| Fitness for waterbird species is largely dependent upon the ability to access to high quality food items in heterogeneous environments, particularly on the wintering grounds, where individuals must recover from and prepare for migratory flights. In regions that are experiencing severe human-caused habitat degradation, flexibility in foraging strategies may temper the negative impacts of habitat loss. Understanding the adaptive capacity of waterbirds to efficiently shift their foraging behaviors in response to habitat quality decline over spatio-temporal scales can help to direct future conservation planning for several species. Hooded cranes Grus monacha are large migratory waders that winter in the lakes of the Yangtze River floodplain, which have been severely degraded due to intensified aquaculture. Based on the theories of the Ideal free distribution and the Optimal foraging theory, mirroring the influences of the quantity and quality of foraging habitat resources, particular the food resources. The Hooded cranes should adopt the flexible foraging behavior strategies in response to the degradation and loss of their foraging habitats. It is the goal to make the full use of the food resources in each foraging habitat patches across the harsh winter seasons.Form the October2012to April2013, We investigated the changes in food characteristics and the relative abundance and density of the Hooded cranes in each habitat across winter seasons, examined the influence of winter periods and habitat types on the crane habitat use patterns, and explored the relationship between the habitat use patterns and food characteristics using linear regression. We conducted behavioral observations, measured seasonal and habitat-specific differences in foraging time budget, foraging rate, and capture efficiency, and modeled these metrics as a function of the food abundance, food depth, and sediment permeability.During the winter seasons, Hooded cranes spent their majority of time for foraging, and our results suggested that they shifted their habitat preferences based upon abundance and accessibility of food in different habitats. However, our analyses also indicated that cranes forage at a low capture efficiency (10-15%) with the similar frequency as they do a high capture efficiency (75-80%), suggesting that cranes are willing to forage sub-optimally to satisfy specific nutrient requirements. The food characteristics and the habitat use changed obviously over spatio-temporal scales, and the largest food abundance and accessibility occurred in paddy fields in early and mid-winter seasons, and the largest food abundance in meadows in late winter season, along with the seasonal changes, the main foraging habitat types from paddy fields to meadows. There were few influences of winter periods, habitat types and their interaction. The habitat use was determined by the food abundance, but not dependent on the food depth and sediment permeability.In response to the degradation and loss of the wetlands and the spatio-temporal difference of the food characteristics, the Hooded cranes have befittingly changed their foraging habitat patterns, and adopted the flexible foraging behavior strategies that can facilitate their overwintering survival in degraded wetland mosaic landscapes. Based on our findings, it highlighted the significance of the food abundance and accessibility in the foraging ecology and the life cycle of Hooded cranes. In our opinion, We concluded that the Hooded cranes have mitigated the negative impacts of habitat loss by making tradeoffs between the food abundance and food accessibility including the food depth and foraging sediment permeability, it is would facilitate their survival in degraded wetland mosaic landscapes across the harsh winter seasons, and maintain a relatively stable population of Hooded cranes in the wintering ground along with the middle and lower Yangtze River floodplain. |
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