were
Effects of hornbills on seeds have been by two species ofbulbuls. In the Dry Deciduous
documented for 34 species in Dja Reserve, Forests of Coimbatore (Balasubramanian et al.
Cameroon (Whitney et al. 1998). Seeds of most 1998), the largest number ofvisits (47.5%) were
species were egested without much physical by 3 species ofbulbuls followed by 3 species of
damage. Germination trials on 24 species showed barbets (18.46%). In a study in the subtropical
that 23 species germinated after egestion by two shrub lands of Hong Kong, two species of
hornbills, Ceratogymna atrata and bulbuls, the red-whiskered bulbul {Pycnonotus
C. cylindricus, and a major proportion of these jocosus and the light-vented bulbul {Pycnonotus
)
species did not exhibit a fall from the germination sinensis were the most important seed dispersal
),
rate in control seeds. agents. These species have an unusually large
A study on plant-bird interaction in the gape width for their size, and they utilise this
Tropical Evergreen Forest of the erstwhile advantage to the maximum (Corlett 1998). The
Chengalpattu district, Coromandel coast, dominantrole ofbulbuls in frugivory and dispersal
southern India, showed that 130 out of the 180 in tropical forest communities makes them a
woody plants (72%) bore fleshy fruits valuable group ofbirds.
(Narasimhan et al. 1993). Major fleshy-fruited Research on plant-bird interactions at Point
species included Zizyphus oenoplia, Allophyllus Calimere showed that conspicuous colour
serratus, Ficus benghalensis, Benkara combined with small size of fruit enabled
malabarica, Hugonia mystax, Tarenna asiatica, frugivorous birds to access fruit resources easily
Memecylon umbellatum, Carmona retusa and (Balasubramanian 1996). According to Terborgh
Dendrophthoe falcata. Though 150 birds have and Diamond (1970), small-fruited plant species
been recorded from this region (Siromoney 1971), attract more species of birds than large-fruited
only 20 are involved in seed dispersal. Families of ones. Corlett (1996) observed that most of the
frugivorous birds recorded include Columbidae, bird-dispersed seeds in Hong Kong had a mean
Cuculidae, Capitonidae, Oriolidae, Sturnidae, diameter of <13 mm. This trend was consistent
Corvidae, Irenidae, Pycnonotidae and with findings from the Neotropics (Janson 1983,
Muscicapidae. In this forest, berries and drupes Howe 1986), Africa (Knight and Siegfried 1983,
were the major fruit types encountered, while red Gautier-Hion et al. 1985), Australasia (Beehler
(48%) followed by black (31%) were the 1983, Green 1993) and in Indonesia(Suryadi etal.
predominant fruit colours. The study also showed 1994).
that 72% of the fruits were less than 1 cm in
diameter, indicating the role of generalist Birdsand enhancementofseed germination and
frugivores in dispersal. regeneration
Bulbuls have established themselves as one Frugivores affect the germination success
of the dominant frugivores and seed dispersers ofseeds which they either defecate or regurgitate,
in scrub jungles or forests of secondary as the gastrointestinal enzymes and acids within
vegetation in Asia, Africa and the Middle East the gut of the birds soften the hard seed coat,
(Lever 1987). In the Tropical Dry Evergreen, as thus breaking dormancy in seeds (Fleming and
well as Dry Mixed Deciduous Forests of south Heithaus 1981). Our study has clearly established
India, bulbuls are the predominant frugivorous the role played by birds in enhancement ofseed
and seed dispersing species (Vijayan 1975, germination in Dry Mixed Deciduous and Semi-
Balasubramanian 1996, Balasubramanian et al. evergreen Forests of the Western Ghats. Seeds
420 JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, 100(2&3), AUG.-DEC. 2003