U. Sirivardana and Uditha Hettige - CBCN February 2010 pages 52, 53-a to g, 53

Visit

Thushara Senanayake, Palitha Antony and the two authors were carrying out the annual waterbird census for the Mannar region in 2010 for the Ceylon Bird Club. We wished to follow up on the report in January of very large numbers of migrant shorebirds in the Vidattaltivu Lagoon, then seen briefly and from afar. The site had never been visited for the census nor surveyed for its birds.

We visited it on February 5th at c. 3 p.m. It was decided that the count here would be done by U.H., T.S. and U.S., the last-named writing field notes.

The view had been from the north-eastern end of the Army buildings near the water. From here we, too, could see similar numbers of birds. We walked farther east along the open area, with the lagoon on our left. As we did so more of the water could be seen, and more birds in it came into view. Because of heat haze and distance we could at first only make out that the numbers were extra­ordinary. We kept moving, and could soon see that there were several 100,000s, a record for Sri Lanka.

Count

It was quite sunny when we arrived, but within an hour the light dimi­nished due to cloud cover.
To avoid alarming the birds, and also because the shore was wet (from the receding tide) we did not get close to the water.
The count was begun from the platform of a temporary watchtower c. 500 m away from the Army build­ings, at a height of c. 3 m. The birds were from c. 250 m to 2 km away from us.

They were grouped roughly in several large rows parallel to our shore. one behind the other, with gaps (where there were very few or no birds) between the rows. In each row the birds were many "deep", this number varying within the row across its spread.

The count was planned out and mostly done by U.H. We began by count-ing the birds in the first row, even before we could discern the number of "rows". If the birds moved away soon we would have at least have counted that row or part of it. We would also develop an idea and "feel" of the con­centrations of birds present.

First U.H. marked out a group of birds which was estimated to be c. 1,000 through his binocular (a Swarovski 8.5x 42), and which nearly coincided with one full view through his tele­scope (a Kowa TSN4 20-60x 77mm: zoom setting not noted). He counted them: it was 980 left to right, 834 right to left, average 907. T.S. and U.S. re-counted them, through another telescope (a ZT 8-24x 40mm: zoom level not noted) and the former, and each obtained a figure very close to U.H's average.

U.H. scanned to the right marking out 10 such groups consecutively, and this figure was checked by U.S. through his binocular (a Nikon 8x 25). The concentration of birds in some of these was clearly more than in the first. Hence the number of birds in the larger group was estimated as follows: 907 x 10 = c. 9,000, adjusted upward to 10,000.

Walking farther east, U.H. marked out more of these larger groups in the first "row", by size and concentration, as carefully as possible. U.S. did so more quickly, and the results agreed. The row had 10-11 such groups. Hence the number of birds in that row was estimated, in this way, to be 10,000 x 10 to 11 = 100 to 110,000.

C. 1 km away was a sandbank roughly parallel to our shore. From the tower we could see that between our shore and this bank there were at least three other "rows" of the same size or a little larger, and that the con­centration of birds in the second and third rows (away from us) was higher than in the first, after adjusting down for perspective.

We walked to the next vantage position, which was Army watchtower "Point 55", c. 200m far­ther on, or east.

This was nearer to the farther end of the "rows". The birds at that end of the first row in one full scope view from the new perspective was counted by U.H. The figure was 919, which we rounded to 900 in the conditions.

Noting groups of this size one by one, as before but now scanning right to left, a larger group of these groups was again chosen, which was found to be convenient to mark out visually from this angle, after quickly surveying the whole of the first row. This larger group had 13 of the smal­ler. Hence, the number of birds in it was estimated to be 900 x 13 = c. 11,700. We saw the row to have nine of these exactly (subject to the scale of accuracy achieved). Hence by this method the estimate for the first row was 11,700 x 9 = 105,300, rounded to 105,000.

The close agreement of the results by the two methods - subject to the un­avoidable imperfections - gave us confidence that we could continue to count the rest of the birds, on - unavoidably again - a larger scale.

From the second tower we could see that there was a fifth "row" of birds, that the total number of birds in this, too, was higher than in the first, and also that there were many other birds not seen from the first tower, which were behind a stand of mangroves to the left of our "rows".

The population of birds back until the sandbank was estimated as fol­lows. In the rows were at least 105,000 x 5 = 525,000. The excess in the higher concentrations of rows two, three and five, and behind the man­groves was estimated as between 25,000 and 75,000. Hence the total was 550 to 600,000 birds.

Behind the sandbank was again a vast number of birds. They, too, were subjected to lengthy and careful surveys. The distances of their spread sideways and back away from us were estimated to be about the same as in the nearer set assessed above. These were confirmed later on examining a satellite image. The average concentration of birds within this set, too, was estimated to be about the same as the first. Further, they spread out of sight to our left behind a stand of mangroves or shrubs on the sandbank. A satellite photo showed that the habitat they occupied extended well into this area. Hence we estimated the number of birds behind the sandbank to be at least another 550 to 600,000.

The total can thus be stated to be 1,100,000 to 1,200,000 birds.

The count and calculations (all on site) took from 3.35 to 4.55 p.m.

A few days later U.S. wrote to Simon Delany, an international expert on water­bird population estimates (at Wetlands International, who co-ordi­nate the census globally), summarising the above and requesting his frank opinion on our methods. The three most important points in his reply are as follows. The "army watchtowers probably made a big differ­ence to the quality of counting that was possible. It helps a lot to have even a modestly high vantage point."

"One difficulty ... is keeping track of which birds you have counted and which remain un­counted, especially as you move from vantage point to vantage point - this is easier if there are distinc­tive markers such as channels, rocks, buoys or posts to help divide the area up into countable units." For the first 'row' this was a problem, but the agreement of our two results shows that despite this we seem to have done well enough.

The "proportion of extrapolation in this count was (inevitably and very understandably) quite high - in particular, [how the birds behind the sandbank were assessed] implies that it was not pos­sible to count half the birds in a detailed way and this proportion was estimated from those already counted - which is an acceptable method, but on this scale it will (of course) limit the accuracy of the results."

Although U.H. and T.S. had cameras, photographs which may have given an idea of the numbers of birds on this day were unfortunately not taken, because firstly, changing to suitable lenses would delay the counting, and after­wards, light conditions were poor.


Species

Before the count several species present were identified quickly. During it identification was constantly done, but this was less urgent than count-ing all the birds, i.e. we did not let it hinder that process.

Cursorily while taking the totals, and carefully by U.H. after this had been achieved, estimates were made of the proportion of the number of individuals of each of several species present in the totals. Our percen­tages, and the populations resulting from these, are as follows, for the total forward of the sandbank. This was taken now as 550,000, to be conservative in these figures.

Curlew Sandpiper Calidris ferruginea          65%  357,500
Little Stint Calidris minuta                           10%    55,000
Lesser Sand Plover Charadrius mongolus    5%    27,500
Common Redshank Tringa totanus              5%    27,500
Marsh Sandpiper Tringa stagnatilis             5%    27,500.

On arrival at the first tower we had counted an estimated 2,000 Grey Plover Pluvialis squatarola.

Other species identified were: Common Greenshank Tringa nebularia, Asiatic Golden Plover Pluvialis fulva, Kentish Plover Charadrius alexan­drinus, Little Ringed Plover Charadrius dubius, Black-winged Stilt Himan-topus himantopus, c. 50 Avocet Recurvirostra avosetta and a few Com­mon Sandpiper Actitis hypoleucos.

The birds behind the sandbank were too indistinct to be identified.

In the analysis of experts on the populations of water­bird species and subspecies the approximate number of Curlew Sandpiper migrating in the Northern winter to the South Asia region has until now been esti­mated at 250,000. Our figure for this site in this census is 1.4 times that! The figures for the other four species in the table above as a pro­portion of such estimates are, respectively: 0.22, 0.27, 0.21 and 0.27.

That estimate for the Curlew Sandpiper is thus shown to be incorrect. Our figures for the other four species are, for one site, very high propor-tions of their estimates. Those, also, had been made with the best avail-able information. They may possibly be correct, or they too, may thus possibly be in need of revision. The distribution of these species within the South Asia region is monitored mainly by this census, co-ordinated among its countries by Wetlands International. The figures for these species in other parts of the region this season are not available yet.

Apart from those which we identified, a gathering of shorebirds on this scale would probably contain many other species, including rarities hid­den within it.


Ecology

At the lagoon the tide was ebbing. Habitat types with shallow saline water and soil, such as lagoon, bay and estuary, are the most preferred by shore­birds for feeding, and this stage of the tidal cycle is their favou-rite time to do so.
There are several reasons. The sand or mud covered by the tide becomes softer, and areas now exposed or under a shallow depth of water are easier for the birds to dig for prey which live beneath it. The tide brings in algae, other aquatic vegetation and detritus of such material in the water, as it recedes much of this settles on the lagoon floor, and certain species of such fauna come up from the soil to feed on it. Ani­mal and vege­table food items, some of marine origin, including small fish, are taken from the water itself by the birds.

By far the majority of birds identified were, as seen above, Curlew Sand-pipers. In their wintering grounds they are known to feed chiefly on small, benthic (i.e. bottom-dwelling) invertebrates: worms, snails and other molluscs, shrimps and other crustaceans. The range of diet of the other shorebirds identified is very similar, with the addition mainly of insects and the larvae of these fauna.

The species of shorebird occupying the tide fringe and differing depths of water in this situ­ation varies according to several other factors, still mostly linked with 'food-partitioning': chiefly, length and structure of bill, methods of its use in feeding, and length of legs. We were un­able to focus on the feeding behaviour of the birds as we were too occu­pied with the count and also because of the distance.

This day the birds were all in the shallow water, gradually increasing in depth away from the shore. Among the species identified it was notable that all the Lesser Sand Plovers, too, were in water, which is unusual for them. The reason may have been richer feeding there or better secu-rity among the other birds.

It is possible that the population of one or more species of the benthic fauna and/or aquatic micro-flora at this site varies over a scale of days, with the co-relation of tidal and diurnal cycles, and this was a peak.


Studies of the fauna beneath the lagoon floor and the vegetable matter in the water of the lagoon will yield information useful for understanding the attraction of the site for shorebirds. This day, we could partly have examined these small fauna by scooping and washing some soil - but after the count U.H. and T.S. quickly turned to photography and U.S. continued to scan the site, as the birds were retreating with the water and the light was dimming.

We either know of, or satellite images show what appears to be, very similar habitat in the following locations (see map), listed from North to South: near Iluppai­kadavai on the coast c. 12 km to the north of Vidat-taltivu, across large areas by the coast between the latter and Tiruketis-waram c. 10 km south-west of it, around Erukkilampiddi bay c. 16 km to the north-west of this area, at Toddaveli near the far end of the bay, in the Vankalai Sanctuary to the south of that area and the Arippu area c. 14 km south of the last. Kora Kulam, a tank near the bay, offers such habitat when its water is at a cer­tain level.

Within the region, the presence of a very large number of shorebirds at a site one day and their complete absence the next has often been observed over the years. This proves that they flight in such numbers among these sites, and also possibly other sites elsewhere. They choose places which offer the best feeding at the time with adequate security.

In 1992 T.W. Hoffmann produced four maps for the census, as National Co-ordinator, detailing the richest waterbird regions in Sri Lanka:

Jaffna, Mannar, Puttalam and "Hambantota". It is notable that the Man­nar map indicates all these sites except Iluppaikadavai, beyond its borders. Since then, the armed conflict precluded visitors to this area until 2002 and its two extremes, Vidattaltivu and Arippu until 2010.


Distribution

In the 2006-7 migrant season "at least 90,000" shorebirds were recorded at the Toddaveli sand and mud flats, with the species composition similar to those at Vidattaltivu. Gatherings of several 1,000s of shorebirds have been recorded regularly at many locations within the large area of the Vankalai Sanctuary, some of these being of Black-tailed Godwit Limosa limosa in the shallows of the sea on either side of the Mannar Causeway.

Previously the two largest gathering of shorebirds recorded in Sri Lanka at one site were in the South-East and East. In Bundala Sanct­uary, at Malala Lewaya, "more than 100,000" were seen in the 2001-2 season; due to distance the only identification was that "a large number ... appeared" to be Little Stint. In the 2002-3 sea­son the "wader habitats around" Pottuvil held 80-100,000 waterbirds of whom the majority were shorebirds with a similar species composition as at Mannar.

The highest countrywide totals of shorebirds in the annual waterbird census since 1983 (with one year left out) have been c. 139,000 in 1989 and 132,000 in 2002. The highest total of all waterbirds has been c. 304,000 in 1989!
It is possible that during every Northern winter migrant season 100,000s of shorebirds arrive and stay in Sri Lanka, but are not recorded because the sites they occupy are not accessible to or not visited by observers. The sites described in the Mannar region and similar sites in the Jaffna Pen­insula, in the islands to its West and the lagoons to its South offer simi­lar, favourable habitat. Very large numbers of shorebirds are known to flight within these two regions, and may also fly along the c. 70 km coastline between them.

On the other hand, it is possible that in the 2009-10 season there has been an extraordinary influx to Sri Lanka. It is not yet known whether there has been a significant reduction of shorebirds in the Indian main-land this season. Generally, their numbers in South Asia are not well known because of the lack of adequate surveys.

It is in the Mannar and Jaffna regions that these birds are assumed to make landfall on arriving in Sri Lanka, at the terminus of the great Central-South Asian flyway, after moving through the two "sub-flyways" over the Western and Eastern coasts of India, respectively.

The breeding grounds of the species named range across Asia at latitudes from Arctic Siberia to North India with populations weighted heavily to­ward the former.

With this survey Vidattaltivu becomes one of the handful of integral sites in the world known to hold a million shorebirds at one time, and possibly the only one where such a number has been seen in one ground - as opposed to a high aerial - view. Delany has remarked that it "must be one of the most important shorebird sites (maybe even the most important) on the Central Asian Flyway."


Conservation

In 2008 Vankalai Sanctuary was declared by the State on information provided by the CBC, chiefly from the annual waterbird censuses. The information above makes it imperative that the Vidattaltivu wetland and the other sites listed above in Mannar be protected. Fortunately, a critical factor is favourable: human population at these is very sparse.

With the delay in the publication of the present issue of this jounal, we are able to note the fine response of the Department of Wildlife Conser-vation. About a week after our observation a team led by the Deputy Director, Development and Management, Mr Manjula Amararathna, visited the site.

He has proposed to the State, under a special programme, the status of Sanctuary for an area comprising a wide coastal strip from Vidattaltivu to Tiruketis­waram, the sea extending west from there and adjacent to the Vankalai Sanctuary until Erukkilam­piddi bay, then the bay and sand flats bordering it to its end beyond the Tod­daveli causeway, and an extension to the south-west also to include Kora Kulam. Although con­tiguous with the present Sanctuary the law requires that it first be declared separately.


Acknowledgment

The 2010 waterbird census in the Mannar region was possible in the pre-vailing security situation only by the co-operation of the armed forces. At the outset Commander H.S.K. Dissanayake of the Navy kindly pro-vided us with an escort. Petty Officer R.H.S. Ranaweera accom­panied, and courteously helped, us on land and sea. At Vidat­taltivu, the Officer-in-Charge, Lieutenant H.K.D. Randeniya of the Army kindly per­mitted us to walk on the lagoon shore and use the watch­towers. At the second of these Private J.K.D. Anura Shantha politely accommodated us.

References

Abeyratne, S. 2010. In: Ceylon Bird Club Notes January: 22.

Ceylon Bird Club Notes. 2002 to 2010. Reports on the Mannar region by numerous authors. (Those listed here have given reports of specific observations quoted above.)

Delany, S. 2010. Pers. comm. in two emails.

Delany, S. and Scott, D. 2006. Waterbird Population Estimates: Fourth Edition. Wageningen: Wetlands International.
Department of Sustainability, Environment, Water, Population and Com-munities [Australia]. 2010. http://www.environment.gov.au/cgi-bin/ sprat/public/publicspecies.pl?taxon_id=856.

Gunawardena, K. 2007. In: Ceylon Bird Club Notes February: 35.

Gunawardena, K. and Wikramanayake, T. 2007. In: Ceylon Bird Club Notes September: 184.

Henry, G.M. 1998. A Guide to the Birds of Sri Lanka Third edition. Kandy: K.V.G. de Silva and Sons and New Delhi: Oxford University Press.

Hoffmann, T.W. 1992. Detailed map of Mannar Wetland Sector with description of sites. In: Ceylon Bird Club Notes August: 99.

Hoffmann, T.W., Gunawardena, K., Sirivardana, U. and Senanayake T. 1983 to 2010. Reports of annual waterbird censuses in Sri Lanka, 1983 to 2010. In: Loris 1983 June 16,3 to 2010 June 25,5.

Phillips, W.W.A. 1973. Bird Migration in Relation to Ceylon. Parts I and II. Loris 1972 December 12,6: 284, 1973 June 13,1: 16.
Phillips, W.W.A. 1978. Annotated Checklist of the Birds of Ceylon (Sri Lanka): page v. Colombo: Wildlife and Nature Protection Society of Sri Lanka and Ceylon Bird Club.

Puttick, G.M. 1979. Foraging behaviour and activity budgets of Curlew Sandpipers. Ardea 67:111.

Seneviratne, S.C., Seneviratne, H. and Seneviratne, S. 2002. In: Ceylon Bird Club Notes January: 2.

WikiMapia. 2010. http://wikimapia.org/#lat=[y]&lon=[x]1&z=[v]&l=0 &m=s. Several settings of x, y and v were used relevant to sites named above in the Mannar region.