formulation of conservation policies for wetland birds in Pulicat and in other wetlands in India.

Transcription

1 DISCUSSION

2 6.1. Imporbace o l h t Study This study provides some important information on the wetland birds of Pulicat Lake, their population over the years, habitat prcfncnces and status. This information will be useful in formulation of conservation policies for wetland birds in Pulicat and in other wetlands in India. 6.2 lmportrnce of Pulicat Lake Pulicat Lake is the second largest brackish water lagoon in India, extending over an area of 600 krn2 and is an important wetland for birds due to its large size and habitat diversity. The large extent of the lake has many different habitats such as deep water, shallow water, mudflats and mangroves. It is an ideal site to harbour species that congregate in large numbers. Since many of the birds studied, particularly the long distance migrants prefer certain habitats to others; the lake is able to attract a wide variety of migrants. The second reason why it is attractive to birds is the high organic productivity of mgicmlday. Pulicat Lake is rich in biodiversity. Many aquatic plants, vertebrates and invertebrates contribute to its biodiversity. However the lake needs to be connected to the sea to replenish the acquatic life. Otherwise there is a danger of eutrophication and eventual death of the lake. The diversity of habitats in Pulicat Lake and abundance of aquatic prey and submerged vegetation might be the reason for the abundance of Greater Flamingo (Phoenrcopterus ruber), Common Sandpiper (Actrtrs spp ), Little Stint (Cabdrrs m~nuta) (Isola et a/. 2000; Jadav and Parasharya, 2004) and others. The lake also has submerged vegetation in places that provides a habitat for other species of waterfowl. There is no floating vegetation in the lake and some species of Anatidae and Rallidae that prefer floating vegetation were not common (Sridharan, 1989; Vijayan, 1991).

3 IbsLdPbh(bs~#~~farnury kcdmipwmb.fesdinggmundtorlcng di~m~ihtwin$rhwr&mindir(r.onndmdrrpbq 1995;~~&hmd Ksnauq 2003; lsbpr mui nd 2W).The total AYmbec of birds ncmded w 21 5 species, ammg which 68 rpsoies wsn migrants. The Ldre is winarlng ground for tare and endangered species such as the Orratn Flamingo (Phocnicoplem &r), Shoveller (Anas clypeata), Sandpiper (Actitis spp.), Little Stint (Caliakis mimcta), Grey Pelican (Pelecanusphilippensis), Grey Hsmn (Ardea cinerea), Curlew (Numeniw arquata) and others. Thc Lake is also feeding ground for thc Grey Pelican (Pelecanus philippewis), White Ibis (Threskiomis ae~h~opica melanocephalus), Openbill Stork (Anastomus oscitaw), Coot (Fulica atra) and Little Grebe (Tachybapfus nrficollis). There are breeding colonies of Grey Herons (Ardea cinerea) at Bodilingalapadu near Tada and Painted Storks (Mycteria leucocephala) at Nelapattu Bird sanctuary, close to the lake (Figure I). Pulicat Lake is the breeding ground for other local migrants such as Little Grebe (Tachybaptus ruficollis), Cormorants (Phalacrocorm sp.), Large Egret (Ardea alba) etc. 6.3 (a) Population Trend This study has shown that there is an alarming decline in the populations of certain species over the six year period. The reason for this decline is not known. It could be an artifact of the sampling procedure since samples from a selected week in February were used for the analysis. However a consistent pattern of decline indicates that this is a real trend and one that should be taken into account by conservationists and ornithologists. Many of the species such as the Greater Flamingo and the Grey Pelican, whose populations show a declining trend, are endangered. The decline could be either because Pulicat Lake is not an attractive destination for wetland birds any more, or because there is a global decline in these species, reflected in their population sizes in the Lake. Among the factors that are possibly reducing the attraction of Pulicat Lake for birds are siltation of the lake bed resulting in the closure of the mouth of the estuary reducing salt water mixing (Sanjecva Raj, ), over-fishing and subsequent reduction in resources (Manakadan

4 adkmup,20ea),~efmq~mcbehltstucdrom~llttbia~ion ~fthe~~sboo).hlrrlkogaiagofrq~rwlcungnnshlwnwltcdinwrter pollution (wandbmm, 2000). Ovar Ming in drs Wie has df& m y quatic clpecics that an food forthe birds (ilghwriah, 2000; Mmluxb tnd Wnm, 2003). All these dish~rbance factors might be the rsclsclllo for decrease in bird population in the hke. On the other hand these birds might be declining due to factors in their summer bntd~n grounds. during miption or due to other factors. This has to k examined closely for suitable lnterventlons to be carried out. 6.3 (b) Relatlve Abundance In the present study, about 27 common wetland b~rd specles were studled All of these specles were common and preferred estuar~es Among these were the Greater Flamingo (Phoenrcopferus wber), Grey Pellcan (Pelecanusphilrppenrrs), and Wh~te lb~s (Thresk~omis aethoroplca melanocephalus) and Palntcd Stork (Mycferra leucocephala) wh~ch are rare and threatened specles In the subcontlnent (Arunkumar el a1 2003) Many of the specles listed as rare, were also rare elsewhere In the subcont~nent (Prakash Rao, 1998, Anin Kumar et a1 2003) Rar~ty was not related w~t habltat spec~allzat~on Most of the specles studled, including the common and rare were habltat spec~allsts whlle the very common blrds were hab~tat general~sts Spec~es w~th narrow range of habltat preferences were not necessarily those w~th low abundances (Brown, 1984) The rare specles were not necessar~ly spec~ailzed w~th regard to food Many specles, both common and rare were generalists w~th regard to food The majority of the very common specles were fwd spec~allsts Therefore ne~ther habltat nor food spec~al~zatlon was related to commonness and rarlty Pulicat Lake probably attracts these specles because there are a broad range of hab~tats and food types for the blrds to utli~se

5 ~~riacdmionmyuteedlywssenotm~.~diimigants tended to bah hmhtd Common sp~l. This is probrbly bcwm these species belonging to different fuailies bad distinctive MMviouml pmam Some wsn s oli and others w e wcid which pbrbly w~1tsdforb differences. The mrjority lmal migrants wen very common and common. 'Ilk might be because many local migrants on colonially nesting species and tend to be in flocks. Spoonbill (PlaMlea leucorodia). Spot-bilkd Duck (Anas porcilorhyncha) and Red shank (Dingo totanus) were few in number. These birds are usually solitary or in pairs and do not congregate in large numbers. 6.3 (c) Seasonality The lake seems to be highly suitable for migrants. The period of migration coincides with the N. E. monsoon which is a productive period for the lake. Many investigations reported that during winter, productivity of lakes in the Indian subcontinent increases, attracting a large number of birds (Peacock, 1963; Kaliyamurthy, 1973; Kushlan et a1 1975; 1976; 1978; Ogden et a/. 1978; Vijayan 1991; Narasimhulu, 1995). During the winter availability of food resources may be more and physio-chemical factors might be highly suitable for acquatic diversity. Presence of water in the Lake appears to be major factor in availability of food resources, and for the arrival and departure of migrants. There were more partial migrants than residents indicating that the lake provides a good feeding habitat but might not be conducive to support a breeding population of these birds. Some species such as Grey Pelican (Pelecanur philippensis), Painted Stork (Mycteria leucocephala), and White Ibis (Threskiornis aerhiopica melanocephalus) feed on the resources in the tanks, ponds and rice fields locally which act as feeding grounds (Sanjecva Raj, ; Manakadan and Kannan, 2003). This may the reason for the presence of these species even after the lake dries UP.

6 6.3 (d) 8psda finsra WImt Puliut Ldre ptklty Bks up, woot of the birds luvc the Lake wly (Kaliymuthy, 1974; Nansimhnlu, 1995; Sanjcm Rj, , Nan& Kwnar, 22001). The stable popumons from April -July could be bcuuse only species that can adapt to low water levels and loss of pmductivity of the Inkc remain thm. Them is a high turnover of species during the migratory period indicating that the lake is used by many species as a transient point to wetlands further south. Therefore the location of the lake is probably important for passage migrants transiting to sites further south such as Point Calimere. 6.3 (e) Habitat Preferences Habitat preference of birds was more at the family level. Among the families 10 were habitat specialists, 3 were generalists. Other studies support our findings regarding habitat preferences of many of the species (Sridharan, 1989; Vijayan, 1991; Safran et ; Isola, 1998; Wills. 1999; Guillemain et al. 2000). Our study confirms the findings of other studies that small sized birds preferred mudflats (Baker,1979; Isola, 2000; Poysa, 2003). All the generalists were large sized birds. Because of their large size body these species might be able to use all types of habitats. All the specialists were surface feeders and waders. Because of their wading behavior waders might be using mudflats. Having specialized feeding techniques, the ducks, are able to forage in deep waters. Both the Greater Flamingo (Phoenicopterur ruber) and Shoveller (Anas clypeata) used deepishallow waters due to their large sized body and feeding technique. Many of the species preferring deep water or shallow water were also recorded in mudflats which they use for resting or d~ying their wings in the absence of trees in the Lake. The Grey Pelican (Pelecanusphilippensis), Painted Stork (Mycrerio leucocephala) and others were also seen in shallow pools under culverts, when the lake was drying up, where they could more easily catch Ash trapped in the pools.

7 ~ a r l y h r 0 ~ ~ ~ w t a ; r m x h ~ o f b i r d s w q c found in rhlkv nnta(3nl bbds-ba2) G8Howcd by mudm (2891 binis-km'). This is because Gnater Flamingo (Phocnleoprenu k r ) which was the most abundant sp#ics prcfcmd shallow water. 'hmforc slullow wrtsr is wry importlnt Lbiut for consewation of the Oltatcr Flamingo (Phoenicoprenu rrrbcr). High bird dcnsftios in smbw water and mudtlats an h s c of high biological productivity of these habitats. Anatidac also used both deep water and shallow water (Appendix 6). Shoveller (Anar clypeata) used deep water and shallow water and the Spotbilled Stork used deep water only. Similarly Scolopacidae preferred mudflats but certain species (Sandpiper) used shallow water and exposed mudflats also. 6.3 (f) Habltat use and Feedlng Genenlimtlon Long distance migrants tended to be habitat specialists whereas the residents were mostly generalists (Table 12 ). All the abundant and very common bird species were specialists. All the uncommon and rare species were generalists. Therefore Pulicat Lake has the requisite habitat diversity to attract the long distance migrants that tend to be more habitat specialists. Since the wetland is large and has deep water, shallow water, mudflats and other habitats, the Pulicat Lake is able to support large numbers of long distance migrants that were very abundant in the winter season. These species arrive in congregations and the majority were food type generalists. That means the habitat use was not related to food preferences. Therefore each of the species might be using a particular habitat to forage for a wide variety of food types (Chapman and Reiss, 1995). Due to the habitat specialization, species are more efficiently able to use the available space in the lake and avoid overlap. This might lower inter-specific competition for resources. All local migrants were habitat specialists, but half of them were specialists in food prefmnces. Local tanks, ponds and rivers are also feeding grounds for the local migrants

8 (Shqbw Raj, 1 W, hhddm, byaity of long diqlna mi- fwd few wading bbds were spcllim. hw gmmlizcd 6.4 Couuvltb. ud M8mgement d wrkr Mrd# It is very important to maintain the size of Pulicat M e and prevent it from being encroached. The size of the Lake is important for maintaining habitat diversity and productivity and for attracting large congregations of ran and endangered waterfowl. Majority ofthe migrant species prefer deep water and mudflats. Maintenance of these habitats is very important for the conservation of water birds. Though the Pulicat Lake has been legally protected as a Wildlife Sanctuary and falls under the category 1 of Coastal Regulatory Zone, efforts have to be made to manage the Pulicat lake to attract a diversity of waterfowl. Encroachments of the lake bed, siltation, formation of roads across the lake, pollution and other human impacts may reduce the available habitat for birds which will result in fewer migratory birds visiting the lake. Gradual decrease in water bird population during the period 1995 to 2000 is a major concern. Therefore stringent protection and management of the lake to promote habitat diversity are required. Sand accumulation across the mouth of the lake and early drying up of lake is a threat to the bird population (Ramesh. 1994). Keeping the channel to the sea open throughout the year is vital for the inflow of water and for the maintenance of biodiversity. Sludge removal in a channel (Sanjeeva Raj, 2001) at the mouth of the lake is required to maintain the inflow of water. Periodical maintenance of the open channel with involvement of local people is necessary. Connection with the sea is necessary for bringing in micro-organisms and fish into the lake upon which the birds depend. Management options that enhance the zooplankton production is highly valuable for wintering migrants. Over-fishing of fish and shrimps remove food for the migratory birds and make them search for new habitats (Goss -Custard, 1977; Percival eta/. 1996; Sutherland, 1996: Workshop,

9 2003). Food dnn&bnw b of crucirl LnpgQnCc for winter Wi selscth by mipntory birds (Chillman et ol. 2000). Catohhrg of fmprlings using mall mesh nets is a problem in this lake.?hasfwe, ban on small size nets has to k impowl, no fishing wnes an to be decland (Manakadan and Kannan, 2003; Wofkshop, 2003) and alternative income generation programmes an to be initiated for the fishermen to reduce pressure on the Lske. Effons may be made to motivate the fishermen to resume the ancient traditional management practices once again. The Lake is silting up at an alarming rate, thereby reducing the extent of habitat for wetland birds. Siltation is mainly from three rivers draining into the Lake (Sanjeeva Raj, ) and by ovefflow from the surrounding agricultural fields. Therefore, siltation of lake has to be controlled. Planting of mangroves (Narasimhulu, 1985) in the areas near the rivulets entering into the lake i.e., in between the areas from Vatnmbedu to Bheemuiavaripalem need to be carried out on a priority basis. Mangroves present on the eastern side of the lake serves as good breeding ground for prawns because the fallen leaves and litter are the source of rich proteinous food for prawns (Simberloff, 1983; Narasimhulu. 1985). Hence it is essential to see that the mangroves are protected. This study clearly indicates that Pulicat Lake is a very important wetland for birds in the Indian subcontinent and has to be well managed to maintain the bird diversity.