| In order to explore the influence of the Three Gorges Project on the wetland birds in the reservoir area, including the changes on diversity, distribution pattern and population quantity, and to provide comparative data of ecological environment after the completion of the Three Gorges Dam, from 2003 to 2013 (except 2011), we carried out a monitoring survey upon the birds′ distribution status during the middle of winter along the main river of the Changjiang River and the 12 primary tributaries, and in 2 lakes (from 2000 to 2013, except 2003 and 2011) of the Three Gorges Reservoir area.
The Changjiang River in the Three Gorges Reservoir area is divided into different segments and the lengths are as follows: Chongqing (Chaotianmen Wharf)﹣Changshou (74.20 km), Changshou﹣Fuling (47.80 km), Fuling﹣Fengdu (52.80 km), Fengdu﹣Zhongxian (63.90 km), Zhongxian﹣Wanzhou (89.40 km), Wanzhou﹣Yunyang (old town pier) (63.10 km), Yunyang﹣Fengjie (64.00 km), Fengjie﹣Wushan (40.40 km), Wushan﹣Badong (56.50 km), Badong﹣Zigui (Mao Ping Wharf) (66.20 km), the whole journey is about 618.30 km. We also investigated 12 primary tributaries, their names and the length from the mouth to the upper reachesare as follows: Jialingjiang (56.90 km), Mudonghe (11.60 km), Wujiang (236.25 km), Xiaojiang (69.00 km), Tangxihe (30.00 km), Modaoxi (22.80 km), Meixihe (18.00 km), Daxihe (14.10 km), Daninghe (68.00 km), Yanduhe (25.50 km), Xiangxihe (31.79 km), Jiuwanxi (12.82 km). The total length of these tributary rivers is about 619.49 km. Two artificial lakes were also investigated, one is the Changshouhu Lake of 65.5 km2, about 22 km from the Changjiang River, built in 1956; the other is the Dahonghu Lake of close to 30 km2, about 17 km from the Changjiang River, built in 1958.
The annual bird surveys were conducted during 8th to 28th in January. Observers made censuses of the birds at the front deck of a passenger ship by using hand-held binoculars, with unilateral width of 300 m (bilateral width 600 m), and recorded bird species and numbers, also the sample line survey data and information. The ship′s speed range was from 10 to 24 km/hour. After the water level reached 156 m, as daytime long-distance passenger ships were gradually reduced or even disappeared, we took small fishing boats (speed range from 8 to 12 km/h) for the census. For some branch rivers we could not sail (normally before the water level reached 175 m), we made line transects for bird censuses on foot or by low-speed car (10﹣20 km/h).
A total of 76 bird species belonging to 8 orders and 14 families were recorded, with one species (Scaly-sided Merganser Mergus squamantus) listed as the Level Ⅰ National Key Protected Wild Animals and 3 species (Horned Grebe Podiceps auritus, Red-necked Grebe P. grisegena and Mandarin Duck Aix galericulata) being the Level Ⅱ. The observed birds were divided into 5 communities: the natatory birds (32 species), the gulls (6 species), the waders (23 species), the river-closing birds (13 species) and the birds inhabiting above the water (2 species, mainly the Sand Martin Riparia riparia).
The results indicated that these bird communities were different greatly in reaction to the variation of water environment before and after the water level rising to 139 m, 156 m and 175 m of elevation. Quantity fluctuation of the natatory birds were not obvious before and after the water level rising to 139 m, however, when the water level reached to 156 m (Jan. 2007), their number showed an increasing trend until the final 175 m water level during the fifth winter (Jan. 2013), and soared to the highest value of 3 860 individuals, 2.72 and 2.80 times as many as in the January of 2003 and 2004, when the water level was lower and over 139 m (Appendix 1). The natatory birds in the 2 lakes showed downward trend, with the number of birds fell by 83.29% (in 2009) to 52.96% (in 2013) after the water level of 175 m (2008﹣2013, except 2011) compared with that in 2000 (Appendix 6). In most of the tributaries of the Changjiang River, the number of natatory birds showed small fluctuations or obviously decreasing, only in Wujiang River and Xiaojiang River showed a growth trend. The number of natatory birds in the Xiaojiang River was showing explosive growth phenomenon and then fell sharply (2012﹣2013), the relevant change might be related to the degree of eutrophication. The gulls were mainly distributed in the main channel of the Changjiang River, and their peak values appeared in the early stages of different water storage period (Appendix 2), possibly related to the amplification of the initial impoundment of water, as floating objects on water may be a potential source of food. The wader′s distribution pattern was similar to the natatores, with the number reaching the peaks in the first winter after the 139 m and 156 m water levels, however, without much quantity difference in other years. There were not much waders in most tributaries of the river, only in the Jialingjiang River, Wujiang River, Xiaojiang River, Daninghe River and Meixihe River, there were large number of waders and showed obvious numerical fluctuations between years (Appendix 3). The total number of the river-closing birds and the birds inhabiting above the water (mainly Sand Martin), showed a sharp change in the water level before and after the rise, their numbers dropped significantly, and some species even disappeared (Appendix 4, Appendix 5).
In summary, water storage showed positive or negative effects on different communities of birds in the Three Gorges Reservoir Area. It might be positive effects for the swimming and wading birds, for example, water surface expansion (main river channel of the Changjiang River) and water eutrophication (Xiaojiang River), but excessive eutrophication will be a negative impact such as the Daninghe River and other tributaries. It had negative effects for the river-closing birds and birds inhabiting above the water (mainly Sand Martin), as their nesting habitat were flooded and the loss of their food source. |
