| Shanghai is rich in bird diversity. As a densely populated international metropolis in eastern China, rapid economic development of Shanghai has added tremendous pressure on its natural environment. Many studies indicate that in the last twenty years, land use change, invasive alien species and other local environment alteration introduced by human activities have lead to dramatic changes of bird habitats status in Shanghai, while global climate change might also bring impact to bird community. Through the integration of field survey, specimen inspection and literature review, this study investigated changes of bird species in Shanghai from 1980s to the first decade of 21st century, discussed the causality of changes in birds numbers and potential impact of climate change. Hooded Crane(Grus monacha)was chose as a case study to explore bird adaptation under environmental changes, and to provide scientific basis for bird conservation policy in Shanghai.The main conclusions of this study are as follows:1. A total of 436 bird species, belonging to 20 orders and 58 families, have been recorded in Shanghai since early 20 century. Since 2000, there have been 370 bird species recorded. Comparing with the bird records in the early 1990s, there are 52 species of new records while 67 species of historical records were absent. Results from analysis into changes of air temperature and birds diversity of Shanghai in the last thirty years showed that the annual mean temperature and winter mean temperature had significantly increased, while in the newly-recorded birds, species number of birds spread from south was significantly larger than those from north, although many new records actually might be missing species in historical investigation. This showed the impact of climate warming on the composition of birds in Shanghai, which made species with southern distribution easier to spread into Shanghai. Therefore climate change and environmental alternation might be one of the reasons for the change of bird species change. Moreover, bird watching increased the opportunity of discovery of new records. Bird watching records of birdwatchers provide important references for understanding the current status and dynamics of bird diversity.2. Logistic regression analyses were employed to investigate the relationship of the population trends of 53 species of waterbirds that showed significant changes with their habitat characteristics, residential status, and ecological guild. The results showed that the best-fit model to explain waterbirds population trends is the model using habitat type and residential status as two independent variables (Anatidae treated as a waterbirds group whose major habitat type including both natural and artificial wetlands), or the single independent variable model only using habitat type (Anatidae treated as a waterbirds group that only depends on natural wetlands). The waterbirds population trends were mainly caused by habitat alterations. Birds strongly depended on natural wetlands showed significant population decline, which might be directly caused by the loss and degradation of natural wetlands in Shanghai in the last 20 years. On the other hand, waterbirds populations using artificial wetlands as major habitats showed increasing trends, which could be probably related to the raising area of artificial wetlands (especially aquaculture ponds). Since different groups of waterbirds have specified habitat use, the Shanghai government should intensify conservation on natural wetlands to maintain waterbird populations3. The corms of sea-bulrush(Scirpusmariqueter) are the main natural food resurces of hooded crane at Chongming Dongtan. Exposed corm density increased slightly during November, but then declined as winter progress. The increased corm density in early winter than late winter demonstrated a declining trend of food resource availability during wintering period. Tidal activity also showed a strong effect on the abundance of exposed sea-bulrush corms, more corms were found during spring tide than any other period between two succeeding spring tide. Hooded crane changed its foraging site and food type during wintering in response to the tremendous declining of its natural food-corms of sea-bulrush from foraging corms at outer sea-bulrush zone during the whole wintering period, to foraging corms at mudflat during early, early-middle and late period of wintering, and foraging rice panicles and wheat seedlings in the cultivated farmland at late-middle stage of wintering. Feeding success within 4 minutes in farmland during mid-winter was significantly higher than those in intertidal flat during any period (early period, mudflat:18.2%±6.3%; middle period, mudflat:21.8%±15.0%; late period, mudflat: 25.9%±14.7%; middle period, farmland:54.1%±12.6%, Kruskal-Wallis Test-χ2= 60.5, df=3,p<0.001), but the disturbance frequency to hooded crane was also much higher in farmland than that in mudflat (farmland:1.41 h"';mudflat:0.27 h-1). Thus the foraging site choosing behavior of hooded crane could be a result from the trade-off of demands between raising feeding efficiency and avoiding disturbance.Grazing on the tidal flat caused declining of area-based corm production in sea-bulrush communities, which reinforced the negative impact of large-area sea-bulrush vanishing caused by the spread of Smooth Cordgrass (Spartina alterniflora)on hooded crane. Actions like grazing reducing at intertidal zone should be established to restore natural habitat for cranes, and sound management measures should also be developed for rice paddies after harvesting to reduce disturbance from human activities... |
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