| Habitat selection exists in multiple forms throughout the life history stages of migratory waterbirds,directly or indirectly affecting the reproductive success rate,spatial distribution pattern,and food resource availability of waterbirds,which in turn lead to changes in habitat preferences and foraging strategies.According to the changes in habitat suitability in different breeding areas,stopover site areas,and wintering areas,waterbirds make adaptive adjustments to habitat selection patterns,distribution patterns,and behavioral responses.Suitable nesting habitat includes suitable nest sites and nest support structures,both of which together affect the reproductive success of the waterbirds.Habitat quality affects wintering strategies of waterbirds and their rapid adaptability to habitat changes determines the complexity of their response mechanisms to dynamic changes.Therefore,exploring the pattern of nest site selection,wintering foraging strategies,and changes in spatio-temporal patterns is important to understanding the mechanism of waterbirds’habitat selection and guiding habitat protection and management.Oriental Stork（Ciconia boyciana）is a large and endangered wader.It is generally believed that its breeding areas were mainly in the Sanjiang Plain and the Russian Far East,and its wintering areas were mainly in the middle and lower Yangtze River.Due to environmental changes over the past few decades,the quality of suitable breeding and wintering habitats has declined sharply,leading the Oriental Stork to continuously explore suitable new habitats.The nest site characteristics and environmental variables of the Oriental Storks were collected through a quadrat survey in this paper,which focuses on the nest site selection patterns and adaptive nesting strategies of the Oriental Storks in different breeding sites.In addition,the habitat and foraging behavior data of the wintering Oriental Storks were obtained by instantaneous scanning and focus sampling to explore the spatial distribution characteristics,tempo-spatial dynamic changes,and foraging behavior of the wintering Oriental Storks at Shengjin Lake.The main results are as follows:1.The intensity of human disturbance,distance from roads,and oil wells were the key limiting factors affecting the nest site selection of the Oriental Storks in three different nest types in the Yellow River Delta National Nature Reserve.Furthermore,food resources,the intensity of human disturbance,and nesting resources had the greatest impact on nest site selection of the Oriental Storks in three breeding areas,meanwhile,the Oriental Storks adopt flexible nesting strategies to adapt to changing habitats in different breeding areas.The breeding Oriental Storks prefer to select sites which far from sightseeing sites（2517.10±214.09 m）,oil wells（3243.39±173.27 m）,highways（321.84±23.54 m）,and lower disturbance levels（2.45±0.07 degrees;χ2=24.32,P<0.001）in the Yellow River Delta National Nature Reserve.In the three different breeding areas,the intensity of human disturbance and food resources explained 31.03%and 11.61%of nest site selection in the North-east Asian nest area,47.30%and 20.18%in the Bohai Bay nest area.In the Middle-lower Yangtze River nest area,food resource（36.86%）was the most important factor affecting nest site selection of the Oriental Storks,followed by the intensity of human disturbance（20.97%）.Therefore,food resources significantly affect the nest height selection of the Oriental Storks in the North-east Asian nest area(βfood resources=-0.067,95%CI=-0.109～-0.002)and the Bohai Bay nest area(βfood resources=-0.103,95%CI=-0.151～-0.054).The intensity of human disturbance influenced nest height selection significantly in the Bohai Bay nest area(βthe intensity of human disturbance=0.905,95%CI=0.346 to 1.575)and the Middle-lower Yangtze River nest area(βthe intensity of human disturbance=2.094,95%CI=1.209 to 3.064).Nest support structure significantly affected nest height selection in the Bohai Bay nest area(Std.Dev the nest support structure=3.174,95%CI=1.245～7.210)and Middle-lower Yangtze River nest area(Std.Dev the nest support structure=17.300,95%CI=4.791～51.724).2.Under the future climate change,the potentially suitable nesting area of the North-east Asian nest area and the Bohai Bay nest area will be reduced,and the suitable nesting area of the Middle-lower Yangtze River nest area will be expanded.Max Ent model results showed that the potential nest habitat exhibited a patchy distribution,mainly found along the Sanjiang Plain,western parts of Jilin,Bohai Bay coast,northeast parts of Shandong,middle parts of Jiangsu,and coastal areas.A few distributions around lakes are situated along the middle and lower Yangtze River and some adjacent areas.Even though we predicted that the overall nesting geographical range of the storks will expand under both emission scenarios,the gain rate of suitable habitat will still decline and the loss rate will increase.The suitable nesting habitat areas also show discrepant variation trends in different regionals,the loss rate of suitable areas in the Middle-lower Yangtze River nest area both decreased under two emission scenarios in the future,while the net gain of suitable habitat areas was relatively stable and showed an increasing trend.3.The habitat utilization pattern and spatial distribution of the wintering Oriental Storks have dynamic changes.As the water level reduced,the spatial distribution of the wintering Oriental Stork gradually shifted from wide and scattered to dense and gathered,and there was a tendency to move from the lakeside to the center of the lake area.During the 2017-2018 winter,accounted for 64.39±12.22%of the Oriental Storks in the shallow water,was the main foraging habitat in the early wintering period,meanwhile,meadows and dry mudflat accounted for 23.49±10.95%and 12.12±9.29%,respectively.In the middle wintering period,22.02±5.07%of Oriental Storks selected to forage in shallow water,significantly increased from the early stage.At the same time,the number of storks in the shallow water decreased and accounted for 54.87±29.71%of the total number of storks.In the late wintering period,the shallow water still had the highest percentages of the total number of storks（69.29±11.11%）.During the 2018-2019 winter,in the early wintering period,Oriental Stork mainly selected shallow water habitat（60.21±8.25%）,followed by meadow habitat（22.23±11.20%）,and dry mudflat habitat（17.56±8.33%）.In the middle wintering period,the utilization rates of shallow water habitat were 55.26±6.55%,dry mudflat habitat was 20.14±5.27%,and wet mudflat habitat was 19.39±3.29%.In the late wintering period,the utilization rates of shallow water habitat were 72.36±10.36%,and wet mudflat habitat was 24.07±9.65%.In addition,the population distribution areas of the wintering Oriental Stork at Shengjin Lake in the 2018 winter were significantly larger than in the 2017 winter,and the spatial distribution was more concentrated.Furthermore,in the high water level period,Oriental Storks were mainly distributed in small flocks,where the upper of the lake and shallow water areas are at the edge of the Shengjin Lake.With the progress of the wintering period,water began to recede,diversity of shallow water and mudflat habitats were gradually exposed,attracting more storks concentrated in the shallow water area and population size gradually increases,meanwhile,showing the trend of moving from the lakeside to the center of the lake area.4.The foraging activity level of the wintering Oriental Storks was mainly affected by the intensity of foraging activity of neighbors.The foraging activity levels（foraging rate,foraging effort,and foraging success rate）of the wintering Oriental Storks were higher in the presence of neighbors than in their absence.Moreover,these levels were more influenced by the number of neighbors foraging than the number of neighbors,and the foraging activity levels increased considerably with the increased number of neighbors foraging.The wintering storks adjusted their foraging activity levels according to social information gathered from conspecific individual neighbors.The average foraging rate of neighbors positively affected the foraging rate and foraging effort of the focal individual（P=0.041,coeff.±SE=0.009±0.004;P<0.001,coeff.±SE=0.063±0.004）,while the foraging success rate of focal individuals was significantly enhanced when the neighbors increased their average foraging effort（P<0.001,coeff.±SE=2.187±0.107）.In conclusion,there were significant differences in the nest habitat characteristics and nest site selection patterns of the Oriental Stork in different breeding places,and storks had flexible nesting strategies to adapt to the habitat changes of different breeding areas under the background of breeding places expansion.The changes in the allocation of food resources of the wintering Oriental Stork led to adaptive changes in the spatial distribution,habitat use pattern,and foraging behavior.This study provides a theoretical basis for population protection and habitat management of the Oriental Stork.A systematic and complete investigation was conducted on the breeding sites-stopover sites-wintering sites of the Oriental Stork in this study.To explore ecological issues from the migration connectivity,comprehensively and systematically expound on the habitat use patterns and behavioral adaptation mechanisms of the Oriental Stork during the entire life history stage.Then,providing an important theoretical basis for the protection and management of endangered species. |
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