The Visitation Aspect of Great Crested Grebe (Podiceps cristatus) in the Long Period at Nakdong Estuary, Busan, Republic of Korea

Abstract

This study was conducted in order to analyze the long-term arrival pattern of the great crested grebe (Podiceps cristatus) in the Nakdong River estuary area, where undergoes rapid environmental changes, by studying the data of early 1990s (between May of 1989 and April of 1993) and the data of mid-2000s (between May of 2002 and April of 2006). The result of data analysis of 8 years showed that, of the total 2,873 members of the family Podicipedidae, there were 908 individuals (31.60%) of the great crested grebe (Podiceps cristatus) observed in the Nakdong River estuary area. The analysis of early 1990s and mid-2000s showed that, in terms of early 1990s, while a small number was observed in October, the number of birds arriving began to increase in November, with the highest number observed in December. In mid-2000s, the smallest number was observed in October, with the number of birds arriving increasing in November and the highest number observed in December. Monthly average number of individuals was approximately 1.7 times higher in 2000s than in 1990s. In terms of the number of individuals per month, there was no significant difference between the time period between November and March of early 1990s and mid-2000s (P<0.343). The average number of individuals per region of the great crested grebe in mid-2000s (between May of 2002 and April of 2006) was 38.53 individuals, and there was no significant regional difference (P<0.075), with 5.00 individuals in Daema-deung (DMD), 6.00 individuals in Jangja, Shinja-do (JJ.SJD), 4.67 individuals in Saja, Doyo-deung (SJ.DY), 6.00 individuals in lower Ulsuk-do (LUD) and 129.50 individuals in Ulsuk-do (USD). Since the great cormorant, a diving bird species which feeds on fish, use lower Ulsuk-do (LUD) and Saja, Doyo-deung (SJ.DY) as foraging and resting ground, it is assessed that the great crested grebe, which is smaller than the great cormorant, use Ulsuk-do, the region right below the estuary dam, as their habitat.