Primary Studies On The Breeding Biology Of Some Species Of Egrets In Xiamen Egret Natural Reserve, Jiju Islet

From 2000 to 2001. research on the egrets mixed population in XiamenEgret Natural Reserve found that the Reserve and its extending areaprovided the population fitting conditions through winter. The dominatingcomponent is little egret (Elpetta garzetta) and there were some large egret(Egretta alba), cattle egret (Bubulcus ibis) and few chinese egret (Egrttaeulophotes). The movement of egrets in every day ptesented regularity Thenumber of egrets in 2000 was 5600 to 6300 and their habitat was in theDatuyu islet. In 2001, the number was about 3200 and the habitat was in theJiyu islet.The egrets population started breeding from Match to April. Thechiefly breeding place was in Jiyu in 2001, including 5032 little egrets, 4694chinese pond herons (Ardeola bacchus), 1692 black-crowned night herons(Nycticorax nycticorax) and 460 cattle egrets. The four species had a trendto group in each species respectively. In addition, the distributing pattemwas related with the time of egrets starting their breeding and with thebehavior of occupying the space prepared for nest.From March to July in 2000, research on the breeding biology of thelittle egret and pond heron was made in the Jiyu islet. The two species beganto group, select nest locality and build nest from mid-February tomid-Maxch. And then they started to lay eggs and incubated. In themid-April the nestlings were hatched out. The mean clutch size in little egretwas 4.43±0.68(SD), incubation period 23.2±1.4 days, incubation rate88.50%, mean number of the nestlings was 3.8±0.8, nursing period around28~35 days, and the survival rate of nest1ings was 87.7%. The reproductive3capacity of one little egret was l .96 per year, and the survived nestlings fOrone nest was 3.37. The mea-n clutch size in pond herons was 3.96l0.42,incubation period 22.3 days, incubation rate 90.9%, mean number of thenestlings was 3.58l0.8l, and the survival rate of nestlings was 89%. Thereproductive caPacity of one pond heron was l .80 per yeap and the survivednestli11gs fOr one nest was 3. l9.'I hLrough the comparisorl of the breedi11g process, their clt1tch size wasdiffercnt significamly, hl)wevef, the number of the nestlings;1nd survivals,the incubation rate and survival rate were not different significantly betweentwo species.Both the little egret and pond heron had a mechanism to adjust theincubation time in the hatching process. The length of incubation period wasnegatively correlated with the laying sequence of egg. The incubation periodof the eggs laid early was longer than those laid lately. This incubationadjustment of parents makes the synchrony in hatching and the hatchingintervals of nestlings shorter than the laying intervals of eggs. Thisphenomenon was perhaPs resulted from the incubating behavior differenceof parents in laying time and incubating time. The research also fOund thatthe groWth rate and survival rate in the latest hatched nestlings in little egretwere lower than the earlier hatched ones. ln pond heron the fifth egg andnestling was much less, then the nestlings grew in more balance. The resultsindicate that incubation adjustmellt is an adaptation to favor hatchingsynchrony, which in turn balances the growth of nestlings and increasestheir survival rate.The growth of nestlings of in little egret and pond heron appeared in Scurve. The nestling of pond heron possessed larger speed than the one oflittle egret in the groWth of the weight, length and the different segments ofbody. In addition, the growi;h speed of body segmellts was related to theappearance of specific behavior in various phage of groWth.The fOod habit of 1itt1e egret and cattle egret were analyzed by getting4the fOod disgorged by nestlings. The two egrets all preyed on small animals.The fOod of cattle egret was mostly spider, locust, cricket and frog. The fishof Mugilidae and Cyprinidae and the shrimp were the most food of littleegret.