Waterfowl and their Habitats in the Gulf of Thailand
Written:Philip D.Round
First published in BCST's Bulletin(Vol.18 No.4 April 2001)
All Photo:Porpol Nontapa

Abstract 
        Both in terms of total numbers of waterfowl, and range of species represented, the Inner Gulf of Thailand, in the vicinity of Bangkok, is the single most important site for migratory waterfowl, especially waders and terns, in the entire country and is a wetland of international importance. The estimated numbers of waterfowl using the site per year are in the region of 150,000- 300,000. Counts and projected populations for 102 species are presented. These include 16 species which are globally threatened or near threatened. And 17 species for which the gulf regularly supports more than 1 % of the flyway population. 
        According to a variety of criteria, the inner gulf is therefor a wetland of international importance. It is also of great socio-economic value supporting inshore fisheries and sail farms, and is of critical importance as a buffer protecting Bangkok from marine encroachment. In spite of this, its importance remains almost totally unrecognized by government agencies, and changing land-use, especially industrialization, threatens its important functions. It is recommended that the site be considered for inclusion as a wetland of international importance under the Ramsar Convention. Zoning measures should be introduced to conserve its key values. The most important areas for migratory and nesting shorebirds are identified.

Introduction 
          Five major rivers enter the Gulf of Thailand between Chonburi in the east, to Phetchaburi in the west These are the Bang Pakong, Chao Phraya, Tachin, Mae Klong and Phetchaburi Rivers. Silty deposits spreading from the deltaic fans of these rivers have developed into extensive mudflats and associated mangroves which sustain large populations of both humans and wildlife. 
          Though most mangroves have been cut or otherwise degraded over the past hundred years, to be replaced by an extensive belt of prawn-ponds, salt-pans, urban and industrial sprawl, mudflats and sand flats still remain. In addition, extensive areas of secondary mangrove scrub remain and in sonic areas are recolonizing abandoned ponds. 
           Intertidal mudflats are important feeding areas for resident and migratory waterfowl and other waterbirds, and sustain important inshore fisheries, which the prawn- farms, salt-pands and remaining mangroves continue to be important as feeding, roosting and in some cases breeding areas for large numbers of waterfowl. In the past, these intertidal and brackish habitats formed a continuum with inshore fresh-water habitats, grading into them. Older Bangkok residents can still remember (e.g.) mudskippers and Collared Kingfishers (Todiramphus chloris) in the city precincts. This continuum is less perceptible and much more interrupted now by the urbanized belt effectively separating the coastal habitats from the rice-paddy hinterland. 
           In this paper I have chiefly confined myself to the immediate coast, encompassing only intertidal and brackishwater habitats, though I recognize that there is still much interchange of bird populations between the intertidal and brackish water zones in the hinterland on the other. 
           The importance of the inner gulf for waterbirds and other wildlife was recognized as long ago as the first few years of the Twentieth Century. Gyldenstolpe (1913) recorded “great flocks” of Spot-billed Pelicans in the gulf during April and May; Gairdner (1914) found otters around the lower Mae Klong; Williarnson(1918) listed some waders, apparently including a concentration of Great Knots. Herbert (1926) was aware of a colony of large nesting waterbirds, including Black- headed Ibises, near Samut Sakhon. Later, Jorgensen(1949) discussed the many wader specimen, collected mainly in the gulf by C.J. Aagaard before 1930. In the past couple of decades, there has been more work on shorebirds in the gulf, including a limited amount of banding (Melville 1982; Melville and round. 1982). In 1984, the first ever major concentration or the globally nearthreatened Asian Dowitcher (ca. 400+) was found at Samut Sakhon(Lekagul, Round and Komolphalin, 1985; Round, 1985). This dowitcher discovery in the Gulf of Thailand was followed shortly afterwards by the discovery of an even larger number in the newly discovered wintering area for this species in Sumatra
(Silvius et al., 1986). Contemporaneously, work carried out by Interwader at several sites along the Thai coast, included an aerial survey of both coasts of the entire peninsular coast and the inner gulf (Parish and Wells, 1984; Sharks, 1985). Since that time, work elsewhere, in Pattani Bay, S. Thailand (Swennen et at. 1986; Ruttanadakul and Ardseungnero, 1986) and throughout East Asia and South-east Asia has greatly improved our understanding of shorebird numbers and distribution (Wells and Mundkur, 1995). 
           The inner gulf of Thailand was one of 14 coastal sites in Thailand listed by Scott(1989) as being of either national or international importance. 
           Although our knowledge has increased, the threats to shorebirds have grown even more, especially through rampant land speculation and pressure for land reclamation. Most such reclamation around Bangkok has taken place in a piecemeal fasion, but some Thai government agencies (e.g., Department of Fisheries) have been in the forefront of efforts to promote reclamation of the coastal zone so as to establish onshore fisheries-based in- dustries (Tunhikorn and Round, 1995). Erftemeijer and iugmongkol (1999) provide a summary of these and other threats to the gulf. 
         Legislation to conserve wetlands (e.g., through promoting sustained multiple use, such as through Zoning) has lagged far behind development. Thailand’s (1998) ratification of the Ramsar convention is barely known outside of a small coterie of government officials, and in any case is no more than a token gesture since the site nominated (Khuan Khisian, a tiny fragment of Thala Noi Non-Hunting area) is an island knoll, and in no sense even qualifies as a wetland. No efforts have yet been made to frame indigenous Thai wetland legislation to accord with the newly drafted wetlands policy. 
           The recognition of the importance of the inner Thai gulf, combined with perception of the severity of the threats to its integrity, led BCST to invite Wetlands International to participate in monitoring shorebirds there to provide an update on our knowledge. Under this three years, which covered large segments of the inner gulf, both by boat and from the land, were completed during February-April 1999. The results of these surveys, and other observer’s counts covering the same period, are summarized in Erftemeijer and Jugmongkol(1999). BCST has since mounted one other coordinated count which has extended coverage of the midwinter period.

Results 
         The definition of waterfowl is that used in Rose and Scott(1997) and implies all bird species which are ecologically dependent on wetlands. There are some anomalies, however: some kingfishers. birds of prey, many warblers, etc. are also dependent on wetlands though are excluded from the definition the grounds that most members of these families are not. Waterfowl are essentially larger waterbirds and the groups of most significance to Thailand and the Inner Gulf are ducks, waders, terns, herons and cormorants. Waders (families Scolopacidae and Charadriidae) are sometimes referred to as shorebirds. Certain families or species which are primarily or exclusively fresh-water (e.g. jacacanas, paintedsnipe) are excluded from this analysis, as are rails, most of which are secretive and difficult to count, and for which there is relatively little information. 
         Populations of waterfowl in the gulf constitute two great seasonal assemblages. Firstly, there are resident birds, which remain in the area all year-round and which nest in the area. This group includes most herons, cormorants. Then there are the migratory birds, most of which in terms of numbers of species and individuals are shorebirds and terns. Most such species nest either on arctic tundra, boreal taiga, or in the plateaus and steppes of Central Asia, and migrate to tropical latitudes during the palearctic winter. It is usual to divide populations of migratory waterfowl into “flyways which link their breeding and wintering areas. Within Asia, ore such flyway extends into India; another the “East Asian flyway” extends into SE Asia. Many species of shorebirds on the East Asian flyway winter in Thailand and seldom stray much further south (e.g., most ducks), many waders migrate even further, reaching the coastlines of the Indonesian archipelago and even Australia. The largest numbers of a great many waders are therefore found during spring and autumn passage seasons rather than during the midwinter. 
          A total of 102 species of waterfowl (including 7 ducks, 50 waders, 18 terns and gulls, 27 miscellaneous other, including cormorants, storks and herons) are considered to occur in the brackish and intertidal habitats along the inner gulf. 
          This total includes 8 species which are globally threatened and another 8 species which are nearthreatened. While a few of these are vagrants or recorded only occasionally, the great majority are regular annual winter visitors or passage migrants, occurring in significant numbers. Seventeen species, mainly herons or cormorants, but including one duck, four waders and a tern are at least partly represented by populations which are resident and still breed locally around the gulf. 
          Under the Ramsar Convention, criterion 3(3) states that a wetland is of international importance if it supports more than 1% of the individuals in a population of one species or subspecies of waterfowl. The inner gulf certainly supports more than 1% of the flyway population for at least 17 species of waterfowl, while for a further ten species, the numbers are within or close to the likely 1% rage. 
          Erftenmeijer and Jugmongkol (1999) made a total count of 18,692 shorebirds and 5,801 other waterfowl during the northward (spring) migration in the Inner Gulf, 10-11 april 1999. They estimated that for waders alone, the total number of birds present in the inner gulf per year is 100,000- 135,000 birds. In fact, the true numbers could be significantly higher than this, since even in the most complete count, only part of the total area was covered. A midwinter count implemented by BCST in just the western sector of the gulf (Samut Sakhon-
Phetchahuri) recorded 16,915 waders, only slightly fewer than Erftemeijer and Jugmongkol’s (1999) spring passage total for most of the gulf, and at a time of year when total numbers should be very much lower than for spring passage. 
          In addition, neither of the above totals includes the other waterfowl (terns, herons, duck, etc.) BCST in January 2000 recorded 14,205 “other waterfowl” compared with for 10,678 for Erftemeijer and Jugrnongkol in spring. When these are taken into account, the true numbers of waterfowl using the inner gulf in any one year are likely to be in the region of perhaps 300,000 birds. 
          I discuss the significance of these findings with regard to specific group below.

Shorebirds 
           Shorebirds, most of which are migrants, constitute the major assemblage of birds in the gulf. Major waves of northward-bound migrants move through the gulf in spring. Among the most numerous species at this time are Lesser Sand Plover, Pacific Golden Plover, Curlew Sandpiper, Black-tailed Godwit and Common Redshank. The occurrence of large numbers (600+) globally nearthreatened Asian Dowitchers at this time is also of particular significance. Autumn migration of most waders is more protracted, and total numbers at any one time usually lower. Numbers of many species in midwinter are much less than in spring and autumn. Black- winged Stilt is one of the most numerous waders through out the year, with the largest winter count in excess of 1800. An undetermined number breeds. 
Terns and Gulls 
          The presence of large numbers of Brown-headed Gulls (5000+) is well known and is a major attraction for local visitors to the military convalescent center at Bang Pu. It is less well known that the gulls are scattered throughout the whole coastline, though the largest numbers probably roost offshore or on ponds in the region of the Chao Phraya and Tachin river mouths. Rose and Scott
(l997) estimate the world population of brown-headed gull at only 100,000 birds, so that the inner gulf of Thailand may support up to 5% of the known world population. Large numbers of terns (Mainly Whiskered Terns) are present in the gulf throughout the winter. Individual counts of 5000-6000 Whiskered Terns have been made at two sites, as birds flight out offshore in the early evening, presumably to roost on offshore structures such as fish-traps. The large of Common Terns(1500) have been recorded in early autumn: midwinter numbers air much lower suggesting that the majority of bird seen in the gulf are merely passage migrants. An undetermined number of Little Terns nests in the gulf, breeding birds having been found around Samut Sakhon and Phetchaburi provinces, at least.