First detailed survey of waterbirds in Tirunelveli and Tuticorin districts, Tamil Nadu, India
K. Abhisheka 1, J. Patrick David 2, M.B. Prashanth 3, K.S. Seshadri 4 & T. Ganesh 5
1,2,3,4,5 Ashoka Trust for Research in Ecology and the Environment, Royal Enclave, Srirampura, Jakkur post, Bengaluru, Karnataka 560064, India
Present address: 2 Careearth Trust, 8/15, 2nd Main Road, Thillaiganga Nagar, Chennai, Tamil Nadu 600061, India
Present address: 4 Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543
1 firstname.lastname@example.org (corresponding author), 2 email@example.com, 3 firstname.lastname@example.org,
4 email@example.com, 5 firstname.lastname@example.org
Abstract: The semi-arid districts of Tirunelveli and Tuticorin in the southern Indian state of Tamil Nadu consist of numerous wetlands in the form of irrigation tanks, interconnected by an ancient network of canals, and fed by the rivers originating from the Western Ghats. While these irrigation tanks have socio-economic and cultural significance, very little is known of their ecological importance. These tanks have the potential to harbor good populations of resident and wintering waterbirds but no studies have been done to confirm this. A survey was carried out in 230 irrigation tanks of various sizes in the two districts from November 2008 to January 2011. A total of 83 waterbird species were recorded. Indian Pond Heron Ardeola grayii occurred in most of the surveyed tanks. Large concentrations of wintering waterfowl such as Eurasian Wigeon Anas penelope, Northern Pintail Anas acuta, Garganey Anas querquedula were recorded in tanks closer to the coast. Based on our survey, six sites with large waterbird concentrations have been identified, one of which is Vagaikulam, an active heronry currently under threat from tree felling. These sites along with associated wetlands are important for the long term conservation of waterbirds in the region.
Keywords: Heronry, irrigation tanks, long term monitoring, waterfowl.
Wetlands, both natural and artificial, support a high diversity of resident and migrant waterbirds (Amezaga et al. 2002). Though there are numerous such habitats for birds across India, very few have been systematically surveyed to understand their importance for birds. This is especially true for many small ones that are in an agricultural landscape often fed by man-made irrigation networks and collectively supporting large populations of waterbirds. As part of conservation efforts, isolated wetlands or heronries in the agricultural areas get listed as important bird areas (IBA). Though such efforts are important, they provide inadequate coverage, and are of limited value unless the surrounding habitat matrix such as swamps, canals, wet agricultural areas - which effectively sustain a good population of birds are included in the conservation plans (Elphick et al. 2010; Sundar 2011). It, therefore becomes imperative that a landscape approach is used to establish the importance of wetlands for waterbirds.
The districts of Tirunelveli and Tuticorin in the semi-arid landscape of southern Tamil Nadu have many man-made, small- to large-sized, irrigation tanks (henceforth called tanks). These inland tanks were built a few centuries ago and are interconnected by canals that bring water from the rivers originating in the Western Ghats (Vaidyanathan 2001). These rivers and associated tanks support a rich social and cultural heritage and economically support agriculture that is the main source of livelihood for the people in these districts.
The tanks in these two districts are known to support large populations of the Near Threatened Spot-billed Pelican Pelecanus philippensis, and Painted Stork Mycteria leucocephala (Kannan & Manakandan 2005; Subramanya 2005). They also provide suitable habitat for the Greater Flamingo Phoenicopterus roseus (Sathan & Pandi 2009) and sustain a variety of migrant water birds during the winter. Not surprisingly, the area has also been known to sustain heronries like Koonthankulam, Gangaikondan, Moondradaippu, Tirupudaimarathur, Vijayanarayanam, Karungulam and Ariyakulam (Krishnan 1978; Nagulu & Rao 1983; Subramanya 1996). However, past reports were based on small-scale surveys and are outdated as some of the aforementioned heronries do not exist today.
Though there are studies on birds in the two districts, most have been restricted to forest birds in the neighboring Kalakad-Mundanthurai Tiger Reserve (KMTR) (Johnsingh & Joshua 1989, 1994; Johnsingh 2001; Raman & Sukumar 2002), whereas in the semi-arid plains, focus has been on Koonthankulam and other heronries (Rhenius 1907; Webb-Peploe 1945; Wilkinson 1961; Subramanya 2005). While Koonthankulam is notified as an IBA, scant attention is given to the other tanks in this network which potentially harbor a high diversity of resident and migratory waterbirds. There are over 3000 tanks here and some of them are large (over 1700 acres). There is a need to identify tanks important for resident and migrant waterbirds, and prioritize them for conservation. Moreover, the tanks and agricultural fields in these two districts along with the neighbouring Kanyakumari District are located towards the southern tip of the Indian peninsula and therefore provide critical wintering habitats for many migrant species. Several of these tanks are, however, threatened by various anthropogenic factors (Abhisheka et al. 2012). In this context, robust baseline information on waterbird diversity and populations can provide a starting point for future monitoring, conservation planning and developing pertinent management interventions.
In this paper we provide the results of a survey of 230 tanks to document the diversity and abundance of waterbirds in Tirunelveli and Tuticorin districts of Tamil Nadu. We identify key sites that harbor large populations of resident and migrant waterbirds that will be useful for waterbird conservation.
Study area and Methods
Located in the southern most part of India, the two districts, Tirunelveli (8008Õ–9023ÕN & 77009Õ–77054ÕE) and Tuticorin (8049ÕN & 7808ÕE) are encompassed by the Western Ghats on the west and the Bay of Bengal on the east. This region is known as the rice bowl of southern Tamil Nadu, made possible by the many rivers that originate in the Agasthyamalai Hills, and also as a biosphere reserve and a proposed world heritage site (Rehman & Shrivastava 2012). The numerous tanks (~3000) that lie in the semi arid plains of these two districts are fed by seven perennial rivers viz., Thamiraparani and its tributaries: Manimuthar, Pachaiyar, Kodumudiyar, Gadananathi, Ramanathi and Nambiar which form the lifeline of about five million people living in the immediate landscape (Gazetteer 2002). The Thamiraparani is a major river, which plays a vital role by providing water for irrigation and sustaining the people living in its basin. The river originates from the catchments of the Periya Pothigai hills in the Agasthyamalai region of the Western Ghats and traverses through the two districts before joining the Gulf of Mannar in the Bay of Bengal at Punnaikayal.
The river-canal-tank network in the semiarid landscape sustains extensive paddy agriculture in the region. The old trees and plantations in the region support heronries while the Borassus flabellifer palm traditionally planted around the tanks offers roosting sites for numerous resident birds. A survey of 230 small to large tanks (10–1705 acres) based on size and logistics was carried out in three phases in the districts of Tirunelveli and Tuticorin from November 2008 to January 2011 (Appendix 1). A very large proportion (>50%) of small tanks close to the forests were surveyed during this period. Surveys were carried out between September to February for two reasons: one, it included the wintering period for migrant waterfowl and second, the September to October period is a dry period with very few tanks having water. This allowed us to identify critical tanks where waterbirds could be found during water shortage in the larger landscape. Though this is biased against migratory birds these water bodies can be critical for resident species which experience seasonal water shortages on a regular basis. Indian Remote Sensing Satellite, Google Earth images, maps from the Survey of India and information from Public Works Department, Government of Tamil Nadu were used to locate wetlands for the survey. These sources of information were also used to determine the extent of each tank in acres.
During the first phase, 177 tanks were surveyed along the foothills of KMTR spread over a distance of 65km from November 2008 to September 2010. Nearly all tanks close to the rivers Gadananathi, Thamiraparani, Manimuthar, Pachaiyar and Nambiar were surveyed. In the second phase, all the tanks on the banks of the Thamiraparani river in both districts were surveyed (n=22) in the month of September 2010. In the third phase, a mid-winter waterfowl census was conducted across the two districts in Jan 2011 (n=42). Eleven tanks surveyed in the earlier two phases were part of the 42 tanks. Only large tanks were chosen for the mid-winter survey as many volunteers were available for the survey and it could be done in 2–3 days (Fig. 1). All large tanks in the dry areas of the districts away from the river basin were also surveyed. In total, 230 individual tanks were covered during the two phases and the mid-winter waterfowl census.
In each of the tanks, the number of bird species and the number of individuals were recorded. The total number of birds was enumerated by walking along the periphery of the tanks in the mornings from 06:30–09:30 hr or in the evenings from 16:00–18:00 hr as this time period was found to be most appropriate during pilot surveys. Large tanks were divided into blocks to simplify counting and sometimes were surveyed beyond 09:30 hr due to their size. Waterbirds were counted from a few vantage points, as gaining access to all sides of the tank was difficult in a few cases. A minimum of two members for small to medium tanks and four members, split into two groups, for large tanks, counted the birds. All members of the team were experienced bird watchers and familiar with water bird counting. The mid-winter waterfowl census was carried out by over 30 people split into two or four groups, with each group having at least one experienced birdwatcher. Often, in large wetlands complete counts were biased by the presence of vegetation and large distance from bird to the shore and may have led to underestimates of counts but not so in smaller wetlands. We also recognize that abundance estimates can be biased by observer, year, day of count, potential double counting, and other factors, but were unable to account for these in our study.
All surveys were carried out using binoculars (8X40, 10X50) or using spotting scopes (10X100). Geographic coordinates (latitude and longitude) were obtained at one arbitrary point for each tank using a Garmin¨ hand-held global positioning system.
Tanks critical for water bird conservation was decided based on the presence of heronry, high species richness, greater abundance of waterbirds, habitat diversity present in the wetland, and availability of water during the dry seasons spanning from March to October. Local villagers around the tanks were consulted about the tankÕs history, source of water and the availability of water in it. Grouping of birds, classification, common and latin names were based on international ornithological committee (IOC) World Bird Names (Gill & Donsker 2012). SpeciesÕ global status was ascertained using the IUCN classification (IUCN 2010).
Results and Discussion
A total of 83 species of waterbirds were recorded in the 230 tanks surveyed (Appendix 2). Of the 83 species about 41% were migrants, 26% local migrants and 33% residents. More than 13,164 individuals and 69 species were recorded during the phase one survey of 177 small tanks in the foothills of KMTR. In phase two 20,406 individuals of 58 species were recorded in 22 tanks and finally 32,379 birds of 71 species were recorded in 42 tanks during the mid winter waterbird census. These variations were mostly due to the size of tanks, since tanks surveyed in phase one were smaller than in other phases.
Indian Pond Heron Ardeola grayii was the most common species and occurred in 76% of the 230 tanks surveyed, followed by Little Egret Egretta garzetta (75%) and Little Cormorant Phalocrocorax niger (71%). A few species were recorded in only one tank, and some examples of these are Black-capped Kingfisher Halcyon pileata, Common Tern Sterna hirundo, Great Thick-Knee Esacus recurvirostri, Lesser Sand Plover Charadrius mongolus, Little Stint Calidris minuta, Oriental Pratincole Glareola maldivarum, Ruff Philomachus pugnax, Small Pratincole Glareola lactea, Watercock Gallicrex cinerea and Whimbrel Numenius phaeopus. Four bird species in the Near Threatened category; Black-headed Ibis Threskiornis melanocephalus, Oriental Darter Anhinga melanogaster, Painted Stork and Spot-billed Pelican were recorded in large numbers in these tanks. Some species like the Black-capped Kingfisher was restricted to the foothills while Ruff, Whimbrel, Eurasian Wigeon Anas penelope and Lesser Sand Plover were seen more often in tanks closer to the coast.
The Common Pochard Aythya ferina, Eurasian Wigeon, Great Thick-Knee, Pied Avocet Recurvirostra avosetta, Ruff, Whimbrel and Watercock were sighted for the first time during the survey. Though all of these species are expected to occur in the region (Grimmett et al. 1999), there have been no prior reports from the focal districts.
Among the tanks surveyed, six were prioritized for conservation attention (Table 1). Three tanks were chosen on the basis of having waterbird abundance greater than 1% population threshold as per Ramsar criteria (Table 2). The other three were chosen based on the high abundance and species richness of birds. While we highlight only six tanks, all the tanks have a great potential to support large waterbird congregations, and they are also existing and potential nesting/roosting sites. The six tanks are represented in Fig. 1 along with all the large tanks.
Vagaikulam (81 acres) situated at Nanalkulam near Alwarkurchi in Tirunelveli district was found to support 45 species. It has no other heronries in a radius of 65 km and is one of the largest heronries in the district of Tirunelveli after the Koonthankulam bird sanctuary. The tank comprises of semi submerged Acacia nilotica trees and is an important nesting and roosting site for several non-migratory species of birds like Black-crowned Night Heron Nycticorax nycticorax, Black-headed Ibis, Little Cormorant, Indian Cormorant Phalacrocorax fuscicollis, Great Cormorant Phalacrocorax carbo, Little Egret, Indian Pond Heron, Little Grebe Tachybaptus ruficollis, Common Moorhen Gallinula chloropus, Pheasant-tailed Jacana Hydrophasianus chirurgus and Bronze-winged Jacana Metopidius indicus. The tank also supports roosting populations of Glossy Ibis Plegadis falcinellus, Spot-billed Pelican and ducks like Cotton Pygmy-Goose Nettapus coromandelianus, Garganey Anas querquedula, Northern Pintail Anas acuta, and Lesser Whistling-Duck Dendrocygna javanica. The water in the tank is seasonal and the heronry is active from November to March. The heronry is under threat from the felling of Acacia nilotica trees planted by the forest department.
Pirancheri Periyakulam (94 acres) situated on the Tirunelveli-Ambasamudram main road supported 45 species during this survey. The floating vegetation in the tank along with grass and reeds makes this a suitable habitat for dabbling as well as wading birds. The vegetation provides nesting habitat for Moorhens, Jacanas and Herons. Water from Thamiraparani feeds this tank and it is perennial. Weed infestation and dumping of garbage is posing significant threat to this tank. Expansion of a road in future is another possible threat to the tank.
Vattakulam (125 acres) situated on the Cheranmadevi–Nagercoil Road is a large tank close to Tirukurangudi Village at the southern end of Kalakad Mundanthurai Tiger Reserve. During the survey 33 species were recorded. Pelicans, storks, and egrets congregate here in large numbers to feed on the fish in the shallow water when the tank starts to dry out. The tank shore line is used by several small waders like the Common Sandpiper Actitis hypoleucos, Black-winged Stilt Himantopus himantopus, Little Ringed Plover Charadrius dubius and Marsh Sandpiper Tringa stagnatilis. The tank is seasonal and fed by the Nambiar River. We did not document any major threat to the tank during our survey.
Kadamba Kulam was the largest tank surveyed (1705 acres) and is situated close to the town of Sirivaikuntam in Tuticorin District. It is a mini reservoir which feeds about 14 smaller tanks. The highest number of birds was recorded here (21,354) and about 44 species. Very large concentrations of wintering waterbirds, especially waterfowl are found here from December through February, especially large numbers of ducks such as Eurasian Wigeon, Northern Pintail, and Northern Shoveler Anas clypeata. During the dry season when all tanks fed by the Thamiraparani river go dry, birds congregate at this tank in huge numbers. At present this tank does not experience any major threat.
Arumugamangalam tank (786 acres) is situated on the Sirivaikuntam–Eral Road in Tuticorin District and supported about 26 species. This is also an important tank for migratory ducks. Large concentrations of Eurasian Wigeons were seen here. The Borassus flabellifer palm trees planted around the tank are used for nesting by a small population of Spot-billed Pelicans. Birds in this tank are threatened by poaching and more recently, the water was let out to Tuticorin City for nonagricultural purposes during the dry season, which was not done earlier.
Vijayanarayanan Periyakulam is one of the biggest tanks (819 acres) in Tirunelveli District. The second highest numbers of birds were recorded here (6,227) and about 38 species. This tank is situated close to Bird Sanctuary and hundreds of Greater Flamingoes frequent this tank occasionally. Large numbers of Bar-headed Goose were seen here and along with Koonthakulam, Nanguneri Periakulam close to Nanguneri Town, and Ponnakudi Kulam on the highway provide important wintering habitat for the geese and Common Pochards and is therefore an important tank for them in the arid landscape of south Tirunelveli District.
Along with the irrigation network, the vast expanses of salt-pans near Tuticorin and the estuarine regions of Thamiraparani are important bird habitats that need further scrutiny. The salt-pans also attract flamingoes and several species of shorebirds. In September 2010, over a few thousand waders were spotted circling in the sky in the Sagupuram area which is close to the coast and a pair of Greater Flamingoes was spotted in the salt pan in the same area in January 2011.
We list only six tanks as high priority sites because of the potential of these tanks in supporting high waterbird diversity and abundance. A total of 40,792 individuals and 67 species were recorded from these six tanks. Some of the birds seen in heronries like Vagaikulam fly off to several smaller tanks along the foothills of KMTR. Birds like the Bar-headed Goose move across a network of large tanks around Vijayanarayanam Periyakulam. There is a need to monitor these and other tanks in the region on a regular basis to identify more important sites and understand the ecological importance of the tanks better. Such monitoring has to involve a more landscape approach that would help understand the dynamics of bird movement especially related to water shortages and rainfall variability that would be relevant in the context of climate change. We could not assess how detectability due to various factors affected bird counts during our survey. Future studies designed to incorporate more robust counting techniques can assist in providing improved waterbird estimates.
Threats like poaching, over fishing, land use change, drying out tanks for agriculture by excessive pumping of water using motors which was not done earlier, etc could pose threats to waterbirds in the small tanks harboring low bird abundances. The tanks need protection since they are getting choked by invasive species like Ipomea and water hyacinth, polluted by small industrial units, tank beds are encroached on for agricultural and nonagricultural purposes. For sustaining waterbirds in the arid landscape we need to conserve such water bodies in conjunction with a network of large and/or small tanks in the near vicinity.
Our survey showed that very few tanks had trees within which serve as islands when the tank is inundated and can provide safe nesting and roosting sites. The few tanks which had trees consisted of Acacia nilotica planted by the Forest Department or Panchayat earmarked for harvesting under the social forestry scheme. These trees, used by birds for nesting and roosting are eventually harvested making the tank devoid of nesting habitats as in the case of Vagaikulam. It is imperative that forestry practices are carried out incorporating the breeding and roosting requirements of waterbirds in the area. The foreshore plantations by the forest department, that are inundated when the tank has water, have not been taken up in tanks which are either known for their heronries or have a high potential for being so. It is, therefore, necessary to revive such planting programs within the tank and its periphery with more diversity of trees and to ensure that not all trees are harvested. In smaller tanks, such plantations should be limited to a portion of the tank so that the rest of the tank is left open to be used by dabbling and diving waterbirds, and also for human activities like fishing, grazing, removal of silt for agricultural purposes during the dry season, and for domestic purposes.
Though most tanks in the areas do not require any management for bird conservation, tanks that are potential habitat (heronry) of birds are at risk. The heronry at Moondraiadippu near Tirunelveli was lost to excessive poaching, tree felling, road widening and the forest department could not intervene in time. On the other hand, the heronry at Vagaikulam was protected from contract felling by initiatives of the local communities and an NGO (Abhisheka et al. 2012). There are also some well known initiatives from local communities to protect and conserve birds in the wetlands of the region. The Koonthankulam Bird Sanctuary in Tirunelveli which is recently being protected by the State Forest Department was a community protected area (Rhenius 1907; Wilkinson 1961). Whereas in the neighboring district of Kanyakumari the forest department itself is taking initiatives to make select wetlands as conservation reserves (Kumar 2012). We need to think of various innovative measures that prevent loss of heronry and wetlands to rapid urbanization happening in the region along with improved monitoring and documentation.
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