The Feeding Ecology, Requirements and Distribution of Baikal Teal Anas Formosa in the Republic of Korea

The feeding ecology, requirements and distribution of Baikal Teal Anas formosa in the Republic of Korea G.A. ALLPORT, C.M. POOLE, E.M. PARK, S.R. JO and M.I. ELDRIDGE An overwintering population of up to 20,000 Baikal Teal was found at the Ch ’unam reservoirs in the Republic o f Korea in 1984. The first detailed studies at the site were undertaken in December 1989 and January 1990; it comprises three water storage reservoirs, Sannam (75 ha), Ch ’unsan (307 ha) and Tongp’an (50 ha), located on the south side o f the Nakdong river valley, South Kyongsang Province (35°18'N, 128°14'E), and holds 18-20,000 Teal in large monospecific flocks. Sixty-two percent of the birds were males in full breeding plumage, and 17% were paired. Displaying Teal were noted only twice. Feeding was predominately nocturnal, the lakes being used as a diurnal roost. All birds formed into one flock at dusk and thence flew up to 7 km to feed on agricultural land. Observations andfaecal analysis showed that the birds were feeding exclusively on rice from paddy fields which had been harvested by machine in the previous autumn and were completely dry. Seventy-three percent o f harvested rice fields were suitable fo r Teal to feed on, the rest being cleared (9%), burnt (7%) or ploughed (11%). Occasional birdsfed during the day on the reservoirs by either dabbling orfilter feeding in melt water lying on top o f the ice after an overnight freeze. Estimates of energy requirements and food intake suggest that the population requires 111,600-225,000 kg o f rice ears for a 90 day season (1.8 million bird days) and that therefore 3392-13,636 ha o f suitable harvested rice fields are needed to support them throughout the winter, or more if other granivores are competing. There are 3478 ha o f suitable rice fields within 8 km o f the reservoir. The birds are threatened by disturbance from fishermen, hunters, visiting tourists and local domestic traffic. Overhead power cables may cause significant mortality. None o f these is a major threat at present but the exclusive, monospecific nature o f Baikal Teal makes them vulnerable to particular hunting techniques or chance events such as disease. A survey o f 12 other potential sites in the southern part of the Korean peninsularfound only three suitable, one of which held 200 Baikal Teal. La Touche (1925-34) described Baikal Teal present at the site from late November until Anas formosa as “the commonest duck in early March. north-east Asia”. This species was formerly The reasons for the general decline are un abundant throughout southeast China and Ja known. In Japan, hunting pressure may have pan; groups of 10,000 birds were not uncom been a factor but, as little was known of the mon and there were occasional flocks of 100,000 species’ wintering ecology, it was difficult to strong (Austin & Kuroda 1953). A dramatic infer its requirements. As a result it was pro decline in numbers was noted during the late posed that a short study of the birds at Ch’unam 1970s with fewer than 10,000 birds in the whole be undertaken to provide background informa of Japan in 1980 (Brazil 1991). In the light of tion for future conservation proposals. this, the discovery of a flock of5000 birds at the The aims of this study at Ch’unam were to Ch’unam reservoirs in the Republic of Korea in establish baseline data on the ecological re February 1984 (Won 1988) was of great signifi quirements of Baikal Teal and, if possible, to cance; the duck had only been noted previously assess the age structure of the population. The as a passage migrant in the republic (Gore & results of the work have been incorporated Won 1971). Numbers at Ch’unam varied over directly into Conservation Action Plans for both the following six winters but reached 20,000 the species (Poole in press) and the site (Poole birds at times, which represented over 80% of et al. 1990). An attempt was also made to locate the known world population. The birds were other key areas for Baikal Teal in the southern 98 WilJfowl 42 (1991): 98-107 Baikal Teal in Korea 99 Seoul Agricultural land Foraging sites Marshland Urban area Ch'unsan Lake T rack ■Tongp'an ' Lake \ \ JIN YOUNG Figure 1. The location of the Ch’unam reservoirs in the southeast of the Republic of Korea, and the distribution of agricultural land in the vicinity. The location of Baikal Teal feeding sites are marked "X". part of the Republic of Korea. voirs, Sannam (75 ha), Ch’unsan (307 ha) and An initial visit was made to Ch’unam by Tongp’an (50 ha) located on the south side of C.M.P., M.I.E. and E.M.P. on 14-16 December the Nakdong river valley (35°18'N, 128°14'E) 1989. The main fieldwork at the reservoirs took 14 km NNE of Masan, Uichang County, South place from 5-16 January 1990 and the survey of Kyongsang Province (Scott 1989) (Fig. 1). potential sites was completed on 18 January The reservoirs lie in an area of flat agricul 1990. tural land relieved by afforested high ground to the northwest and, more remotely, to the south and east. All of the low ground has been devel Study site oped for agriculture, the land-use in winter being a patchwork of harvested paddy rice, The site comprises three water storage reser young barley, plough and occasional crops such 100 G. A. Allport, C. M. Poole, E. M. Park, S. R. Jo and M. I. Eldridge as cabbages. Some areas are being covered by and daily temperature. Estimates of the diges large plastic greenhouses in which cut flowers tive efficiency and energy content of the food and vegetables are grown. Over the last five were determined from the literature and an years, barley has decreased in popularity but the estimate of daily intake computed. The avail use of greenhouses has increased markedly (H. S. ability of suitable feeding habitat was outlined Noh pers. comm. 1990) although rice still pre by surveying the land-use of the hinterland: 100 dominates and is usually harvested by a ma points located at random in the cultivated areas chine which casts the cut heads and straw in were visited and the land-use recorded. Details separate rows in the field (the structure of a rice of the extent of flat agricultural land were deter plant is shown in Appendix 1). The waste is mined in radial distance classes from the roost normally left on the field but is sometimes using large-scale maps. Notes were taken of all cleared and gathered, burnt or ploughed-in. The apparent sources of disturbance. locality is heavily populated, the edges of the valley and occasional low hills being centres for Age and sex structure human habitation. It has been suggested that first-winter birds, particularly males, may show unmoulted juve Methods nile feathers in the plumage of face or body. Captive birds complete a protracted moult by Habitat and behaviour December but wild birds might lag behind be cause of the poorer quality of their diet (N. Initial observations concentrated on simple fa Jarrett pers. comm. 1989). Male Baikal Teal miliarisation with the birds’ habits. Further ob attain full breeding plumage by abrasion of the servations were maintained with the objectives tips of their head and breast feathers, so the of determining their diurnal rhythm - notes were plumage condition of males was recorded to taken on the behaviour of the birds throughout give an indication as to the stage that birds had the day over the first three days of fieldwork and reached in the annual sexual cycle. Any display their daytime flight activity budget. The propor activity was noted. tion of the flock in flight was recorded at five A transect was taken through flocks of Teal minute intervals during daylight hours and the when at rest. This was done by fixing a tel mean value was used to determine the time escope on a distant point and then drawing an spent in flight during the day. These data were imaginary straight line to the observer. The age used in the calculation of the birds’ energy and sex of each bird on the line was recorded requirements. where possible; indeterminate individuals were recorded separately. The frequency of pair bond Food and feeding ing was determined by randomly selecting indi viduals from the flock and recording their sexual In the first instance, the birds were observed status by observing their relationships with ad closely whilst on the reservoirs and any feeding jacent individuals. activity noted. Attempts were made to follow flocks leaving the roost in order to locate birds Surveys of other sites feeding in the surrounding agricultural land. Notes were taken on the choice of habitat and Based on the results of the ecological investiga feeding techniques. tions at Ch’unam, predictions were made as to Faeces were collected and examined using a the requirements of wintering Baikal Teal. Suit 20-100x microscope. Ten subsamples were able sites where these requirements might be taken from each faecal pellet and spread onto a fulfilled were identified from maps and from a slide. At 100 random locations on each slide, the literature review: 12 sites were visited. food was identified. Areas under power lines were searched for dead birds in order to exam ine their gut contents.

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