[Egretta garzetta as a bioindicator of environmental pollution in Tai Lake region]

There were four species of Ardeidae in Tai Lake. The dominant vegetations in the habitat were Pinus massoniana, Cinnamomum hupehanum, Quercus acutissema, Ulmus prmila and Myrica rubra, which were suitable for Egretta garzetta to make nests. The area of the habitat was about 7 hm2, where there were totally 4200 Egretta garzetta nests with the density of 0.38 nest per tree in average. Studies on Egretta garzetta breeding ecology showed that the incubating time was 19-21 days, the average egg weight was 23.9 +/- 4.0 g(n = 41), and the average egg size was 44.5 +/- 4.1 mm x 32.6 +/- 4.9 mm(n = 41). The mean clutch size and brood size were 5.02(2-8) and 3.86(2-7), respectively, and the hatching rate was 84.25%. The measurements of Egretta garzetta nestling tarsus did not show any asymmetry (P > 0.05). Egretta garzetta fed mainly on small fish and shrimps in Tai Lake. The analysis results of Tai Lake samples showed that the pollutants including HCH, HCB, cyclodience, DDTs (DDT, DDE and DDD), PCBs, Cr, Hg and Pb in Egretta garzetta eggs were detected except Cd, and these pollutants accumulated through prey chain from sediments and preys to nestlings. Comparing samples from Tai Lake and those from Poyang Lake as relatively unpolluted area, only the concentration of DDTs residues was higher than 2 micrograms.g-1 in both lakes, and the other residues from Tai Lake like organochlorine insecticides, PCBs and heavy metals were all lower than those from Poyang Lake, and did not affect the development and breeding success of Egretta garzetta at present.