Availability of food sources in wetland ecosystem as one of the driving factors influencing the migrating pattern of water-birds have rarely been studied even though the global conservation status has improved. Purple Heron (Ardea purpurea L.) was classified as endangered to vulnerable and currently, as least concern. They are a non-breeding visitor in the north and northeastern Thailand, and has been observed at Bung Khong Long Non-Hunting area, a Ramsar site in Thailand. A maximum of 20 individuals were observed during the migratory season 2003/2004, which decreased to around 6 individuals between 2009/10 and 2010/11. Food availability for the Purple Heron was hypothesized to be affected by local fishing activities. Thus, fish and other possible food sources were sampled at six stations in the lake based on the feeding route of Purple Heron. Food sources were compared with the fish-caught by local-fishermen per day. Fishing activities (gears and frequency) were also investigated. The number of Purple Heron observed was obtained from the Department of National Parks, Wildlife and Plant Conservation, Bangkok and field observation during 2009/10 and 2010/11 migratory season.
Results/Conclusions
The migratory season was divided to early (EP), middle (MP), and late period (LP). The size and type of prey appeared to be the priority preference for Purple Heron. Seven out of 23 species of fish of medium size (5-15 cm) commonly fed on by Purple Heron, seemed to be the common fish caught by local fishermen. The number of the seven fish species of medium size frequently preyed on by Purple Heron was significantly higher in 2010/11 compared to 2009/10 migratory season (p = 0.003). However, amount of fish biomass appeared to be key driving factor for the Purple Herons than the number of fish. ANOVA on ranks showed significant difference in biomass of the seven fish species among periods with the highest in EP (p = 0.002) and decreased in LP. Fish caught by local fishermen from the seven species averaged 66,707 g m-2 day-1 whereas fish biomass available for Purple Herons averaged 606.08 g m-2 day-1, 256.75 g m-2 day-1, and 343.37 g m-2 day-1 in EP, MP, LP, respectively. Local fishing activities including fishing frequency and equipment used may have influenced foraging behavior of Purple Herons leading to shifting in feeding area.