APPENDIX - i Journal of Assam University O Vol.3(I)pp 158-169 (1998) Bird Diversity in and around Dargakona, Cachar, Assam Bivash Dev', P.C. Bhattacharya^ and Abhik Gupta^ Abstract Sixty species of birds belonging to twentysix families were recorded in and around Dargakona, Cachar district, Assam. The seasonal distribution of the different species, the habitats in which they most commonly occurred, and their frequency of occurrence in these habitats were also noted. Habitat destruction in the form of deforestaUon, especially the removal of old, mature trees as well as the degradation and reclamation of wetlands in the study area were some of the major factors responsible for a decline in bird diversity and density. A few species were also affected by hunting for sport and food. Introduction Birds have attracted human attention since time immemorial because of their beauty, their ability to fly, and their importance as a source of food and feathers. However, besides their aesthetic and economic value, birds are now being assigned high ecological 'value' because of the vital links they provide in the food chains, and the key role they play in nutrient cycling in wetlands and marine ecosystems (Golovkin, 1967; Golovkin and Garkavaya, 1975; Allaway and Ashford, 1984; Morales and Pacheco, 1986; Bildstein et ai, 1992), and their importance as general indicators of the state of the environment in which they occur (Hafner and Britton, 1983; Gole, 1987; Bildstein et al., 1990). However, before any detailed ecological investigation of the bird.s of a given area can be undertaken, it is essential that a checklist or an inventory of taxa be prepared and updated from time to time. While such studies have received fairly adequate attention in the other parts of India (Kalia and Kaul, 1976; Ali, 1983; Gole, 1987; Vyas, 1996; Subramanya and Prasad, 1996; Khachcr, 1996; Gaston and Zacharias, 1996), very litlle information is available from Northeast India, ajid more so from South Assam. The present paper provides a checklist of birds in and around the Assam University campus at Dargakona, Cachar district, Assam, and is part of a survey presently being conducted to record the avifaunal diversity in the Barak Valley districts of Cachar, Hailakandi and Karimganj. Study Area The present survey was conducted in an area located to the south of the city of Silchar (24°50 'N; 92°40 'E) in Cachar district, Assam, it covered an area of approximately 40-50 sq. km, extending from die Silcoorie Tea Estate to tlie Borjalenga and West Jalenga Tea Estates. The Silchar-Hailalcandi road runs through this area and the major habitat types include tea gardens, grassy meadows, scrub jungles, open forests, relatively dense forests on the hills dominated hy Artocarpus sp., as well as various floodplain habitats like open water zones, su-eams, swamps and marshes with emergent shrubs and other vegetation. 1 Department of Ecology, Assam University, Silctiar 788015, Assam; 2 : Department of Zoology, Gauhati University, Guwahati 781014, Assam 158
Transcript
APPENDIX - i
Journal of Assam University O Vol.3(I)pp 158-169 (1998)
Bird Diversity in and around Dargakona, Cachar, Assam Bivash Dev', P.C. Bhattacharya^ and Abhik Gupta^
Abstract
Sixty species of birds belonging to twentysix families were recorded in and around Dargakona, Cachar district, Assam. The seasonal distribution of the different species, the habitats in which they most commonly occurred, and their frequency of occurrence in these habitats were also noted. Habitat destruction in the form of deforestaUon, especially the removal of old, mature trees as well as the degradation and reclamation of wetlands in the study area were some of the major factors responsible for a decline in bird diversity and density. A few species were also affected by hunting for sport and food.
Introduction
Birds have attracted human attention since time immemorial because of their beauty, their ability to fly, and their importance as a source of food and feathers. However, besides their aesthetic and economic value, birds are now being assigned high ecological 'value' because of the vital links they provide in the food chains, and the key role they play in nutrient cycling in wetlands and marine ecosystems (Golovkin, 1967; Golovkin and Garkavaya, 1975; Allaway and Ashford, 1984; Morales and Pacheco, 1986; Bildstein et ai, 1992), and their importance as general indicators of the state of the environment in which they occur (Hafner and Britton, 1983; Gole, 1987; Bildstein et al., 1990). However, before any detailed ecological investigation of the bird.s of a given area can be undertaken, it is essential that a checklist or an inventory of taxa be prepared and updated from time to time. While such studies have received fairly adequate attention in the other parts of India (Kalia and Kaul, 1976; Ali, 1983; Gole, 1987; Vyas, 1996; Subramanya and Prasad, 1996; Khachcr, 1996; Gaston and Zacharias, 1996), very litlle information is available from Northeast India, ajid more so from South Assam. The present paper provides a checklist of birds in and around the Assam University campus at Dargakona, Cachar district, Assam, and is part of a survey presently being conducted to record the avifaunal diversity in the Barak Valley districts of Cachar, Hailakandi and Karimganj.
Study Area
The present survey was conducted in an area located to the south of the city of Silchar (24°50 'N; 92°40 'E) in Cachar district, Assam, it covered an area of approximately 40-50 sq. km, extending from die Silcoorie Tea Estate to tlie Borjalenga and West Jalenga Tea Estates. The Silchar-Hailalcandi road runs through this area and the major habitat types include tea gardens, grassy meadows, scrub jungles, open forests, relatively dense forests on the hills dominated hy Artocarpus sp., as well as various floodplain habitats like open water zones, su-eams, swamps and marshes with emergent shrubs and other vegetation.
1 Department of Ecology, Assam University, Silctiar 788015, Assam; 2 : Department of Zoology, Gauhati University, Guwahati 781014, Assam
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iaddyfields and other cultivated plots of land, bamboo groves and horticultural gardens lear villatges and the like.
Materials and Methods
The survey was conducted from March 1995 till date. Various habitats on either side of he Silchar-Hailakandi road from Silcoorie to West Jalenga tea estates were studied for the )ccurrence of birds at weekly/fortnightly intervals. From the total number of sightings in he appropriate habitats, the percentage frequency of occurrence of all the species were istimated and the taxa assigned a status of "Very rare" (1-89% of the total frequency). Rare" (10-49%), "Common" (50-89%), and "Abundant" (90-100%) (adopted with modi-ications from Gole, 1987; Vyas, 1996; Gaston and Zacharias, 1996). The seasonal distri-wtion of the various taxa were also noted. Each bird species was assigned a given habitat )r set of habitats where it was likely to be found most frequently (Gole, 1987). This does lot exclude the possibility of finding that bird in some other habitat type.
Results and Discussion
A total of 60 species of birds belonging to 26 families were recorded from the study irea. Of these, family Muscicapidae (babblers, warblers and flycatchers) with 8 species ivas the most diverse, followed by Ardeidae (herons, egrets and bitterns) with 5 species; Zluculidae (cuckoos), Stumidae (starlings and mynas), Carapephagidae (cuckoo-shrikes md minivets) and Ploceidae (weaver birds) with 4 species each; Columbidac (igeons and doves), Alcedinidae (kingfishers), Corvidae (crows, magpies and jays) and Pycnonotidae ^bulbuls) with 3 species each; Anatidae (ducks, geese and swans), Psittacidae (parrots) md Picidae (woodpeckers) with 2 species each; and the rest of the families represented by i single species each (Table 1).
Table 1 also reveals that these birds were recorded from a variety of habitats ranging from freshwater systems like ponds, tanks, beels, floodplain lakes and markshes to paddyfields, rural settlements, scrub jungles, degraded open forests and relatively dense forests on the hills. Thus spatial heterogeneity of bahitats appears to be an important factor governing the diversity iuid distribution of birds in this area. Spatial heterogeneity of habitats has long been known to be strongly correlated with the number of species found in that area. MacAriluir and MacArthur (1961) first showed that bird species diversity is positively con-elated v;iih the structural complexity of vegetation which in turn was quantified with a statistic called foliage height diversity. Subsequently, similar patterns were found for many groups of animals in relation to \'cgetation .structure or other aspects of environmental hctcroiionciiy (Rechcr, 1969; Tonn and Magnuson, 1982; Anderson et ai, 1983; Gupta and Michael, 1992). However, we note with concern that human activities in the study area arc resulting in the degradaUon of several important biotopcsund the consequent homogenizalion of the landscape. Progressive siltation of fioodplain lakes, reclamaUon of marshes and such other ccotonal habitats for agriculture, conversion of prime agricultural land to brick kilns, and deforestation resulting in the conversion of dense forests on the hills-first to degraded forests, and then to scrub jungles and eventually W' ed-grown wavle'.'.iids are some of tiic lell-tale adverse impacts inflicted on the ecosys-
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terns in the study area. The general paucity of birds - only 60 species in about 50 sq. km. area - perhaps reflects this degraded state of the environment. A similar pattern was also observed by Gole (1987) in the deforested hills of Western Ghats where he recorded 160 species in a 121 sq. km. area. The removal of old mature trees is especially harmful, as it results in the absence of taxa like the hombills (family Bucerotidae) and the Shama {Copsychus malabaricusi family Muscicapidae), as has also been reported in the Western Ghats (Gole, 1987). Furthermore, as Table 1 reveals, the Redwinged Cuckoo {Clamator coromandus) and the Lesser Goldenbacke Wood-pecker (Dinopium benghalense) have been assigned a "Very rare" status in the study area, which means that their percentage frequency of occurrence is as low as 1 -9 per cent of the total. The decline in the populations if these two species, which are known to be associated with old, mature trees, are thus suggestive of considerable habitat destruction due to deforestation. This contentionis also supported by the observation that some other species inhabiting the hill forests have also been accorded a "rare" status in our survey (percentage frequency of occurrence 10-49 per cent). These include the Large Indian Parakeet {Psittacula eupatria), the Common Indian Nightjar (Caprimulgus asiaticus), and the Grey Shrike {Lanius excubitor). Further, though several other "rare" species like the Jungle Myna {Acridotheres fuscus fuscus), the Pied Rycatcher Shrike (Hemipus picatus capitalis), the Indian Wood Shrike {Tephrodamis pondicerianus), the Dark Grey Cuckoo Shrike {Coracina schistos), the Scarlet Minivet (Pericrocotus flammeus frateftuJus), the Assam Brown Hill Warbler {Prinia criniger catharia), the Yellow-bellied'Wren Warbler (P. flaviventris flaviventris), and the Black-headed Munia {Lonckura malacca stricapilla) were recorded from habitats like open forests, scmb jungles, lea gardens and the like, their breeding and nesting sites arc often located in dense forest. An interesting fact about certain common tree species in the hill forests of the study area such as Artocarpus and figs {Ficus spp.) is that they produce fruits having numerous small seeds. McKey (1975) hypothesized that such plants have their seeds dispersed by generalist frugivores. Figueiredo (1996) showed that in t!ie forests of Brazil, figs constituted important food sources for several bird species including thrushes, fiycatchers and parrots. Hence, the conservation of trees like Artocarpus and Ficus in the forests of Cachar may help attract several frugivore birds and increase the bird diversity therein. Yet another impact of deforestation is the resultant fragmentation and insularization of habitats that can no longer support a minimum viable population (MVP) required for the long-term survival of a species (Shaffer, 1987). The minimum area needed may very for different species, being some 50 acres for a pair of red-cockaded woodpeckers in U.S. forests (Reed et ai, 1988) Thus, considering all the above facts, the conservation of the dense hill forests in the study area is of prime concern. The other important bird habitats taht ought to be protected include the swamps, the marshlands with emergent trees, and the openwater areas in the Chatla floodplain, as they harbour several "rare" species like the Large Cormorant, the Black Bittern, the Bittern, the Indian Water Rail and the Marsh Spotted Babbler.
Another resident species whose numbers are fast declining in the study area is the Assam Black Partridge {FrancUnus francolinus melanonotus), found mostly in the tea
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gardens. The favoured habitatsiof this species include grassy hollws and bushes that offer cover, nesting site and food. Another subspecies of this genus, E f. asiae is found in the tea gardens of Kangra Valley, Himachal Pradesh, where it is known to roost on small thorny trees and feed upon insects, seeds and shoots of plants (KaUa et al., 1993) However, E f. melanonotus in the silcoorie-Dargakona area is becoming increasingly rzxe. due to indiscriminate hunting for its flesh. The other birds that are killed for this purpose include the Lesser Whistling Teal (a winter visitor to this area), the Common Teal, the egrets and the Pond Heron. Spread of awareness among the local populace could possibly ensure better protection for these taxa.
References
Ali, S.M. 1983. Some observations on the Ecology of the High Altitude Fauna in North Sikkim. Proc. Wkshp. High Alt. EnL & Wild]. Ecol. Zool. Surv. India ; 209-214.
Allaway, W.G. and A.E. Ashoford. 1984. Nutrient Input by Seabirds to the Forest on a Coral Island of the Great barrier Reef Mar. Ecol. Prog. Set. 19 : 297-298.
Anderson, B.W., R.D. Ohraart and J. Rice. 1983. Avian and Vegetation Community Structure and theii Seasonal Relationships in the Lower Colorado River Valley. Condor 85 : 392-405.
Bildstein, K.L., W. Post, J. Johnston and P. Frederick. 1990. Freshwater Wetlands, Rainfall and the Breeding Ecology of White Ibises in Coastal South Carolina. Wilson Bull. 102 : 84-98.
Bildstein, K.L., E. Blood andP.C. Frederick. 1992. The Relative Importance ofBiotic and Abiotic Vectors in Nutrient Processing in a South Carolina, U.S.A. Estuarine Ecosystem. Estuaries 15 : 147-157.
de Figueiredo, R.A. 1996. Vertebrates at Neotropical Fig Species in a Forest Fragment. Tropical Ecology 37: 139-141.
Gaston, A.J. and V.J. Zacharias. 1996. The Recent Distribution of Endemic and Disjunct Birds in Kerala State : Preliminary' Results of an Ongoing Sun'ey. J. Bomb. Nat. Hist. Soc. 93 ; 389-400.
Golovkin, A.N. 1967. The Effects of Colonial Seabirds on the Development of Phytoplankton. Oceanology 7:521-529.
Golovkin, A.N. and G.P. Garkavaya. 1975. Fertilization of the Waters of the Murmansk Coast by Bird Excreta near Various Types of Colonies. Sov. J. Mar. Biol. 15 : 345-351.
Gole, R 1987. Birds of Deforested Hills. J. Bomb. Nat. Hist. Soc. 84 : 275-290. Gupta, A. and R.G. Michael. 1992. Diversity, Distribtaion and Seasonal Abundance of Ephem"roptera in Streams of Meghalaya State, India. Hydrobiologia 228 : 131-139. Hafncr, H. and R. Briiton. 1983. Changes of Foraging Sites by Little Egrets (Egrelia garzetla L.) \n Relation to Food Supply.
Kalia, H.R. and B.K. Kaul. 1976. Dwindling Wild Life in the Changing Eco.^'Stem of the Northwest Himalaya with Special Reference to Rare Birds and Mammals. Proc. Intemat. Hill Land Symposium, Morgantown: 568-573.
Kalia, H.R., B.K. Kaul and S.F. Hamced. 1983. Studies on the Ecology and Zoogeography of Northwest Himalayan Partridges with Some Experiments on the Artificial Propagation ofAlectorics chukar and Coturnix cotumix. Proc. Wkshp. High All. F.nl. & Wildl. licol. Zool. Surv.
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India: 247-257.
Khacher, L.KL 1996. The Birds of Gujarat - A Salitn Ali Centenary Year overview. J. Bomb. Nat. Hist. Soc. 9 3 : 331-373.
MacArthur, R.H., and J. MacArOiur. 1961. On Bird Species Diversity. Ecology 42: 594-598. McKey, D. 1975. The Ecology of Co-evolved Seed Dispersal Systems, pp. 159-191, In : L.E. Gilbert and P.H. Haven (eds.), Coevolution of Animals and Plants. University of Texas Press, Austin.
Morales, G., and J. Pacheco. 1986. Effects of Diking a Venezuelan Savanna on Avian Habitat, Species Diversity, Energy Flow, and Mineral Flow through Wading Birds. Colon. Waterbirds 9 : 236-242.
Recher, H.F. 1969. Bird Species Diversity and Habitat Diversity in Australia and North America. American Naturalist 103 : 75-80.
Reed, J.M., RD. Doerr and J.R. Walters. 1988. Minimum Viable Population Size of the Red-Cochaded Woodpecker. J. Wildl. Mgmt. 52 : 385-391.
Shaffer, M. 1987. Minimum Viable Populations: Coping with Uncertainty, pp. 69-86, In : M.E. Soule (ed.), Viable Populations for Conservatioa Cambridge University Press, Cambridge.
Subramanya, S., and J.N. Prasad. 1996. Yellow throated Bulbuls at Horsley Hills. J. Bomb. Nat. Hist. Soc. 93 ; 55-58.
Tonn, W.W., and J.J. Magnuson. 1982. Patterns in the Species Composition and Richness of Fish Assemblages in Northern Wisconsin Lakes. Ecology 63 : 1149-1166.
Vyas, S. 1996. Checklist of the Birds of the Delhi Region: An Update. J. Bomb. Nat. Hist. Soc. 93 : 219-237.
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Journal of Assam Univosity O Vol3(l) (1998)
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Introduction
Heavy metals, especially mercury, cadmium, lead, chromium,
selenium, boron, manganese, copper, zinc, and the like, have attracted the
attention of scientists since the last few decades t)ecause of many pollution
Incidents resulting from their release into the environment, as well as l)ecause
of their high toxicity (Borg ef a/., 1969; Fujiki et a/., 1972; Bakir et al.. 1973;
Fr(t>erg etal., 1974; Bryan, 1979). While some of these metals like copper, zinc,
iron, manganese and some others are needed in extremely trace amounts by
many plants and animals for their metabolic activities, any increase in the
concentrations of these elements beyond certain threshold levels can prove
disastrous. The increased inputs of toxic metals into the environment mostly
Mi
Eggshells as monitors of heavy metal pollution 227
result from human activities (Lantzy and Mackenzie, 1979), and these
xenobiotic substances are known to have deleterious effects not only on
wildlife, but also on human health (Furness, 1993). The increasing concem
about the long-term effects of the metals on the environment (Hutchinson and
Meema, 1987) has led to a search for effective ways of monitoring their nature
and extent of contamination, and in this context biological nronitoring has been
shown to be a satisfactory way to quantify heavy metal abundance and
bioavailability (Phillips, 1980; Schubert, 1985; Thompson, 1990). This is
because metals have been found to accumulate in organisms to levels much
higher than found in water, air, soil or sedimente, and are consequently much
easier to measure than in the physical environment. Various species of
macroinvertebrates, especially bivalve nrallusks, have been shown to be
excellent biomonitors of trace metals in both freshwater and marine systems
(Phillips, 1980). Fish has also been used, albeit less frequentiy, for monitoring
of frace metals (Leah et al., 1991). It is also thought that the recent declines in
the populations of marine mammals may be due to ttieir increasing metal
burdens (Marcovecchio e al., 1990; Law et al., 1991). Birds also offer a
number of advantages as possible biomonitors of ti"ace metals. This is because
the ecology of most bird species is fairty well known. Furthermore, birds feed at
the higher frophic levels of ecosystems and ttierefore can provide information
on the extent of contamination in the entire food chain (Furness, 1993).
Seabirds have been shown to be efficient monitors of frace metals (Brothers
and Brown, 1987; Walsh, 1990), although It is always not necessary that high
Eggshells as monitors of heavy metal pollution 228
metal levels in birds reflect metal pollution of the environment (Murton et ai,
1978; Muirliead and Fumess, 1988). Among ttie different tissues, liver, kidney,
feathers and eggs have been widely used for monitoring metal levels in birds
(Hutton, 1981; Thompson and Fumess, 1989; Thompson etai, 1991; Lock et
ai, 1992). The avian egg has been used in several studies (Parslow and
Jefferies, 1977; Banrett ef a/., 1985; Ohiendorf and Harrison, 1986; Burger and
Gochfeld, 1988d; Becker, 1989), and has been shown to have several
advantages over internal tissues, as they have a highly consistent composition
unlike sevesral other tissues like liver. Besides, sampling eggs takes less time,
they are easy to handle, can be collected with litfle interference, and their
renraval places less pressure on a population than that of adults or juveniles,
especially if only one egg is removed from a given clutch (Fumess, 1993). In
conti ast, analysis of internal tissues requires killing of a large number of birds
which is fiighly undesirable for practical as well as ethical reasons. Most
importantiy, eggs have been shown to reflect metal uptake from local foraging
more closely than tissues from adult birds (Parslow and Jefferies, 1977; Barrett
et a/., 1985). They are now regarded as particularly useful in monitoring
mercury and selenium levels in the environment although their value in
assessing pollution by other heavy metals have not been clearly documented
till date. It has been suggested that eggshells could be potentially useful
materials for monitoring certain heavy metals such as cadmium and lead
(Furness, 1993). The present study, therefore, attempts to explore the
possibilities of using the eggshells of different Ardeidae species in biological
Eggshells as monitors of hemy metal pollution 229
monitoring of heavy metal pollution of the environments. The metals analyzed
included chromium, cadmium and lead. The objectives of the present
investigation were to find out the nature and extent of metal accumulation in the
eggshells of six Ardeid species, viz., Bubulcus, ibis, Egretta garzetta, Meola
gray//, Ixobrychus miriutus, I. cinnamomeus and Bofaums stellahs; to explore
the suitability of using the eggshells of ttiese species in monitoring of
chromium, cadmium and lead pollution of the environment; and to find out the
pattern of metal deposition in and around the different heronries of herons and
egrets, and the nesting sites of bitterns wherefi'om the eggshells were
collected.
Review of Literature
Toxicity from heavy metals such as mercury, cadmium, lead,
chromium and others have prompted many investigations into their monitoring
and management. Most of these metals have no biological function, and their
enti7 into the environment largely results from anthropogenic activities (Borg et
manganese-0.48 (0.17-1.1), strontium-1.90 (1.3-2.9), and zinc-11.5 (7.2-21)
(Mora, 1996b). In a recent study, selenium and boron were found to be
Eggshells as monitors of heavy metal pollution 233
toxicants of concern as shown by ttieir elevated levels in the eggs of the
endangered southwestern willow flycatcher collected from several breeding
areas in Arizona and California, U.S.A (King et al., 2002). Thus, eggs are now
regarded as potentially useful materials for monitoring mercury, selenium and
boron, while eggshells could be successfully used for some other metals like
cadmium and lead (Fumess, 1993).
Materials and Methods
Eggshells of Bubulcus ibis, Egretta garzetta and Ardeola grayii were
collected from heronries on bamboo groves in Salchapra and Dwarbond in
Cachar district and Lakshmisahar area of Hailakandi town in Hailakandi district
of Barak Valley, Assam. Eggshells of bitterns were collected from nests inside
wetlands in Sonai (3 sites) and Jirighat in Cachar district Matijuri in Hailakandi
distict and Sarisha (2 sites) in Karimganj district. Three replicate samples were
collected for each species from each site. These were scraped with a PVC
scalpel and washed with distilled water to remove any attached membranes
and exfraneous materials. They were then weighed and digested to dryness in
10 ml concentrated HNO3. The residues were suspended in 20 ml 10 % HNO3
(Mwangi and Alikhan, 1993; Gupta. 1996, 1998a, 1998b). Analysis for
chromium, cadmium and lead contents were done in a Perkin-Elmer 2380
Flame Atomic Absorption Spectrophotometer. The readings were checked with
< i
Eggshells as monitors ofhemy metalpollulion 234
those for standard solutions, and contamination errors minimized by using
blanks, acid-washed glassware, analytical grade reagents and double-distilled
deionized water. The detection limits for Cr, Cd and Pb were 0.5, 4.0 and 10.0
|ig \-\ respectively.
Results
Table 4.1 depicts the concentrations (jig g^ dry weight) of chromium,
cadmium and lead in the eggshells of Bubulcus ibis, Egretta garzetta, Ardeola
grayii, Ixobrychus minutus, /. cinnamomeus and Botaurus stellahs from
heronries in 10 different sites in Barak Valley. The chromium levels in the
samples ranged between cadmium levels in all the samples ranged between
0.16-0.32 |ig g ^ those of cadmium between 0.050-0.082 jag g-\ and those of
lead between 0.557-1.064 ^g g\ The highest concentration of chromium (0.32
lig g') was recorded in eggshells of /. minutus from Sonai 3 site, while the
lowest (0.15 |ig g was in those of 6. sfe//ans from Jirighat. The highest level
of cadmium, on the other hand, was found in eggshells of A. grayii
(0.082 lag g^) collected from heronries in Salchapra, Cachar district, while the
lowest concentrations of this metal were in those of 6. ibis from heronries in
Lakshmisahar, Hailakandi district, and in those of B. stellahs collected from
nests in Jirighat, Cachar district (0.050 i g g- in both samples). The highest
lead concentration was recorded in eggshells of iA. grayii from heronries in
Salchapra, Cachar district, while the lowest concentration was from those of B.
M±
Eggshells as monitors of heavy metal polh4lion 235
ibis from Lakshmisahar, Hailakandi district (1.064 and 0.557 ^g g^,
respectively). Table 4.2 depicts the mean concentrations of the three metals in
the eggshells of the different Ardeidae species. Highest chromium
concentrations were recorded in those of A. grayii and /. minutus, while the
highest cadmium and lead levels were recorded in those of A. grayii.
Discussion
As revealed in Table 4.1, the metal content in the eggshells of the
different species of Ardeidae showed some variations among sites as well as
among species. When compared with the metal concentrations obtained in
allied species in existing studies conducted in other parts of the worid, the
cadmium contents recorded in the eggshells are far below any adverse effect
level. For instance, the eggs of the Great Blue Heron, Ardea herodias were
found to contain 0.22 |4,g g- cadmium (Blus et al., 1985). On the other hand,
chromium levels recorded in the present study (0.16-0.32 pg g- ) were more or
less comparable to those recorded in A. herodias. In 1980, a total of 40 heron
eggs were collected from four rookeries in Tennessee Valley, U.S.A. Chromium
was detected in all butone egg with means of 0.23.0.18, 0.16, and 0.18 pg g-
', respectively (Fleming et a!., 1984). In yet another study (Mora, 1996), a
median chromium concentration of 0.29 ug g ' with a range of 0.09-11 ug g-'
Eggshells as monitors of heavy metal pollution 236
was detected in the Great Blue Heron. The present study further reveals that
among the eggshells of the 6 Ardeid species collected from 13 sites in Barak
Valley, chromium levels were relatively higher (0.28-0.32 |ig g- ) in those of E.
garzetta and A gray/; from Salchapra, Cachar district /. m/nuftys from Sonai 2
and Sonai 3, Cachar district 6. stellaris from Matijuri, Hailakandi district and /.
cinnamomeus from Sarisha 1, Karimganj district Thus the eggshells of £.
garzetta, A. grayii, I. minutus and /. cinnamomeus could be further explored for
their possible utility in monitoring chromium levels in the ambient environment
and especially in the foraging grounds. Relatively high lead levels were
recorded in the eggshells of E garzetta, A. grayii, and /. cinnamomeus (0.912,
1.064 and 0.912 ^g g-^ respectively) firom the heronries and nesting sites of
Salchapra and Sarisha 1 (Table 4.1). Lead levels are considered high and
capable of producing adverse effects beyond the 1 |j.g g- threshold (Elliott et
al., 1989). Hence the lead levels recorded in the three species may be said to
reflect lead contamination of foraging grounds in certain areas of Barak Valley.
It may be noted that lead levels were around 0.8 |ig g^ in the eggshell samples
of /. minutus and B. stellaris collected from several nesting sites in Barak
Valley (Table 4.1). This perhaps indicates that lead is one of the major metal
contaminants of this area. The most likely source of lead in this region are
automobiles that consume unleaded petrol which was in use till recently in
North East India. Gupta (1996) also found lead to be one of the major metal
contaminants in a stream ecosystem in Shillong, Meghalaya. The Ardeids are
likely to have accumulated lead as well as chromium from their foraging
Eggshells as monitors of heavy metal pollution 237
grounds in the wetlands near their nesting sites. Wetland sediments in Barak
Valley were shown to contain significantly higher levels of several heavy metals
such as cadmium, chromium, iron, manganese, nickel, lead and zinc as
compared to those from the river. Furthermore, the different tissues of a snail,
Angulyagra oxytropis were also found to accumulate these metals at
significantly higher levels (Gupta, 1998b). The egrets, herons and bitterns
feeding in these wetlands appear to have accumulated the metals through food
chain transfer, which in turn, got mobilized in their eggshells. However, no
concrete evidence for food chain concentration or biomagnification could be
discerned in the present study. Among the different sites from which the
eggshells were collected, those from the heronries at Salchapra, and nesting
sites at Sonai 2 and 3 as well as Sarisha 1 were found to exhibit higher metal
contents. This could have been due to their proximity to busy National
highways with heavy fraffic that resulted in the contamination of nearby
wetiands with chromium and lead. In confrast eggshells did not show any net
bioaccumulation of cadmium in the present study, although they could be of
potential use in the biomonitoring of chromium and lead. It may be interesting to
continue the monitoring of lead levels in the eggshells to discem any decline in
the levels of this metal, as non-leaded peti"ol is now being used in this region.
Eggshells as monitors of heavy metal pollution 238
Table 4.1. Conceiitrations (ng g"') of Chromium, Cadmium and Lead (X ±
S.D.) in eggshells of Ardeidae collected from diffCTent nesting sites in Barak
Valley, Assam, India.
Species
Bubulcus ibis
Bubulcus ibis
Egretta garzetta
Egretta garzetta
Ardeola grayii
Ardeola grayii
Ixobrychus ndnutus
Ixobrychus minutus
Ixobrychus minutus
Botaurus stellaris
Botaurus stellaris
Ixobrychus
cintiamomeus
Ixobrychus
cinnamomevs
Location
Salchapra
Lakshmisahar
Salchapra
Dwarbwid
Dwarbond
Salcha]XB
Sonai 1
S<»ai2
S«iai3
Jiri^t Matijuri
Sarisha 1
Sarisha2
Ciiromittin
0.24+0.08
0.20+ 0.06
0.28+0.09
0.20+0.06
0.24+ 0.08
0.28+ 0.09
0.24+ 0.08
0.28+ 0.09
0.32+0.10
0.16+0.05
0.28+0.09
0.28+0.09
0.21+0.04
Cadmiain
0.069+0.008
0.050+0.006
0.064+0.007
0.059+0.006
0.073+0.008
0.082+0.009
0.059+0.006
0.078+0.008
0.078+0.008
0.050+0.006
0.055+0.006
0.069+0.008
0.069+0.008
Lead
0.608+0.028
0.557+0.026
0.912+0.042
0.709t 0.033
0.760+0.035
1.064+0.049
0.811+0.038
0.811+0.038
0.811+0.038
0.709+ 0.033
0.861+0.040
0.912+0.042
0.760+0.035
Eggshells as monitors of heavy metal pollution 239
Table 4.2. Mean concentrations (ng g"') of Chromium, Cadmium and Lead in
the eggshells of the different species of Ardeidae from Barak Valley, Assam,
India.
Species
Bubulcus ibis
Egretta garzetta
Ardeola grayii
Ixobrychus minutus
I. cinnamomeus
Botaurus stellaris
Chromium
0.22
0.24
0.26
0.26
0.245
0.22
Cadmium
0.06
0.062
0.078
0.069
0.069
0.053
Lead
0.58
0.81
0.91
0.81
0.84
0.79
Conclusions
Conclusions The present investigation on tfie avifauna of Barak Valley, Assam,
Nortti Eiast India, with special reference to family Ardeidae, revealed the
presence of 239 species of birds in the forests, wetlands, tea gardens, urban
and rural areas, and other habitats of this area. Of these 239 species, as many
as 27 (11.3 %) are considered threatened at a global level. Additionally another
78 species are now rarely encountered in Barak Valley. Thus about 38 % of the
bird diversity in this area may be considered as threatened to varying degrees.
Factors such as degradation of bird-rich habitats like wetlands and dense,
primary forests, as well as hunting and trapping are instrumental in bringing
about thi.s decline in bird diversity. Three 'Important Bird Areas' (IBAs), Viz., the
Shon Beel, a large floodplain wetland in Karimganj district, the Katakhal and
Inner Line Reserve Forests in Hailakandi and partly Cachar districts, and the
Conclusions 241
Barail Reserve Forest in hilly tracts of Cachar bordering North Cachar Hills
district have been recognized. Based on the avifaunal diversity recorded in the
the present investigation, recognition of two additional IBAs is suggested, viz.,
the Bauwaa Beel, a wetland in Hailakandi district, and the Barak Reserve
Forest in the eastern part of Cachar adjoining Manipur. Adoption of suitable
protective and ameliorative measures including habitat restoration and
reduction of hunting pressure, especially in the IBAs are likely to go a long way
towards conserving avifaunal diversity in Barak Valley. A special emphasis
ought to be given to the maintenance of structural complexity of vegetation in
the forests that in turn maintains a high foliage height diversity. However, the
forests in Barak Valley are rapidly becoming species poor and homogenous,
thereby affecting the thriving of birds in such habitats. The forests of Barak
Valley are naturally rich in tree species like Mocarpus chaplasha and several
species of figs {Ficus spp.). These trees produce firuits with numerous small
seeds that are dispersed by generalist frugivores. Such fruits constitute
Important food resources for forest birds like thrushes,' flycatchers and pan^ots.
Hence, the conservation of such trees can help attract these birds and improve
bird diversity in the forests of Barak Valley. It may be noted here that several
species of thrushes and flycatchers in the forests of Barak Valley have been
found to of rare occun-ence. Habitat heterogeneity is drastically declining in
wetland areas as well, with clearing of swamp trees, draining of marshes, and
the resultant creation of turbid, vegetation poor ecosystems. Removal of
nesting trees such as Bombax ceiba, other wetland trees like Barringtonia
l£ii
Conclusions 242
acutangula and Lagerstroemia flosreginae, is also creating unfavourable
conditions for many wetiand species. Extension of legal protection under the
Indian Wildlife Protection Act (IWPA) to additional species of birds is also
necessary. Several species found in Barak Valley (and in other areas of
Assam) that need to be brought under the protective umbrella of Schedule I or
II of IWPA include the Baer's Pochard {Aythya baen), the Black-necked Stork
{Ephippiorhynchus asiaticus), the Greater Spotted Eagle (Aquila clanga), and
the Bunnese Sarus (Grus grus sharpii). Among the members of the Ardeidae,
the Littie Green Heron {Butorides striatus) and the Grey Heron (Ardea cinerea)
deserves immediate protective measures in Barak Valley.
The food habits and feeding propensities of six species of Ardeidae
reveal that wetiand ecosystems like marshes and swamps, small sti'eams and
canals, inundated paddy fields, and other low-lying floodplain areas constitute
important foraging grounds for these species. As already mentioned the
conservation of these resource-rich areas could be insb-umental in providing
adequate supply of food not only to the egrets, herons and bitterns, but also to
a host of other wetiand species of birds. The six species of Ardeidae that were
studied for their food habits and feeding behaviour, revealed a certain degree of
both spatial as well as temporal ti'ophic niche partitioning. For instance,
Bubulcus ibis exploited the paddy field areas more as compared to the other
species. They also obtained their food such as ticks from the grazing animals
with which they were found to be associated. During the dry season, they were
also found to forage in dry paddy fileds, small hillocks and high ground habitats.
Mi
Conclusions 243
The pond heron, along with cattle egret utilized the inundated paddy fields the
most However, the herons and egrets exhibited differences in timings of peak
feeding, l-or instance, the pond heron fed most intensively during eariy morning
and afternoon, the cattle egret during forenoon, and the litUe egret during
afternoon. The bitterns, on the other hand, foraged deep in marshy areas, with
some degree of temporal separation in pesk feeding activities. These
mechanisms appear to allow them to coexist in similar habitats.
Bamboo groves were found to be a very important habitat for nesting
by the two egret species and the pond heron. Nests of A grayii occupied the
highest portions of the bamboo culms between 5-5.5 m, those of 6. ibis
intermediate at 4-4.5 m, and the lowest level was occupied by e. garzetta at
3.5-4 m. They shared the bamboo grove habitat with the little cormorant P.
niger, which occupied the highest level. A redeeming feature observed during
the present study was the protection offered by several communities such as
the Bisnupriyas and the Meeteis, the tea garden labourers and Bengali Hindus
to the nesting sites of these species, as they are believed to usher in prosperity
for the villagers. This greatiy influenced nesting site selection by the birds,
along with the availability of suitable foraging sites in close proximity to the
heronries. Needless to say, continued availability and conservation of bamboo
groves in the countiyside of Barak Valley appears to be an important factor in
the conservation of these species of Ardelds. The Hindustan Paper Corporation
(HPC) has recentiy mooted a proposal to utilize wastelands in rural areas for
bamboo plantations that could later be periodically harvested to meet the
Mi
Conclusions 244
demands of the paper mill at Panchgram, Hailakandi district By properly
adjusting the harvesting schedule, and earmarking certain groves as protected,
this plantation programme could perhaps be profitably utilized for improved
nesting site availability for cormorants, egrets and herons.
The analysis of chromium, cadmium and lead in the eggshells of six
species of Ardeidae revealed that lead, and to some extent chromium were
accumulated in the eggshells, while cadmium levels were very low and much
below the adverse effect level. Lead was found to be the most significant nrretal
contaminant among the three metals analyzed. Thus the present study reveals
that eggshells of Ardeids, and possibly other bird species as well, could be
profitably utilized for the monitoring of this metal in the ambient environment. It
may be worthwhile to watch for any decline in lead levels with the marketing of
non-leaded petrol in this area in the recent years.
Ik
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