Selection of Suitable Census Method for the Indian Sarus Crane Grus Antigone Antigone

5 Pages·2001·3 MB·

by  Aeshita Mukherjee

SELECTION OF SUITABLE CENSUS METHOD FOR THE INDIAN SARUS
CRANE GRUSANTIGONEANTIGONE'
AeshitaMukherjee,C.K. Borad, S.B. PatelandB.M. Parasharya2
(With one text-figure)
Key words: Grus antigone antigone census method, noon count, night roost,
,
population density, paddy crop, summer months, reservoirs
An estimation ofthepopulation sizeoftheIndian saruscraneGrusantigoneantigonewas
done in thesummerof1997 and 1998. Atotal of432 and457 craneswerecounted, in the
526 sq. km areaofKhedadistrict, Gujarat,during hothours(1200-1600 hrs) in 1997 and
1998 respectively. Night roost count at reservoirs (548) was higher than the day roost
count. Results suggested that for accurate population estimation, the night roost count is
better, buttimeand man powerrequirementscan bea limitation. Fora large scalecensus,
the dayroost count atreservoirs andtheir environs could be better.
Introduction We attempted to determine the total
population using two different methods. This
Estimationofavianpopulationisthebasic paper describes the merits and demerits ofboth
requirementto initiate any study leadingtotheir the methods selected for determining the sarus
conservation. Qualitative statements regarding crane population and density.
status and distribution do not give a true picture
ofthepopulationsize, irrespectiveofthespecies MaterialandMethods
studied. To decide conservation management
strategies, it is necessary to estimate the actual The census was done during the summer
population size at a given site at the right time. monthsApril,MayandJune 1997andMay 1998.
With a drastic reduction in its distributionrange Cranes encountered along the road and in and
andatotalof12,000individualsworldwide(Gole around reservoirs were counted within the four
1989, 1991), the Indian sarus crane Grus hour period of 1200-1600 hours (hot hours) in
antigoneantigoneisnowconsideredasaglobally oneday. Ifanareawasleftuncoveredduringthe
threatened species (Meine andArchibald 1996). stipulated time period, it was completed on the
Despiteseverallimitationsinthecensusmethod, nextday.Thecranesconcentratedchieflyaround
attempts have been made to estimate the sarus fivemajorreservoirs.Hence,themaximumcrane
crane population in Gujarat State (Vaishnav count around any of these reservoirs, in a
1985) and its distribution range in India (Gole particular month, was taken into consideration
1989). In Kheda district, the sarus crane density during the census of 1997. At the same time,
onafixedroute hadbeenattempted(Parasharya carewastakentoensurethatthecranepopulation
et al. 1996) along with population estimation. in the adjacent area was counted as a separate
m
Here we have attempted to estimate the sarus population. Cranes sighted within 800 on
cranepopulationinMatartehsilofKhedadistrict either side ofthe road were also counted. The
to supplement the above study during summer presenceandgrowthstageofpaddycropsaround
intwo successive years. the census area were noted to understand the
crane distribution pattern. During 1998, counts
'AcceptedMarch1999 were done onlyon 24-25 May.
2AINPonAgriculturalOrnithology,
Night roost counts were attempted at 16
GujaratAgriculturalUniversity,
Anand388 110,Gujarat,India reservoirs from May 17-24, 1998. Unlike the
JOURNAL, BOMBAYNATURAL HISTORYSOCIETY, 98(2), AUG.2001 237
)
CENSUSMETHODFORTHEINDIANSARDSCRANE
noon count, in which one person could count Table1
POPULATIONESTIMATIONOFSARUSCRANE
cranesonseveralreservoirsinafourhourperiod, DURINGNOONHOURSOFSUMMERMONTHSIN
ittookonepersontoestimatetheroostingcranes KHEDADISTRICT,GUJARAT
at a particular reservoir in one night. Thus, the
No.ofcranesobserved
three individuals involved could survey only
Sites 1997 1998
three reservoirs in a single day. All the cranes
1. Bhanderaj(R) 76 79
present in the reservoir and the ones arriving Suuoundingarea 3 4
were counted till itwas totally dark. The sun set 2. Narda(R) 135 0
at 1912-1916 hours during the count period. Surroundingarea 17 21
3. Gobrapura(R) 0 0
Surroundingarea 40 138
StudyArea 4. Daloli(R) 65 105
Surroundingarea 6 8
5. Traj(R) 44 0
The study was conducted in a 526.03 sq. Surroundingarea 9 1
kmareaspreadoverMatar,KhambhatandPetlad 6. Pariej(R) 0 0
Surroundingarea 2 6
tehsil of Kheda district, Gujarat. Major 7. Kanewal(R) 0 0
reservoirs, at which the study was conducted, Surroundingarea 23 15
along with the main roads, are shown in Fig. 1. 8. Others(R) 12 80
Total 432 457
Thestudyareahasthebenefitofwellestablished
branching canals terminating in reservoirs. The During both years, the crane number was
landscape is plain, low lying and suitable for highest inNarda-Gobrapura and its surrounding
paddy crop (Oryza sativa cultivation during complex, proving it to be an important area
monsoon due to irrigation facilities. During the (Table 1). Bhanderaj and Daloli also supported
southwest monsoon (July to September), the a high number ofcranes. Though Kanewal and
whole area gets flooded and remains so till late Pariej were the largestreservoirs, the numberof
September. In the summer (April to June), the cranes present here were insignificant, as both
reservoirs retain some water, at least at the reservoirs have a very greatwater depth and
miniumumlevel.Dependingonlocalconditions, lacksuitableroostingsites. Theyarealso subject
paddy crop is grown in the command area of to continuous human interference, especially
somereservoirseveninsummer.Thetemperature disturbance from fishing.
reaches 45.6 °C, particularly in May. The cranes which concentrated at the
Narda reservoirand its environs in 1997 shifted
Results to Gobrapura in 1998. Similarly, the cranes at
Traj and its environs shifted to Machhial. Both
Population estimation during hot hours theshiftswerewithin5-6km,andwereprobably
in summer: The sarus crane population in the duetochanges inthe waterlevelofthereservoir
study area (526.03 sq. km) in 1997 was 432, and the paddy crops around it. The crane count,
while in 1998 it was 457 (Table 1), and had a atthefivereservoirs,wasfairlyhighandconstant
density of 0.82 /sq. km to 0.87 /sq. km cranes during the study period.
respectively. The difference in the numbers All these reservoirs are situated within a
sighted between the two years was negligible. range of5-15 km from each other, but still hold
Moreover, this was the minimum population adistinctpopulation,suggestingthatsaruscranes
estimated, as only the actually seen cranes were are highly sedentary and restricted in their
counted. activity around a particular reservoir.
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In the summer, due to heat and stress, the Table2
POPULATIONESTIMATIONOF
cranesconcentratedaroundthereservoirsinlarge
ROOSTINGSARUSCRANE,DURINGSUMMER,
flocks, which aided the census. However, the INKHEDADISTRICT,GUJARAT
paddy crops growing around the reservoirs also
Site Cranenumber
provided a suitable protected habitat from the
Bhanderaj 133
heat, which was evident from the count in the Narda 51
surrounding area. Gobrapura 60
Population estimation during night Daloli 152
Traj 00
roosting in summer: As it was a dry period, all Pariej 02
the cranes converged to the reservoirs for Kanewal 04
roosting. Sixteenreservoirsspreadoverthestudy Tranja 02
area were monitored to count the roosting sarus Salla 12
Naghrama 04
population, hence no flock was missed fromthe
Heranj 00
total estimate. A total of 548 sarus crane were Khandhli 00
counted, giving a density of 1.04 /sq. kmduring Garmala 02
Machhial 92
a night roost count.
Vasai 09
About 65% of the cranes concentrated
Barson-Baroda 25
chiefly around 4 major reservoirs, the Daloli,
Total 548
Gobrapura, Narda and Machhial (Table 2). The
area important for day roosting, was also found ofsummer, the sarus cranes are known to flock
significantfornightroosting. Anotherimportant in the wetlands (Ramachandran and Vijayan
site was Bhanderaj, whichhad 24% ofthe sarus 1994, Mukherjee et al. 1999, in press).
%
cranes atnight. 11 were distributed in 8 small In summer, the cranes move far off for
reservoirs. foraging during the morning andevening hours,
Three reservoirs, though they had but they returned to the reservoirs from 1200
sufficientwater,werenotusedbythecranes.The hours onwards (Mukherjee etal. 1999). Once at
sarus cranes numbers at a particular reservoir the reservoir, the cranes did not show any
were determinedby its water level and suitable, movementforfourhours andhence, thechances
safe roosting sites. AtBarson-Baroda the cranes ofcountduplicationwerenegligible. Fourhours
roosted in the shallow waters ofthe river basin. are sufficient to travel across the study area to
It was the only site ofthe riverine area that we estimatethepopulationinthereservoirandalong
examined for the night roost. The number of theroute.Twopersonswithavehicleneededtwo
cranes estimatedduringthenightroostwas 16% days to complete the count in the 526.03 sq. km
higher than the count during the day roost. area. Hence, saruscrane censusduringhothours
(1200-1600 hours) in the summer is ideal.
Discussion Limited man power and time frame placed
restrictions on the size ofthe area which could
During summer, the water was available besurveyed.
only in the reservoir or in the paddy crops The cranes utilised the summer paddy
growing around the reservoirs. To avoid heat crops during the hothours, both as foraging and
stress, the cranes flocked in the reservoirs or in roosting ground leading to a dispersed
the paddy crop, enabling an almost accurate distribution, which subsequently caused
population estimation. To avoid the heat stress underestimation ofthe population size. During
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CENSUSMETHODFORTHEINDIANSARUSCRANE
the summer of 1997, paddy was grown around the protection and conservation of the sarus
most of the reservoirs making accurate counts crane.
difficult. However, in 1998, the cultivated area It is worth noting that in the 526.03 sq.
was limited, hence counting was easy. km ofthe study area, paddy was the only crop
In 1998, along with the day roost counts, grown during monsoon. It was also grown in
night roost counts were made to overcome this patches around reservoirs during summer. All
drawback. For accurate population estimate, we the wetlands retained some level ofwater even
made nightroost counts in all the 16 reservoirs. insummer.However, onlyafewreservoirswere
Thecranecountduringnightroostwascertainly used by the cranes for roosting. Crane
higher than the day roost count. However, the distribution was patchy, indicating that the
one person to one reservoir ratio is time presence of water in the reservoirs or in the
consuming and requires more man power. Our paddy crop around reservoir are not the only
nightroostcounts couldbe accurate, as we were factors responsible for the crane abundance /
familiarwiththestudysiteandwiththedirection distribution. Gole (1989) had developed a
of the arriving cranes. Night roost counts can formula to estimate crane population based on
possibly be difficult in an unknown area, but in crane density derivedthroughroadtransect and
the present case, they were more accurate than total wetland area separately. On the contrary,
the day roost count. our study revealed that even though several
There was a difference ofonly 91 cranes wetlands existed, some were not utilised by
inthecountsbytwomethods. Thisindicatesthat cranes. Therefore, the earlier report by Gole
the sarus is sedentary, does not show frequent (1989) may represent an inaccurate count.
movements and prefers the same area for day Recently, Mukherjee et al. (in press) had
andnightroosting.Atleastinthesummer,cranes established apositive correlationbetween sarus
hardlydispersed5-6kmfromthereservoir.They crane abundance and percentage land under
also had an affinity for the water bodies for irrigated paddy crop, as well as visibility index
roosting. The same was seen around Bhanderaj, / openness of the habitat. However, we found
the only reservoir which ultimately attracted thatinsummer, factorslikeflocking,availability
cranes from all over the area. Thus, the study ofpaddy crop and time of the day influenced
highlightedthe importanceofthesewetlandsfor the crane numbers counted.
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