The Breeding Ecology And Population Dynamics Of The Little Egret (Egretta Garzetta) In Dayu Islet, Xiamen Egret Natural Reserve

The breeding ecology and population dynamics of the little egret (Egretta garzetta) in Dayu Islet, Xiamen Egret Natural ReserveWuLie(School of Life Sciences, Ximen University, Xiamen 361005)(Abstract)Xiamen Egret Natural Reserve includes two parts: Jiyu Islet and Dayu Islet. The breeding ecology and population dynamics of the little egret (Egretta garzetta) were studied in Dayu Islet from March 1999 to July 2001.The little egret used the marshland next to the west of Dayu Islet as a "lek" in non-breeding season, and used Dayu Islet as the nesting, reproducing and feeding site in breeding season.Population size of breeding Ardeidae in Dayu Islet in 1999 was 4112 pairs in total and their nesting area was 1. 14X 106 in2, in which there were 1848 pairs of !Vycticorax nyc ticorax, 1304 pairs of Egretta garzetta, 896 pairs of Ardeola bacchus, 56 pairs of Bubulcus ibis, and 8 pairs of Egretta eu]ophotes. In 2000, the total population number of the breeding Ardeidae in Dayu Islet was 572 pairs and nesting area was 3. OOX 104m2, in which the Egretta garzetta was 474 pairs, and Ardeo]a bacchus 98 pairs. In 2001, total population number was 828 pairs and nesting area 3. 25 X 104m2, and the population number of Egretta garzetta, Nyc ticerax nycticorax, Ardeo]a bacchus, and Bubu]cus ibis was 638, 112, 78, and 20 respectively.There was a spatial distribution when ardeids breeding in Dayu Islet. Firstly, the colonial breeding ardeids showed a horizontal distribution. Nyc ticerax nyctzcorax mainly distributed on southern region in the center of the core area. Egretta garzetta bred in all regions of the core area. Ardeolabacchus only nested on both northern and southern sides of the core area. Bubu]cus ibis and Egretta eulophotes set their nests on the North of the core area, sharing the place with Egretta garzetta and Ardeola bacchus. The colonial breeding ardeids also showed the vertical distribution. Nyc ticerax nycticorax located their nests on the tiptop of the forest, and Egretta garzetta, Bubulcus ibis and Egretta eu]ophotes set their nests in the middle. When Egretta garzetta and Ardeola bacchus nested on the same tree, the latter usually nested in the higher location.Egretta garzetta settled into the nesting sites on Dayu Islet around Tomb-sweeping Day after frequently examining the nesting sites. Soon they made the courtship, partnership, and copulation and set their nest. Their nests appeared as basin-shape. All nests were built with branch of deadwood, which was taken from ground, trees or from old nests. The height between nest and ground is 4.53±1.38 m. Inner radii of the nest was 28.38±7.06 cm, outer radii 38. 12±6.59 cm, depth 4.26± 1.34 cm, highness 15. 61±2. 43 cm. The clutch size of the little egret was 3.79±0. 71, egg weight 24.02±2. 15 g, egg length 44.5 ±0.22 mm, egg width 32. 1±0. 11 mm0 The parents hatched their egg by turns, and the incubation period is 24-25 days. During incubation, the parents turned eggs over and stand up or leaf the nest for regulating the temperature of the egg. Hatching rate was95.5% in 1999~, 85.6% in2000, and90.9%in200l. Hatchling of Egretta garzetta was altricial, and raised by both parents. The length of nursing period was 30. 07±2. 52 days. The survival rate in nursing period was 73. 5% in 1999, 65. 1% in 2000, and 85. 1%in 2001~ The body weight, body length and wing length of the nestling grew fast before 22 days, but then gradually became slower.With the change of nestling's age, the parents changed theirfeeding time, feeding distance and feeding way for feeding their nestlings. The dietary analysis showed that the nestlings of Egretta garzetta fed on fish and shrimps. Their main feeding places were seashore, estuary and shrimp pounds. Different age of little egret fed on prey in different length, breadth and quantity. Little egret at one week age only fed small size and a little of prey. With the egret getting older, the mean length, breadth and quantity of its prey increase, which was positive...