Effects of a Cyclone on Waterbird Populations at the Pichavaram Mangroves, Southern India
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Effects of a cyclone on waterbird populations at the Pichavaram mangroves, southern India KrishnamoorthyThiyagesan and RajarathinaveluNagarajan Thiyagesan,K. and Nagarajan,R. 1997. Effectsof a cycloneon waterbirdpopulations at the Pichavaram mangroves,southern India. Wader Study Group Bull. 84:47-51 A severecyclone hit the Coramandalcoast of Tamilnadu,southern India on 4 December1993. The impactof this cyclone on the waterbirdpopulations of Pichavarammangrove forests was studied. Waterbirdnumbers and speciesrichness and speciesdiversity in 1994 were comparedwith censusdata collectedin 1993 and 1995 censusi.e. beforeand after the cycloneevent. The waterbirdpopulation in the area was 4,883 in January 1993, 3,060 in January 1994 and 5,091 in January 1995. The speciesrichness and speciesdiversity during 1994 was also lowerthan in the othertwo years. Althoughthe speciesrichness and speciesdiversity of these mangrovesreturned to normal after the cyclone,continuous monitoringof the bird populationsin this area is neededfor a few more years beforearriving at a definiteconclusion. KdshnamoorthyThiyagesan, Division of IA41dlifeBiology, A. V.C. College,Mannampandal- 609 305, Tarnilnadu,India; RajarathinaveluNagaran, Divisionof IA41dlifeBiology, A. V.C. College, Mannarnpandal-609 305, Tarnilnadu,India. Present address:Department of Psychology, WashingtonSinger Laboratories, University of Exeter, Exeter-E)('44QG, UnitedK•hgdom groundsattracting these birdsspecies (Nagarajan & INTRODUCTION Thiyagesan 1994). Natural calamities such as floods. forest fires and Descriptionof the cyclone earthquakesare knownto result in bird mortality(Roberts 1932; Alexander 1948; Smith & Webster 1955; Merrill A severe cyclonehit the Coramandal coast of India on 4 196,1;Stout & Cornwell 1976; Higgins& Johnson 1978; December1993 causingunprecedented devastation. A Johnson 1979; Welty 1982; D'Cunha & Akhtar 1987; portionof Coramandalcoast sufferedthe impact of the Rammanohar& Rajasekaran1989). This paper describes cyclonethat crossedthe shore betweenNagapattinam the effects of the cyclone of 4 December 1993 on waterbird (10 ø46'N;79 ø53'E) and Cuddalore(11 '43'.N; 79' 53'E). populations at the Pichavarammangroves. southern The cyclonewas accompaniedby a torrentialdownpour India. and winds of up to 70 kmlhr, and it continuedfrom 0300 to 1145. Huge storm-waveswere generated by the Location of the Pichavaram mangroves cyclonewhich caused major structuraldamage to the Pichavarammangroves. The brackishwaves and 150mm The Pichavarammangroves (11ø25'N; 74 ø47'E) are of rain inundatedseveral coastal areas and the nearby situated about 190 km south of Madras at the mouth of agriculturallands and settlementsfor three days. the Vellar, Coleroonand Uppanar riverson the southeast coast, knownas the Coramandalcoast (Bay of Bengal), of Waterbirdnumbers before and after the cyclone India(Figure 1). They are the only large area of mangroves, coveringan area of 11,000 ha, with 51 islets It was observedand reportedby the nearbyvillagers that separated by'a complex networkof creeks and channels many birdsat the Pichavarammangroves died becauseof (Figure 1). As Figure 1 shows, interspersedin this forest the cyclone,as many plantswere uprootedand/or their area, there are many types of wetland habitats such as branchesand canopyseverely damaged. Furthermore, swamps, marshy areas, estuaries,intertidal mudflats and the strong gale created panic and confusionamong the open waters (Wolstencroftet al. 1989), offeringa wide birdsand they were dashed againstthe trees and/or variety of roostingand nestingplaces and foraging adjoiningbuildings, as they were unableto controltheir groundsfor several migratoryand residentbird species flight. As a resultthe birds died.instantly or were badly (Nagarajan& Thiyagesan1996). The adjacentcroplands injured,fell intothe floodsand becameunable to escape, and abandonedfields also act as potentialforaging or were caughtby nomadicpeople and villagers. Some birdswere totallyemaciated and died becauseof exhaustion,fatigue and starvation. 47 In order to assess the impacts of the cycloneon the cinerea, Little Egret Egretta garzetta, Cattle Egret waterbirds of the Pichavram mangroves,waterbird counts Bubulcusibis, Painted Stork Mycterialeucocephala, Asian were made a month after the cyclone,in January 1994. Open-billedStork Anastomusosc/tans and Black-headed They were carried out using7x50 field binocularseither Ibis Threskiomismelanocephalus, it might also have from a boat or by walking along the edges of the wetlands. caused severe damage to their nests, eggs and young. The data collectedwere comparedwith censusdata from .• 1993 and 1995 for the same area, which we collected as The Pichavaram mangrovesare an importantwintering part of the Asian MidwinterWaterbird Census. Species area for many migratorybirds whose annual peak richness was measured as the number of waterbird occurrenceis usually during Novemberto January species recordedduring the census (Verner 1985). (Sampath & Krishinamurthy,1990, 1992; Nagarajan& Species diversitywas calculatedusing the Shannon- Thiyagesan 1994, 1996). Thus, it was feared that since Wiener index (Shannon & Wiener 1949). the cycloneoccurred during that period it might also have had significanteffects on the arian migration patterns on s this peninsula(Nagarajan & Thiyagesan1995). H'= -•.(pi)(Iog 2Pi) i=1 However, the birds seemed to have recovered from this event, as the species richnessand speciesdiversity as s = number of species well as the number of waterbirdsvisiting these mangrove pi = proportionof individualsof a given returnedto normal or even higher values during 1995. species However,continuous monitoring of the bird populationsin this area is neededfor a few more years, beforearriving at The differencesin the waterbird populationand species a definite conclusion. compositionbetween the years were analysed by the General Linear Model usingthe statisticalprogram MINITAB (Ryan et al. 1992) and a planned comparison test was done to comparethe mean populationof the ACKNOVVLEDGEMENTS cycloneyear with other years. We thank ProfessorStephen E.G. Lea, Departmentof Table 1 showsthe three years' censusdata groupedby Psychology,University of Exeter, Englandfor comments speciesi.e. herons& egrets;storks; shorebirds; and gulls and statistical advice, and R. Sivasankaran for field & terns. The estimatedtotal waterbirdpopulation in the assistance. area was 4,883 in January 1993, 3,060 in January 1994 and 5,091 in January 1995. The waterbirdspecies richnesswas 26 in January 1993, 24 in January 1994 and 29 duringJanuary 1995. Waterbird speciesdiversity (H') was 2.23, 2.02 and 2.38 duringJanuary 1993, 1994 and REFERENCES 1995 respectively(Table 1). There were significant variationsin the waterbirdpopulation between years Alexander,W.B. 1948. The indexof Heron population,1947. BritiSh (General linear model F=9.89, P<0.001)and species Birds 41: 146-1 48. (General linear model F=69.91, P<0.001). The mean Bailey,E.P. and Davenport,G.H.1972. Die-offof commonmuffes on waterbird populationin the year of the cyclonei.e. January the Alaska Peninsula and Unimak Island. Condor74:215-219. 1994 was significantlylower than the other two years (F=19.60, P<0.001; Planned comparison). D'Cunha,E.P.E. and Akhtar,A. 1987. 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