| Xisha Islands are located in the Midwest of the South China Sea,Southeast of Hainan Island,are the sacred territory of China.As an important habitat for birds,mammals,and transfer station for migratory birds,Xisha islands have innumerous social and economic value.In this study,birds and small mammals of Xisha Islands were surveyed in 13 islands by using line transects from April 2018 to September 2020,species composition and diversity differences compared with historical records were analyzed.A total of 28,327 individuals of birds,belonging to 13 orders,26 families,77 species,including 37 newly recorded species,eight national second-class protected animals,were recorded in Xisha Islands.A total of 41 species of birds are widespread species.23 are Palaearctic species,and 13 are Oriental species;and 35 species of birds are winter visitors,28 are residents,seven are passage migrants,five are summer visitors,and 3 are vagrant visitors.58 species in Dong island,37 in Yongxing island,18 in Zhongjian island,15 in Jinqing island,13 in Chenhang island and Guangjin island,12 in Shanhu island,11 in Ganquan island,10 in Jinyin island,nine in Lingyang reef,seven in Zhaoshu island,six in Yinyu reef,five in Yagong island,and only one specie in Quanfu island.Bird species richness,diversity,and evenness in the rainy season were higher than those in the dry season.Much attention should be paid to Lincoln Island because it is the only large breeding ground of Sula sula in China.Compared to the data published in 1974 and 2005,species richness of birds,especially the resident bird species has increased,and the structure of bird community has changed greatly.The distribution of bird species in the13 islands is in accordance with the species-area relationship.Animals have little influence on seed dispersal of plants,and the bird-plant network is relatively simple.These results suggest that,the bird species in Xisha Islands are characterized by high richness,a major proportion of migratory birds,great differences between islands,seasons and years,an increasing number of resident species,the only breeding ground for S.sula,being affected by island area and habitat richness,and little dispersal relationship between seeds with animals.As important transfer stations of migratory birds and key habitats of S.sula,Xisha Islands should be paid much attention in conservation.According to a 2-year investigation on Dong Island of the Paracel Islands,South China Sea,we assessed the roles of different habitats at the species level and community level of birds using topological and network analysis.Except for more than one hundred thousand individuals of S.sula inhabited the forest,there were 56 bird species,representing 22 families and 12 orders,inhabiting wetland,forest,shrubland,grassland,and/or beach.The bird-habitat network had high nestedness,and bird species showed obvious clustering distribution.Integrated topological and network analysis showed that wetland had a high contribution to species diversity and network structure,and it was a cluster center of migrant birds.Forest and grassland were species hub and connector respectively,and forest was also the key habitat for residents.Beach and shrubland were peripherals.The loss of wetland and forest will result in a sharp reduction of species richness,and even make the S.sula and most resident birds become extinct.These results suggest that the wetland and forest habitat on the focal island are crucial to migrant birds and resident birds respectively,and therefore much more research attention should be paid to the conservation of key habitats in island ecosystems.Three species of small mammals were recorded,of which,Suncus murinus was common in forests and shrubs,whereas Rattus norvegicus and R.flavipectus were trapped near houses.The result suggests that,in Xisha Islands,small mammals have a low species richness and are mostly related to human activities,the related ecological effects should be investigated and paid attention to. |
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