Difference in the frequency of foraging of shorebirds depending on prey density, biomass, and energy density in a key stopover site

Abstract

After the completion of the Saemangeum reclamation, the Geum Estuary has emerged as a key stopover site (staging site) for feeding and roosting of migratory shorebirds in South Korea. However, there has not yet been any quantitative study on carrying capacity of the Geum Estuary tidal flats. For this, we conducted a series of study related to the status of migratory shorebirds and carrying capacity of the Geum Estuary in 2017. To begin with, we monitored the species richness and maximum population size of shorebirds stopping over the Geum Estuary (Yubu Island and Seocheon) during high tide of the spring and fall. Also, we collected the coordinates of the feces of shorbirds in Yubu Island during low tide of the spring and fall. In order to estimate the availability of food resources, we surveyed the density, biomass, and energy density of benthic macro-invertebrates in Yubu Island tidal flat during the spring. As results, we found that there was a rapid population decline of shorebirds in the Geum Estuary between 2016 (189,872 inds., unpublished data) and 2017(99,237 inds.), although there was no significant difference of species richness of shorebirds. During the northward and southward migration of 2017, only 95,299 and 31,422 individuals stopped over the Geum Estuary, respectively. Such a year-to-year fluctuation of population size of shorebirds indicated that the Geum Estuary tidal flats are not stable to supportn carrying capacity of the Geum Estuary tidal flats. For this, we conducted a series of study related to the status of migratory shorebirds and carrying capacity of the Geum Estuary in 2017. To begin with, we monitored the species richness and maximum population size of shorebirds stopping over the Geum Estuary (Yubu Island and Seocheon) during high tide of the spring and fall. Also, we collected the coordinates of the feces of shorbirds in Yubu Island during low tide of the spring and fall. In order to estimate the availability of food resources, we surveyed the density, biomass, and energy density of benthic macro-invertebrates in Yubu Island tidal flat during the spring. As results, we found that there was a rapid population decline of shorebirds in the Geum Estuary between 2016 (189,872 inds., unpublished data) and 2017(99,237 inds.), although there was no significant difference of species richness of shorebirds. During the northward and southward migration of 2017, only 95,299 and 31,422 individuals stopped over the Geum Estuary, respectively. Such a year-to-year fluctuation of population size of shorebirds indicated that the Geum Estuary tidal flats are not stable to support