Food Supply of Purple Heron Disturbed by Local Fishing in Bung Khong Long Lake, Thailand

Abstract

Abundant wetlands are generally considered providing the fundamental niche to multi- diet feeders like Purple Heron (Ardea purpurea L) whereas the realized niche may be over-looked. This study hypothesized that the fluctuation of observed number of A. purpurea at Bung Khong Long Lake (Ramsar Site) has influenced by local fishing since the maximum number was observed decreasing to 6 individuals between 2009/ 10 and 2010/ 11 even though the status is least concern for the country. Due to its feeding behavior on not specific preys, all possible food sources was sampled following the feeding route of Purple Heron and then was compared with fish-caught by local fishing per day, as well as observed fishing activities to cross check with feeding time of Purple Heron. Field investigation was conducted in early (EP), middle (MP), and late (LP) period of migratory season 2009/ 10 and 2010/ 11 and cross check with the official recorded number of Purple Heron obtained from the Department of National Parks, Wildlife and Plant Conservation, Bangkok. Size and type of preys (seven fish species; medium size ~5- 15 cm) appeared to be the priority preference for Purple Heron’s feeding that was sampled higher in 2010/11 compared to 2009/10 migratory season (p = 0.003) and also seemed to be the common fish caught by local anglers. In addition, fish biomass has more or less influenced on the frequency of feeding rather than the number of fish and it showed significant highest in EP (p = 0.002) and less in LP as well as higher observed-number of Purple Heron in EP than LP. Based on daily required 200g/ day/individual, all food sources (mainly fish) sampling in the field insufficiently played a role as the hypothesized-realized niche for the maximum number of A. purpurea (606.08 g m-2 day-1; EP, 256.75 g m-2 day-1; MP, and 343.37 g m-2 day-1 ; LP, respectively). Whereas, fish caught on the seven species by local anglers resulted around 66,707 g m 2 day-1, which is higher than the hypothesized-realized niche that might push the birds to move out and shift to the better foraging places.