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61 eggs of night heron (Nycticorax nycticorax) were collected in 2000 in Yuantouzhu of Tai lake, China. The breeding birds were divided into three groups by age, namely two, three, four years. The residues of 15 polychlorinated biphenyl congeners in eggs were studied. 15 congeners were found in all egg samples, and PCB118 at the highest level, PCB87, PCB101 and PCB153 at second levels. Total residues of the 4 congeners occupied about 75%-85% of sum 15 congeners residues found in eggs. It was obviously that residues of congeners containing 5-6 chlorine atoms were more than others in eggs. Residues of PCBs in eggs increased with age of breeding birds. The total PCBs concentration in eggs of four years group were higher than that of three years group, two years group by 47.5% and 60.9% respectively. Different from the result of the similar studies in European countries, USA and Japan: the residue of PCB153 is the highest, it was found that in this study the residue of PCB118 is the highest in eggs, which is about 30% of the total PCBs residues, while the PCB153 17% only.

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.