Heavy Metal Level In The Ardeid Food And Their Effects On Their Eggs

The egg and food samples were collected during the breeding period of little egrets(Egretta garzetta), black-crown night herons(Nycticorax nycticorax), Chinese pond egrets(Ardeolaa bacchus) and cattle egrets(Bubulcus ibis) from the Jiyu islet in Xiamen Egret Natural Reserve. The food habit of four species of ardeids was analyzed. The content of the heavy metal levels, lead (Pb), cadmium (Cd), copper (Cu) and zinc (Zn) in the egg and food samples were measured using atomic absorbing spectrometry (AAS). The distributions of the four heavy meatal in the egg and food samples, and the relationships between them were also analyzed. We aim at discussing the ardeid egg as a biomonitor for heavy metal contamination in the environment and gaining some basic data for the future study of the heavy metal damage on the reproduction and development of bird.The nestlings in four species of egrets and herons all preyed on small animals. Night herons mainly prey on shrimp, fish, and frog. The fish of Mugilidae and Cyprinidae and the shrimp were the most food of little egret. The fish of Mugilidae and Cyprinidae and the insect of Coleoptera larve and Odonada nymph were the most food of Chinese pond egrets. The food of cattle egret was mostly locust, cricket, spider and frog.The determined heavy metal (Cu,Zn,Pb,Cd) of the food samples in the four species of egrets nestlings were Zn>Cu>Pb>Cd, in which the Zn>Pb>Cd>Pb was found in spider, locust, and shrimp. The content of Cu was higher in spider, insect, and shrimp and lowest in fish. The content of Zn was higher in fish and earthworm and lowest in insect. The content of Pb was highest in fish and lowest in shrimp. The content of Cd was highest in spider and lowest in fish. The heavy metal content was higher in seafish than in freshwater fish. The heavy metal content was highest in locust.The mean egg weight in four species of egret or heron was black-crown night herons > cattle egrets > little egrets > Chinese pond egrets, in which the egg weight was the black-crown night herons,cattle egrets > little egrets > Chinese pond egrets (P<0.05) ,but no difference was found between the egg weight of black-crown night herons and cattle egrets (P>0.05). The mean egg length was black-crown night herons > cattle egrets > little egrets > Chinese pond egrets, in which the mean egg length was black-crown night heron > little egrets > Chinese pond egrets, cattle heron>Chinese pond egrets (P<0.05) ,but no differences between cattle egrets and black-crown herons or between cattle egrets and little egrets (P>0.05). For the width of eggs, there are no differences among the four egrets (P>0.05).The distribution of heavy metals in the egg was Zn>Cu> Cd> Pb in eggshell, Zn>Cu>Pb>Cd in the egg content, egg albumen, egg yolk (P<0.05). The heavy metals levels in the eggshells were significantly higher than other sections of egg (P< 0.05). The Cu level was little egrets lower than Chinese pond egrets, cattle egrets and black-crown night herons in the egg content (P<0.05), cattle egrets > Chinese pond egrets > black-crown night herons > little egrets in the eggshell (P<0.05), and cattle egrets > Chinese pond egrets > black-crown night herons and little egrets in the egg yolk (P<0.05). The Zn level was little egrets higher than cattle egrets in the eggshell (P<0.05), black-crown night herons > little egrets > cattle egrets or Chinese pond egrets in the egg yolk (P<0.05), and black-crown night herons > little egrets, Chinese pond egrets or cattle egrets in the egg content (P<0.05). The differences of Pb level was not significant among eggshell, egg content, egg albumen in the four species of egrets or herons, but significant in their egg yolk, in which black-crown night herons or cattle egrets > little egrets or Chinese pond egrets (P<0.05). The differences of Cd level was significant in the eggshell, in which cattle egrets > black-crown night herons or Chinese pond egrets or little egrets (P<0.05).Our results showed that heavy metals mainly concentrated in the eggshell of ardeids and that the Pb,Cd level in the egg content were higher in Xiamen than other places which indicated that the Pb,Cd pollution was more severe in Xiamen ocean. Our results found that different species of ardeids had different diets that contained different level of heavy metals and also found that there was an interspecific difference of Cu level in the eggshell or egg yolk, and Zn level in egg yolk and Cd level in eggshell. Therefore, the differences of food composition among ardeids could influence the heavy metal level in their eggs that indicated the ardeid egg was a good indicator for estimating the environmental pollution of heavy metal.