Patterning habitat preference of avifaunal assemblage on the Nakdong River estuary (South Korea) using self-organizing map

A comprehensive monitoring of the avifaunal assemblage to observe patterning changes was attempted for an estuarine system in South Korea. The current work identifies the importance of conserving habitat for migratory birds especially in the studied Nakdong River estuary. This estuarine system has been recognized as one of the most important stopover sites on the East Asia–Australasian Flyway, and supports a high level of biodiversity. The installation of an estuarine barrage in 1987 resulted in the habitat being partitioned into freshwater and brackish areas; however, there has been no systematic monitoring throughout the estuary. In the original survey program, the entire system (ca. 100 km2) was divided into eight sites and monthly or biweekly monitoring was implemented for the 3 years from April 2003 to March 2006. 227 species of birds were observed, with the dominant species being mallard (Anas platyrhynchos Linnaeus) (relative abundance, RA, 17.2%). Assemblage parameters showed avifauna biodiversity possessed a strong seasonality with some species groups dominating the estuary. A non-linear patterning self-organizing map (SOM) algorithm was applied to the avifaunal data set to identify patterns in avifaunal distribution. The trained SOM model (quantization error, 3.375; topographic error, 0.000) clearly classified the bird data set into two clusters. These clusters could be characterized by two factors: i.e., seasonal distribution of avifaunal assemblage and/or habitat properties. High dissimilarity between clusters was due to seasonality, while the brackish area (i.e., the cluster 1) was mostly occupied by cold season data while the reverse was true for cluster 2. By comparing bird data from the sub-zones, it was found that the center of the brackish area had a mixed pattern of bird distribution, which implied this area could be more important in terms of habitat preference with respect to migratory bird distribution. From the results, it is strongly suggested that a strict management strategy for the estuarine area to conserve the avifauna throughout the migratory flyway be prepared. The strategy could be seasonally and species specific.