Diet of yellow bitterns (Ixobrychus sinensis) during the breeding season in South Korea

Yellow bitterns (Ixobrychus sinensis) are a small wetland bird common to Asian countries including South Korea, Japan,and China. The aim of this study is to describe diet of yellow bitterns during the breeding season in artificial wetland ofnortheastern South Korea between May to August 1999-2001. For the purposes of this paper, we observe the frequencyof nest visiting by parents during the chick rearing period. A total of 98 boluses regurgitated by 52 chicks aged 1 day to11 days after hatching form the sample and are shown to contain 323 food items. A bolus contained mean 3.8 items andweighs 0.2 g to 7.7 g. The most regularly occurring food items recorded are fish (63%) and insets (33%). In terms of fish,top mouth minnows (Pseudorasbora parva) and crucian carps (Carassius auratus) are frequently observed. In terms ofinsects, there are mosquitoes (Diptera), instars of dragonfly (Libelluidae), damselflies (Coenagrinonidae) and water bugs(Diplonychus japonicus). Yellow bitterns were also shown to feed on bull frogs (Rana catesbeiana), shrimp (Palaemonidae),and spiders (Araneae). The size of fish in a bolus ranged from 15.56 mm to 93.73 mm (mean, 37.08 mm). The amountof food can be observed to increase with the age of chicks (r = 0.279, P = 0.025, N = 64) but parents did not provide largerfish as chicks grew. Parent birds visited nests more frequently when they have a larger brood (F1,21 = 14.529, P = 0.001). Ourresults suggest that fish is the most important prey during the breeding season and that age of chicks is related to amountof diet in yellow bitterns.