The Functional Response And Behavioral Adaptation To The Changes Of Food Resources For Wintering Bewick’s Swans(Cygnus Columbianus)

The wintering process of migratory waterbirds has decisive effect on the annual life cycle,and foraging strategies is a presentation of functional response and behavioral adaptation to the changes of food resources for waterbirds,which is an important field of waterbirds’ecology.The foraging behaviors of wintering waterbirds are influenced by many habitat factors,which need waterbirds to adapt the change of habitat conditions by optimizing behavior strategy,and it is positive significance to improve individual fitness for wintering waterbirds.Therefore,the work that focus on waterbird’s behavioral strategies,such as response to disturbance,foraging functional response,giving-up net energy intake rate were took more attention for management and conservationists,in particular,the behavioral strategies of wintering waterbirds under human disturbance is hot spot of avian behavioral ecology.The shallow lakes in the middle and lower Yangtze River floodplain,especially the Shengjin and Huangpi lakes,are important resting and wintering grounds for waterbirds on the East Asian-Australasian Flyway.The flora and fauna in wetland habitats provide food supply and security for wintering waterbirds.The availability of food resources for wintering waterbirds is affected by seasonally environmental factors such as food density,water depth,sediment compaction,and human disturbance,which causes the waterbirds develop different behavioral strategies to satisfy energy needs.In recent years,the wetland ecosystem of Shengjin and Huangpi lakes had been degraded due to the lake reclaim and purse seine fishery,moreover,anthropogenic disturbance aggravated the degradation of wintering waterbirds habitats.As a result,the microhabitat factors such as food resources,water depth,sediment compaction present unnatural changes.Therefore,the foraging activities of wintering waterbirds in these lakes,such as Bewick’s Swan（Cygnus columbianus）,are inevitably affected,and reflected in change and adaptation of the wintering behavior strategies.This study focus on the swans wintering in Shengjin and Huangpi lakes,meanwhile,study the behaviors and time budget characteristics of wintering Bewick’s Swans in different wintering periods and habitats through surveying the microhabitat factors by quadrat method,and foraging behaviors by instantaneous scanning and focal animal sampling.Integrating the microhabitat factors,the effects of seasonal dynamics,habitat types,food density,water depth,sediment compaction and disturbance on the time budget,functional response of feeding rate,and giving-up net energy intake rate of foraging swans were studied,then the behavior patterns and ecological adaptation strategies for wintering swans were elucidated.The results as follow.1.Anthropogenic disturbances reduced the foraging activity of wintering swans and increased energy expenditure rates,and the swans increased total vigilance behavior to adapt anthropogenic disturbances.The total vigilance time percentage of wintering swans in disturbed habitats（8.145±1.201%）were larger than normal habitat,while foraging behaviors were lower（75.263±18.445%）.The swans’time budgets of foraging behavior were positively correlated with disturbance distance and food density(r _{food density}=0.109,r _{disturbance distance}=0.189,overall P<0.05),while it is negatively correlated with the percentage of disturbance time（r=-0.290,P<0.05）.The total vigilance time percent decreased with the food density（r=-0.118,P<0.05）,suggesting that swans in higher food density patches increased foraging time and decreased alertness.There is a linear relationship between the disturbance time percentage and overall vigilance time percentage,moreover,the energy expenditure rate was positively correlated with the disturbance time percentage and disturbance distance.2.Bewick’s Swans adopted flexible functional response in heterogeneous foraging habitats.The observed feeding rate and the percentage of disturbance time decreased with the winter processed.Searching rate（0.077705±0.011485 m²/s）,handling time（1.309±0.055s/item）and percentage of total vigilance time（8.653±0.870%）in middle winter were larger than other winter periods.Observed feeding rate,searching rate and handling time varied in different habitats,observed feeding rate in lake（0.019±0.001 items/s）was larger than foxnut ponds and paddy fields,however,searching rate（0.106870±0.015899 m²/s）and food density（793.291±34.578 items/m²）in paddy fieldswere the highest,meanwhile,handling time（1.298±0.047 s/item）and disturbance time percentage（20.764±2.332%）in foxnut ponds were the highest.There were complex relationships between the components of the functional response.Observed feeding rate was not correlated with food density（r=0.323,P>0.05）and displayed a negative relationships with handling time（r=-0.428,P<0.05）.Handling time was negatively correlated with food density and flock size(r _{food density}=-0.244;r _{flock size}=-0.195,overall P<0.05).Searching rate was positively correlated with food density（r=0.141,P<0.05）.3.The swans demonstrated diverse patterns of giving-up net energy intake rate in different foraging habitats under variation of heterogeneous microhabitat factors,such as natural and anthropogenic factors.The giving-up net energy intake rate decreased in lake（132.428±8.747 J/s）,foxnut ponds（77.858±7.148 J/s）and paddy fields（11.343±2.486 J/s）,and were significantly different among the three habitats.The giving-up food density（29.245±1.323 g/m²）,water depth（51.269±3.870 cm）,sediment compaction（146.461±4.678N/cm²）in foxnut ponds were higher than other habitats,however,wintering days was conversely（55.852±3.294 d）.The habitat type,water depth,giving-up food density,sediment compaction,and percentage of disturbance time had significantly effect on giving-up net energy intake rate.The swans would decrease their giving-up net energy intake rate under unfavorable foraging conditions such as more disturbance（r=-0.382,P<0.05）,however,giving-up net energy intake rate would increase with water depth and sediment compaction（r shallow water=0.561,r deep water=0.437,r sediment compaction=0.449,overall P<0.05）.Giving-up net energy intake rate decreased with giving-up food density in deep water as winter progressed（r=-0.578,P<0.05）.The giving-up net energy intake rate could be used to evaluate the effects of different microhabitat variables on habitat switching of wintering swans.In summary,swans foraging in habitats adapt to the changes of natural factors and human disturbance in degraded wetlands by adjusting the behavior time allocation,functional response and giving-up net energy intake rate in different wintering periods.These foraging and switching patch strategy provide important information for the management and conservation for waterbird populations and their habitats.