Yu-Seong Choi

Distribution of Waterbirds in Rice Fields and Their Use of Foraging Habitats

Abstract. Over the course of a year, rice fields display spatial and temporal differences according to farming management practices, providing a succession of habitats throughout the crop-growing cycle for various waterbird species. However, few studies have assessed the influence of the spatial and temporal differences produced by rice field farming management practices on waterbird species during a year. The present study investigated spatial and temporal patterns of species distribution and examined the factors that affect waterbird selection of foraging habitats in the rice fields located in the midwestern part of South Korea from April 2009 to March 2010 and from April 2011 to March 2012. Waterbird species represented strong seasonality and selectively used different field types at a fine spatial scale. The selection of field type depended more on field structures that were related to the vulnerability of prey items than on prey abundance in rice fields. Water level was an important factor that affected shorebird selection of foraging habitat, and they chose habitats with different water levels according to their body size. The density of rice plants was a critical factor affecting the selection of habitats by herons, because densely planted fields inhibited their access to food. The presence of rolled straw in rice fields affected the distribution of waterfowl. These results demonstrate that farming management practices, which determine prey accessibility, strongly affect the use of rice field habitats by waterbirds. Our knowledge of these relationships should be incorporated into conservation practices protecting the various waterbird species that use rice fields.

Patterns of Waterbirds Abundance and Habitat Use in Rice Fields

BACKGROUND: As natural wetlands are decreased by increment of human demand, the importance of rice fields as an alternative habitat for waterbirds is well documented. However, the relationship between waterbirds use and management practice of rice fields has not been fully understood. The present study attempted to understand the changes in temporal abundance of waterbirds and their preference for habitat types in rice fields all year round. METHODS AND RESULTS: Waterbirds census were conducted in rice fields around Asan bay in Korea during April 2009-March 2010 and April 2011-March 2012. In the bird counts, the locations of the observed birds on a 1/2,500 map were recorded along with the local habitat type (paddy, ditch, levee, road). Thirty five species of waterbirds recorded in the rice fields during the survey period and three major groups (shorebirds, herons, and waterfowls) were characterized according to season and micro-habitat use. Shorebirds visited a flooded paddy for feeding during their spring migration season (April-May), and herons used the rice field as feeding sites during their breeding periods (April-October). Most waterfowls were observed in a dry paddy to feed a fallen rice seed and stubs during the winter season (September-March). Waterbird groups selectively used micro-habitats in rice field. Shorebirds and waterfowls mainly preferred at rice paddies, while herons were attracted to most habitat types. CONCLUSION(S): Rice fields supported various waterbirds all year round and waterbird communities using the rice fields were dramatically changed according to seasonal change of rice field condition.

A Study of Feeding Methods in Five Species of Herons and Egrets in Korea

Feeding methods of five species of herons and egrets were studied in an agricultural landscape in Asan city, Chungcheongnam-do, Korea in 2006. Grey herons primarily hunted while standing, whereas great egrets fed while walking slowly. Two smaller species, little and cattle egrets, were active foragers, feeding both while walking quickly and walking slowly. Little egrets were the only species using the foot stirring method. The medium-sized heron, intermediate egrets, foraged mainly while walking slowly or leaning. For grey herons, great egrets and little egrets, the frequency of use of different feeding methods was different between habitats: these species used the leaning method more frequently in rice fields than in reservoirs and ditches. Also, most herons (all species other than great egrets) showed seasonal changes in their feeding methods that are related to changes in habitat condition.

Factors affecting feeding activity of grey herons in a reservoir during the breeding season

To examine factors affecting feeding efficiency of grey herons ( Ardea cinerea), the foraging behavior was studied at a reservoir in Asan city, Chungcheongnam-do, South Korea during the breeding seasons (from April to July) of 2006 and 2007. Four factors (age of foraging birds, time of day, breeding stage, and microhabitat type) were analyzed. Adults were more efficient foragers than recently fledged juveniles, and they had a higher success rate than juveniles. About half of the adults caught large prey, whereas most juveniles caught only small prey. Adult grey herons had different feeding efficiency according to the breeding stage. Pecking and capture rates were high during the late period (fledging stage), and biomass intake rates were high during the early (incubating stage) and late periods. However, time of day had no signifi cant effect on foraging activity of adult grey herons. Feeding activities of adult grey herons also showed significant varia tion among microhabitat types. Pecking and capture rates were higher in the submerged plants area, but capture success rate and biomass intake rate were not different according to microhabitat type.

Nestling diet of three sympatric egret species: rice fields support breeding egret populations in Korea

Abstract The diets of the Intermediate Egret Egretta intermedia, Little Egret E. garzetta, and Cattle Egret Bubulcus ibis were examined by analyzing nestling regurgitations collected during the breeding season in 2005 at a colony in Asan, South Korea. Intermediate Egret nestlings mainly fed on insects (86.7% of total prey items), but fish were the most important group by biomass (64.3% of total biomass). Little Egret nestlings fed mainly on insects and fishes (43.4% and 33.2% of total items, respectively), and fish contributed 64.2% to the total biomass consumed. Cattle Egret chicks were mainly fed invertebrate prey (96.5% of total items), such as insects and spiders, which comprised just 64.3% of the total biomass of their diet. Loaches and aquatic insect larvae (mainly Odonata and Coleoptera) comprised a large proportion of the nestling diet of the three egret species. This suggests that all species forage primarily in rice fields, which represented the most extensive habitat surrounding the breeding colony.

Some Aspects of Laying, Incubation and Hatching in the Great Reed-Warbler

During the breeding season of 1998, breeding ecology of the Great Reed-Warbler (Acrocephalus arundinaceus orientalis) was studied at Yangsoo-ri and Yongdam-ri of the Yangpyung-gun, Kyunggi province, Korea. Egg-weight (CV: 6.25) was more variable than either length or breadth, and breadth was the least variable of the measures. Significant variations in overall egg-weight occurred between clutches, and that more of the total variation in egg-weight and shape are due to inter-clutch variation as to intra-clutch variation when the data were pooled. The last egg tends to be larger than the remaining eggs in the clutch of the Great Reed-Warbler, suggesting the Great Reed-Warbler may adopt the brood-survival strategy. When method 3 was used, the most common incubation period is 12 days. In the Great Reed-Warbler, the length of the incubation period was related to clutch-size when method 1 (r