Lower Yangtze River Floodplain Research Articles

Effects of constant high water levels in winter on waterbird diversity in Caizi Lakes: A functional perspective

The middle and lower Yangtze River floodplain lakes are important stopover and wintering sites for migratory birds on the East Asian–Australasian Flyway. The periodic water level fluctuation of the lakes plays a critical role in the aggregation of waterbirds. However, the construction of a series of gates and dams has impeded the hydrological connectivity between rivers and lakes and disrupted the natural water level fluctuation patterns of lakes. The water level status of lakes influences habitat utilization by waterbirds. In recent years, Caizi Lakes, the gate-controlled lakes connected to the Yangtze River due to the need for water level regulation requirements, has experienced sustained high water levels in winter, which can reduce habitat quality and in turn influence waterbirds activity. In the present study, wintering waterbirds in Caizi Lakes were surveyed during the 2021–2022 (W1) and 2022–2023 (W2) wintering periods. Moreover, we explored the effects of constant high water levels in winter on waterbird assemblages by comparing species richness, abundance, and functional alpha and beta diversity. Correlation analyses were then performed to elucidate the relationship between habitat factors and water level changes during the wintering period of migratory waterbirds and between changes in various habitat factors and wintering waterbird assemblages under different hydrological conditions. The results showed that functional beta diversity was more sensitive to changes in waterbird assemblages in Caizi Lakes than functional alpha diversity. Moreover, constant high water levels in the mid-wintering period decreased suitable habitats for wintering waterbirds, increased functional turnover among waterbird assemblages, increased total dissimilarity among assemblages significantly, and decreased the level of functional nestedness significantly. Additionally, the areas of the three wetland habitats in Caizi Lakes were significantly correlated with water level changes during W1 and relatively less affected by water level changes under constant high water level conditions during W2. The changes in habitat area were influenced primarily by anthropogenic activities, with an increase in meadow area favorable for species richness and abundance, as well as functionally nested components. Water level regulation should take into consideration the natural hydrological rhythms of the declining water level to ensure that adequate and suitable habitats are provided for wintering waterbirds.

Effects of Habitat Change on the Wintering Waterbird Community in China’s Largest Freshwater Lake

Poyang Lake wetland in the middle and lower Yangtze River floodplain provides important wintering sites for migratory waterbirds. Extreme climatic events and human activities have resulted in the degradation and redistribution of habitat over the last few decades. However, the effects of habitat changes on the abundance of waterbirds remain unclear. We used long-term waterbird monitoring data and Landsat remote-sensing data to characterize changes in abundance and the relationship between habitat variation and abundance. A total of 113 waterbird species were recorded in the wintering period between 1999 and 2021, including 23 globally threatened species. Greater White-fronted Goose (Anser albifrons), Swan Goose (Anser cygnoides), Bean Goose (Anser fabalis), and Tundra Swan (Cygnus columbianus) were the dominant species. A total of 46 species with more than 6 annual surveys and average abundance >100 were recorded between 1999 and 2021. For most species, the mean abundance across all sub-lakes was higher in the first year than in the last year, and no obvious changes were observed over the last 20 years. The mean abundances of the vulnerable species Hooded Crane (Grus monacha) and White-naped Crane (Grus vipio) significantly declined between 1999 and 2021. No significant changes in the mean abundance of all foraging groups were observed. The area of water bodies increased, and the area of mudflats decreased. For most species with significant changes in abundance, habitat change did not greatly contribute to variation in mean abundance. The reduction in the area of mudflats greatly contributed to declines in the mean abundance of the gray heron (Ardea cinerea) and gadwall (Anas strepera).

Intestinal Microbiota of Anser fabalis Wintering in Two Lakes in the Middle and Lower Yangtze River Floodplain.

The intestinal microbiota of migratory birds participate in the life activities of the host and are affected by external environmental factors. The difference in habitat environment provides diversity in external environmental selection pressure for the same overwintering waterfowl, which may be reflected in their intestinal microbiota. Caizi lake and Shengjin Lake in the Middle and Lower Yangtze River Floodplain are the main habitats for migratory waterfowl in winter, especially the Anser fabalis (A. fabalis). It is important to explore the changes in intestinal microbiota composition and function of A. fabalis in the early overwintering period to clarify the effect of habitat size and protection status on intestinal microbiota. In this study, the composition and structural characteristics of the intestinal microbiota of A. fabalis in Shengjin Lake (SL) and Caizi Lake (CL) were preliminarily explored in order to obtain data for the migratory birds. In both SL and CL groups, 16S rRNA amplicon sequencing analysis showed that Firmicutes was the dominant bacterial phylum, but the relative abundance showed significant differences. Lactobacillus was the most abundant genus in both SL and CL groups. At the species level, the abundance of L. aviaries was the highest, with a relative abundance in both SL and CL groups of more than 34%. When comparing the average relative abundance of the 15 most abundant genera, it was found that Subdoligranulum, Exiguobacterium, and Terrisporobacter had higher abundances in the intestinal microbiota of CL A. fabalis, while Streptococcus and Rothia had higher abundances in the intestinal microbiota of SL A. fabalis. There was only a positive correlation between Bacteroidota and Proteobacteria in the intestinal microbiota flora of SL A. fabalis, and the species were closely related. At the same time, there were positive and negative correlations between Firmicutes and Actinomycetes. However, CL is mainly associated with a positive correlation between Firmicutes and Actinomycetes, and there are also a small number of connections between Firmicutes. PICRUSt1 prediction analysis revealed that the Clusters of Orthologous Groups (COG) functions of SL and CL involve energy production and transformation, amino acid transport and metabolism, carbohydrate transport and metabolism, and transcription. Understanding the changes in intestinal microbiota in Aves during the overwintering period is of great importance to explore the adaptation mechanism of migratory Aves to the overwintering environment. This work provides basic data for an A. fabalis intestinal microbiota study.

The impact of earlier flood recession on metacommunity diversity of wintering waterbirds at shallow lakes in the middle and lower Yangtze River floodplain

The hydrological regime in wetlands plays an important role in the process of wintering waterbird metacommunity assemblage. However, increasing frequency of extreme climate and the intensification of human activities, such as the construction of sluices and dams, have resulted in frequently abnormal hydrological regime in the middle and lower Yangtze River floodplain. In recent years, earlier flood recession has become one of the main hydrological problems faced in the shallow lakes, having a great impact on wetland biodiversity. It is necessary to understand the impact of earlier flood recession on waterbirds, an indicator of wetland biodiversity, and the metacommunity concept is helpful to elucidate the underlying mechanism involved in the processes of assemblage by waterbird communities. In this study, we surveyed the wintering waterbirds at three sub-lakes of Caizi Lakes during 2019–2020 and 2020–2021 and compared the richness, abundance, alpha and beta diversity of waterbirds in and among local metacommunities under earlier flood recession and normal hydrological regime . The results showed that the earlier flood recession reduced the species richness in the early stage and abundance in the late stage, it also reduced the Shannon–Wiener index in the early stage and increased the dissimilarity between and within waterbird metacommunities in the late stage. The partition of beta diversity showed that the turnover component played a major role in the process of waterbird metacommunity assemblage. It was found that the earlier flood recession reduced the richness, abundance in different stages of flood recession, which also increased the turnover of waterbirds. Metacommunities with high habitat heterogeneity had better resistance to abnormal hydrological regime, which resulted in high dissimilarity between and within metacommunities. The results of this study provide important information for waterbird conservation and water level management at shallow lakes in the middle and lower Yangtze River floodplain.

Flexible nest site selection of the endangered Oriental Storks (Ciconia boyciana): Trade-off from adaptive strategies

Nest site selection is a vital component of bird reproduction success, and an adaptive behavior conducted to decrease nest predation risk with avoiding external disturbances. Understanding patterns of nest site selection can provide insights into how species adapt to changes in their habitat and has important conservation implications. In this study, we used microhabitat variables and multi-scale data with a field survey of nest occurrence to determine nest site selection patterns and adaptive strategies of the breeding Oriental Storks (Ciconia boyciana) in different nest areas. Results demonstrate that the nest site microhabitat characteristics of the breeding Oriental Storks significantly differed among the three nesting areas, and nest height was higher in the middle and lower Yangtze River floodplain than in the Northeast China and Bohai Bay nest areas. The food resources and intensity of human disturbance had the greatest effects on the nest site selection of the breeding Oriental Storks. The intensity of human disturbance was positively correlated with the nest height of the breeding Oriental Storks in Bohai Bay and the middle and lower Yangtze River floodplain; however, nest height decreased with the abundance of food resources in the Northeast China nest area. Our findings indicate that the nest site selection patterns of Oriental Storks showed flexible adaptive strategies. In safer environments, nests were lower and closer to food resources, which allows parent storks to invest more in the nestlings. However, in areas where human activity was intense, nests were higher to ensure the safety of their offspring. Some measures that could be taken to improve the breeding habitat of Oriental Storks include increasing the percentage of wetland areas in nesting areas to enhance food resources availability and setting artificial nests at suitable heights in potential nesting grounds to encourage nesting. Finally, the establishment of soft barriers around the nesting areas could increase the safety of nests.

Wintering waterbirds diversity and their impact factors in coastal lake wetlands of the Yangtze River in Jiangsu Province

长江及其中下游湖泊湿地组成了独特的江-河复合型生态系统，孕育了极高的生物多样性，是全球生物多样性研究的热点区域之一.该区域是东亚-澳大利西亚迁徙通道上最重要的水鸟越冬地之一，每年冬季有超过百万只水鸟在此越冬，因此，分析相关因素对越冬水鸟多样性的影响对维持其越冬安全具有重要意义.然而，目前相关研究多集中在如鄱阳湖、洞庭湖、升金湖等部分国家级保护区内，对经济较发达的江苏省沿江区域湖泊湿地水鸟多样性的研究仍不多见.本研究选择江苏长江沿江10处代表性湖泊湿地，于2018—2020年冬开展越冬水鸟调查，同时结合环境和人为因素，分析其对区域越冬水鸟多样性的影响.3次调查共记录到越冬水鸟42种109998只，隶属于6目9科.按地理区系划分，古北界16种，广布种15种，古北界-东洋界9种，东洋界2种；按生态类群划分，有游禽22种，涉禽20种.在10处湖泊湿地中，石臼湖水鸟物种数和数量均最多，金牛湖水鸟物种数和数量均为最低；Shannon-Wiener和Inverse-Simpson多样性指数最高的为石臼湖，最低分别为长荡湖和昆承湖.β多样性结果表明石臼湖水鸟群落与其它湿地相似性最低，长荡湖次之.β多样性分解分析结果显示，区域β多样性主要形成机制为物种替换.石臼湖对区域β多样性的相对贡献显著高于其它湖泊湿地，其次是长荡湖，相对贡献最低的是尚湖.线性模型结果表明：越冬水鸟丰富度与湿地总面积呈正相关，与缓冲区植被和水体面积呈负相关.人均GDP与越冬水鸟丰富度呈显著负相关.越冬水鸟物种数与湖泊湿地面积呈正相关，与人均GDP呈负相关.水鸟多样性指数受面积和人均GDP影响均不显著.江苏沿江地区是我国经济最发达的区域之一，对其越冬水鸟多样性及其影响因素开展研究进而提出相关保护建议，如持续开展越冬水鸟监测，及时发现保护空缺，提高对湿地周边区域土地利用状况的关注度等.本研究结果不仅为本地区越冬水鸟保护工作提供依据，同时也为上游经济相对薄弱但发展较快的地区开展相关保护工作提供参照.;The Yangtze River and its floodplain are unique for the extensive wetlands, recharged by summer monsoonal precipitation, laden with nutrients and sediment. It's the largest amount of shallow and seasonal flooded wetlands in the world, providing ecosystem services to tens of millions of people. The wetlands also support globally significant numbers of wintering waterbirds. Every year, more than 1 million waterbirds spend winter here. It is critical to understand the effects of different variables on wintering waterbirds diversity. So far, most of the research were focused on some National Nature Reserves, e.g. Lake Poyang, Lake Dongting and Lake Shengjin. The researches concerning wintering waterbirds diversity on lake wetlands located in the Lower Yangtze River floodplain in Jiangsu Province are still limited, where the economic is relatively developed. In this study, we systematically surveyed 10 representative wetlands along the Yangtze River in Jiangsu Province from 2018 to 2020 and then analyzed the effect of ecological and anthropogenic factors on waterbird abundance, species richness and diversities. In total, 109998 waterbird of 42 species were recorded, belonging to 6 orders and 9 families. Of them, 22 species are Natatores and the others are all Waders. In terms of the biogeographic distribution, 16 species belong to Paleartics, 15 species are wide distributive species, 9 species belong to Paleartics-Oriental, and 2 species belong to Oriental. Among the 10 lake wetlands, Lake Shijiu has the highest Shannon-Wiener and Inverse-Simpson diversity index, and the lowest are Lake Changdang and Lake Kuncheng respectively. In addition, the community composition dissimilarity (β diversity) between Lake Shijiu and the other lakes are the highest, following by Lake Changdang. Results of the decomposition of β diversity suggested that species replacement was the main process influencing regional β diversity. Lake Shijiu had a significant higher relative contribution to regional β diversity, followed by Lake Changdang, while Lake Shanghu had the lowest relative contribution. Wintering waterbird abundance positively correlated with total area of wetlands but negatively affected by vegetation area and water area in the buffer area, as well as the effect of per capita GDP. Number of wintering bird species positively correlated with total area of lake wetlands but negatively affected by per capita GDP. Area had no effects on both Shannon-Wiener and Inverse-Simpson indices. As one of the most developed areas in China, unveiling the effects of different variables on wintering waterbirds diversity may not only offer practical conservation measures for this area, for example, carrying out continuous waterbird monitoring projects, detecting conservation gaps and playing close attention on landscape changes of surrounding area, but also provide a good sample for the conservation work in up-stream areas of the Yangtze River where the economic is ongoing developing.

Intestinal Microbes of Hooded Cranes (Grus monacha) Wintering in Three Lakes of the Middle and Lower Yangtze River Floodplain.

Simple SummaryIntestinal microbes are critical to host health, and are affected by environmental factors. In this study, we investigated the intestinal microbes of Hooded Cranes wintering at three lakes with different environmental characteristics in the middle and lower Yangtze River floodplain in China, aiming to provide insights into the effects of habitat size and protection status of birds on their intestinal microbes. We found that the Hooded Cranes at the smaller lake had higher intestinal bacterial and fungal diversity than those at the larger lake. In addition, more diverse and abundant pathogens were found in the gut of Hooded Cranes that lived in the relatively poorly protected habitat than those that lived in well-protected habitat. This study contributes a new perspective for understanding the intestinal microbes of wintering migratory waterbirds at different habitats, and will help to understand the survival status of the vulnerable waterbirds at different habitats for their better conservation.Intestinal microbes participate in life activities of the host, and are affected by external environmental factors. Different habitat sizes and protection status provide different external environmental selection pressures for the same wintering waterbirds, which may be reflected in their intestinal microbes. Hooded Cranes are vulnerable migratory waterbirds with similar numbers wintering at three different lakes in the middle and lower Yangtze River floodplain, Poyang, Caizi, and Shengjin Lakes. Here, we analyzed the characteristics of intestinal bacterial and fungal communities of Hooded Cranes wintering at the three lakes to clarify the effect of habitat size and protection status on intestinal microbes, using high-throughput sequencing technology. Our results showed that community composition and diversity of intestinal microbes were significantly different among lakes with different habitat size and protection status. The Hooded Cranes at Shengjin Lake (small) had higher intestinal microbial alpha-diversity (for both bacteria and fungi) than those at Poyang Lake (large), which might be induced by social behavior of more waterbirds per unit area. The Hooded Cranes at Caizi Lake (relatively poorly protected habitat) had more diverse and abundant intestinal potential pathogens than Shengjin Lake (well-protected habitat). Our results indicated that the environmental pressure of a habitat might affect intestinal microorganisms and more attention might be needed for the vulnerable waterbirds at the habitat of poor protection status.

Effects of Food Changes on Intestinal Bacterial Diversity of Wintering Hooded Cranes (Grus monacha).

Simple SummaryThe intestinal microbiota plays a vital role in the health of animals, and food is an important factor that influences the intestinal microbial community. During the winter months, waterbirds require certain foods to supply them with energy through the cold winter. Due to changes in the plant resources available to waterbirds, their intestinal bacteria will vary accordingly. In this study, we analysed the relationship between food composition and intestinal bacteria in hooded cranes (Grus monacha). We found that food resources from similar habitats were more similar, and the corresponding hooded crane intestinal bacteria were also more similar. The results show that the intestinal bacteria of hooded cranes had a certain adaptability to the type of food being consumed. This study contributes novel insights into the diet of hooded cranes in the winter months, allowing for improved protection and management strategies.As food is recognised as an important factor affecting the intestinal microbiota, seasonal changes in diet can influence the community composition. The hooded crane (Grus monacha) is an endangered migratory waterbird species, with some of the population wintering in the sallow lakes in the middle and lower Yangtze River floodplain. Their food resources have changed seasonally, with a reduction resulting from wetland degradation. To cope with seasonal changes in food availability, hooded cranes must constantly adjust their foraging strategies to survive. We studied the effect of changes in diet on the intestinal bacterial diversity of hooded cranes at Shengjin Lake, using faecal microanalysis and high-throughput sequencing. The results show that the main foods of hooded cranes were Polygonum criopolitanum, Oryza sativa, and Carex spp., which were significantly related to the composition of the intestinal bacterial community. In addition, foods available from the similar habitats were more similar, and the corresponding hooded crane intestinal bacteria were also more similar. The relative abundance of Lactobacillus acidipiscis in January and March was significantly higher than in November. Our research shows that the intestinal bacteria of hooded cranes actively adapt to diet changes to overcome the negative impact of the reduction in food resources, which is vital to the survival of hooded cranes.

Wintering Behavior of Tundra Swan, Cygnus columbianus, at a Small Water-level Controlled Lake in the Middle and Lower Yangtze River Floodplain

Wintering Behavior of Tundra Swan, Cygnus columbianus, at a Small Water-level Controlled Lake in the Middle and Lower Yangtze River Floodplain

Effects of Human Activities on the Diversity of Waterbirds Wintering in a Shallow Lake of the Middle and Lower Yangtze River Floodplain, China

Human activity is the major factor driving the wetland degradation in shallow lakes. Human exploitation of lake wetlands alters the habitats of wintering waterbirds, and, in turn, waterbird diversity in the shallow lakes. In the present study, we surveyed species composition, abundance, and habitat characteristics of waterbirds in three types of wetland habitats (natural lakeside wetlands, paddy fields, and aquaculture ponds) at Caizi Lake, a shallow lake in the middle and lower Yangtze River during the wintering period, and investigated the effects of habitat change driven by human activity on the diversity of wintering waterbirds. There were significant differences in species composition and abundance among the three wetland habitats (natural lakeside wetlands, aquaculture ponds, and artificial paddy fields); however, there were no significant differences among the habitats with respect to the number of waterbirds. The numbers of overwintering waterbird species and waterbird individuals in aquaculture ponds and lakeside wetlands were significantly higher than the numbers in the paddy fields, indicating that wintering waterbirds prefer natural lake wetlands and aquaculture ponds. Principal component analysis of the three wetland habitat types revealed that factors influencing waterbird diversity include wetland area, vegetation cover, water level, and degree of human interference. Therefore, minimizing human interference and ensuring suitable habitats at specific periods could facilitate the maintenance of waterbird diversity.

Foraging behavior of the Greater White-fronted Goose (Anser albifrons) wintering at Shengjin Lake: diet shifts and habitat use

BackgroundThe habitat use and foraging behaviors of waterbirds are closely related to the distribution and abundance of their food resources. Reductions in food supply can cause waterbirds to shift their habitats and adjust their foraging behaviors to meet their nutritional requirements and increase fitness. Seasonal withdraw of the water levels in the river-connected lakes in the middle and lower Yangtze River floodplain provides abundant food resources for the wintering Greater White-fronted Goose (Anser albifrons). Sedge (Carex) meadows are critical foraging habitats for herbivorous waterbirds in the hydro-fluctuation belt, which changes with hydrological conditions and climate. This study aimed to examine the behavioral responses of the Greater White-fronted Goose to temporal- spatial changes of food availability in the Sedge meadows.MethodsFields surveys were carried out at Shengjin Lake from November 2017 to April 2018. According to the phenology of Shengjin Lake, we divided the wintering season into three periods. The food density, minimum temperature, food items, grass height, and number of foraging geese were surveyed, and samples of the foraging behavior were collected. We analyzed the relationship of the foraging behavior and habitat use relative to the food resources, using correlation and linear regression analyses.ResultsAlong with the temporal-spatial variation and exploitation of food resources, the food abundance and items varied widely among the foraging sites. Over the whole wintering period, the foraging habitat with the highest utilization rate was the meadows, followed by the paddy fields, and then mudflats. Furthermore, the utilization of the meadows showed a bimodal distribution trend, while the paddy fields showed a unimodal trend, and a decreasing trend was seen in the mudflats over the whole wintering period. The results of the generalized linear model showed that the foraging rate was related to the food density and grass height, with a linearly increasing trend during the winter.ConclusionsWith the change of food resources in the three habitats, the habitats used by the Greater White-fronted Geese shifted from meadows in the hydro-fluctuation belt to the paddy fields, and then back to the meadows. The time budget for foraging activities increased correspondingly, and there was an increase in the foraging rate to compensate for food shortages.

Response of Anatidae Abundance to Environmental Factors in the Middle and Lower Yangtze River Floodplain, China

Understanding and predicting animal distribution is one of the most elementary objectives in ecology and conservation biology. Various environmental factors, such as habitat area, habitat quality, and climatic factors, play important roles in shaping animal distribution. However, the mechanism underlying animal distribution remains unclear. Using generalized additive mixed models, we analyzed the effects of environmental factors and years on the population of five Anatidae species: Tundra swan, swan goose, bean goose, greater and lesser white-fronted goose, across their wintering grounds along the Middle and Lower Yangtze River floodplain (MLYRF) during 2001–2016. We found that: (1) All populations decreased except for that of the bean goose. (2) The patch area was not included in any of the best models. (3) NDVI was the most important factor in determining the abundance of grazing geese. (4) Climatic factors had no significant effect on the species in question. Our results suggest that, when compared to habitat area, habitat quality is better in predicting Anatidae distribution on the basin scale. Thus, to better conserve wintering Anatidae, we should keep a sufficiently large area at the single lake, as well as high quality habitat over the whole basin. This might be achieved by developing a more strategic water plan for the MLYRF.

Changing Abundance and Distribution of the Wintering Swan Goose Anser cygnoides in the Middle and Lower Yangtze River Floodplain: An Investigation Combining a Field Survey with Satellite Telemetry

Migratory waterbird communities are quick to respond to ecosystem degradation, and they are widely considered to be important bioindicators of complex environmental changes. The swan goose (Anser cygnoides) has been listed as a globally vulnerable species in the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. This species currently winters almost exclusively in China and is mostly concentrated on lakes in the middle and lower catchment of the Yangtze River floodplain, especially in Poyang Lake, Jiangxi province and some sites in Anhui province. In the past few years, the population of A. cygnoides has fluctuated. To protect this fragile Anatidae species, long-term and accurate population estimation is both necessary and urgent. In this study, we evaluated the change in numbers and distribution of A. cygnoides by comparing surveys conducted in 2004 and 2005 with more recent ones conducted in 2015 and 2016. A reduction in the count number of this species occurred in the survey sites. After a statistical Mann-Whitney U test, the count numbers of A. cygnoides decreased significantly at the survey sites in Anhui province and the abundance decrease at the survey sites in Poyang Lake was only marginally significant. The inaccessibility of the new sites revealed by satellite tracking impeded a more prudent and comprehensive estimate of the population change. Satellite tracking technology may be a tool to consider for increasing the efficiency of data acquisition. Information transmitted from satellite tracking devices can help us to better understand the species’ behavior and wintering habitat. This technology has the potential to substitute costly and time-consuming field surveys. Conservation designs and management plans must be created for specific national nature reserves and key wintering sites. A more efficient long-term species monitoring system with improved spatial coverage should be conducted to safeguard wintering A. cygnoides.

A potential distribution map of wintering Swan Goose (Anser cygnoides) in the middle and lower Yangtze River floodplain, China

BackgroundReliable information on the distribution of target species and influencing environmental factors is essential for effective conservation management. However, ecologists have often derived data from costly field surveys. The Swan Goose (Anser cygnoides), a vulnerable Anatidae species, winters almost exclusively in China’s Yangtze River floodplain, but wintering numbers have been steadily decreasing. To better safeguard this unique species, modern modeling approaches can be used to quantify and predict its suitable wintering habitat. Specifically, a potential wintering distribution map of this species is critically important.MethodsThis study used the maximum entropy approach to model a distribution map of this species. In total, data from 97 up-to-date sites were extracted from 1263 survey sites (excluding duplicate data). After eliminating spatial autocorrelation, 11 environmental variables, including factors related to climate, land structure, vegetation, and anthropogenic activities, were used for model prediction.ResultsThe prediction distribution map shows that the population has concentrated mainly in the boundary area of Anhui, Hubei, and Jiangxi provinces, especially along the Yangtze River. Modeling results suggest that areas within the middle and lower Yangtze River floodplain, such as those in Hunan and Hubei provinces and the eastern coastal area of Zhejiang Province, demonstrate a potential level of “medium” suitability for this species to winter.ConclusionsResults from this study provide fundamental information for the restoration and management of the Swan Goose. Our “visualized” potential distribution map can assist in planning optimal conservation strategies, and consequently may help to increase the number of wintering populations in China.

The relationship between seasonal water level fluctuation and habitat availability for wintering waterbirds at Shengjin Lake, China

SummaryConservation plans for waterbirds in periodically flooded wetlands should be based on a deep understanding of the relationship between habitat availability and the hydrological regime. Using waterbird surveys and remotely sensed images, we investigated how habitat availability for wintering waterbirds was regulated by seasonal water level fluctuation at Shengjin Lake in the lower Yangtze River floodplain, which is an important wintering area along the East Asian-Australasian Flyway. We recorded 52 waterbird species during three field surveys, and categorised them into four groups based on their foraging preferences: grassland, mudflats, shallow water, or deep water. Habitat availability for the four groups was significantly influenced by fluctuations in water level. Habitat for deep-water feeders dominated the lake throughout the year, despite contracting during the wintering season. Water recession during winter exposed more diverse riparian habitats that showed high spatial heterogeneity at the landscape level, with the Upper Lake providing the most suitable habitats for the most diverse and abundant waterbirds. It is worth noting that the water level was regulated highly for aquaculture during the early wintering period, impeding access to suitable habitats for the early-arriving waterbirds that foraged in the riparian mudflats and grassland. Furthermore, rapid water recession from the opening of a sluice gate allowed the exposed moist mudflats to dry up quickly, reducing its suitability for shorebirds and cranes. For effective wintering waterbird conservation in the ephemeral lacustrine wetlands in the Yangtze River floodplain, we suggest stepwise water recession plans, together with the recovery of the aquatic vegetation community and reduction in high-density aquaculture, to synchronise the exposure of foraging habitats with the migration phenology of different waterbird species.

Restriction of Herbivorous Waterbird Distributions in the Middle and Lower Yangtze River Floodplain in View of Hydrological Isolation

Effects of hydrological isolation on species distribution is an active research area in biodiversity protection and management. Lakes in the middle and lower Yangtze River floodplains are irreplaceable wintering grounds for waterbirds on the East Asia – Australasian Flyway. However, more and more lakes in this region have become isolated from the main channel of the Yangtze River and the hydrological connectivity between these lakes and the Yangtze River is deteriorating. This study aims to verify whether herbivorous waterbirds abundance is associated with lake connectivity using synchronous survey data in 23 lakes for the period of 2004–2015. The habitat diversity index, the irreplaceability index and waterbird density were used to evaluate the impact of lake connectivity on herbivorous waterbirds distribution. Our results showed that herbivorous waterbirds distribution was restricted to several better connected lakes although the total numbers of herbivorous waterbird in this region increased over this period. The irreplaceability index of herbivorous waterbirds in connected lakes was significantly higher than that in medium-to-highly isolated lakes. The density of herbivorous waterbirds was lower in highly isolated lakes; but there was an increasing gradient towards the well-connected lakes. Our study demonstrated that hydrological isolation had a significantly negative effect on herbivorous waterbirds.

Hydrological regulation drives regime shifts: evidence from paleolimnology and ecosystem modeling of a large shallow Chinese lake.

Quantitative evidence of sudden shifts in ecological structure and function in large shallow lakes is rare, even though they provide essential benefits to society. Such 'regime shifts' can be driven by human activities which degrade ecological stability including water level control (WLC) and nutrient loading. Interactions between WLC and nutrient loading on the long-term dynamics of shallow lake ecosystems are, however, often overlooked and largely underestimated, which has hampered the effectiveness of lake management. Here, we focus on a large shallow lake (Lake Chaohu) located in one of the most densely populated areas in China, the lower Yangtze River floodplain, which has undergone both WLC and increasing nutrient loading over the last several decades. We applied a novel methodology that combines consistent evidence from both paleolimnological records and ecosystem modeling to overcome the hurdle of data insufficiency and to unravel the drivers and underlying mechanisms in ecosystem dynamics. We identified the occurrence of two regime shifts: one in 1963, characterized by the abrupt disappearance of submerged vegetation, and another around 1980, with strong algal blooms being observed thereafter. Using model scenarios, we further disentangled the roles of WLC and nutrient loading, showing that the 1963 shift was predominantly triggered by WLC, whereas the shift ca. 1980 was attributed to aggravated nutrient loading. Our analysis also shows interactions between these two stressors. Compared to the dynamics driven by nutrient loading alone, WLC reduced the critical P loading and resulted in earlier disappearance of submerged vegetation and emergence of algal blooms by approximately 26 and 10years, respectively. Overall, our study reveals the significant role of hydrological regulation in driving shallow lake ecosystem dynamics, and it highlights the urgency of using multi-objective management criteria that includes ecological sustainability perspectives when implementing hydrological regulation for aquatic ecosystems around the globe.

Selection of a marker gene to construct a reference library for wetland plants, and the application of metabarcoding to analyze the diet of wintering herbivorous waterbirds.

Food availability and diet selection are important factors influencing the abundance and distribution of wild waterbirds. In order to better understand changes in waterbird population, it is essential to figure out what they feed on. However, analyzing their diet could be difficult and inefficient using traditional methods such as microhistologic observation. Here, we addressed this gap of knowledge by investigating the diet of greater white-fronted goose Anser albifrons and bean goose Anser fabalis, which are obligate herbivores wintering in China, mostly in the Middle and Lower Yangtze River floodplain. First, we selected a suitable and high-resolution marker gene for wetland plants that these geese would consume during the wintering period. Eight candidate genes were included: rbcL, rpoC1, rpoB, matK, trnH-psbA, trnL (UAA), atpF-atpH, and psbK-psbI. The selection was performed via analysis of representative sequences from NCBI and comparison of amplification efficiency and resolution power of plant samples collected from the wintering area. The trnL gene was chosen at last with c/h primers, and a local plant reference library was constructed with this gene. Then, utilizing DNA metabarcoding, we discovered 15 food items in total from the feces of these birds. Of the 15 unique dietary sequences, 10 could be identified at specie level. As for greater white-fronted goose, 73% of sequences belonged to Poaceae spp., and 26% belonged to Carex spp. In contrast, almost all sequences of bean goose belonged to Carex spp. (99%). Using the same samples, microhistology provided consistent food composition with metabarcoding results for greater white-fronted goose, while 13% of Poaceae was recovered for bean goose. In addition, two other taxa were discovered only through microhistologic analysis. Although most of the identified taxa matched relatively well between the two methods, DNA metabarcoding gave taxonomically more detailed information. Discrepancies were likely due to biased PCR amplification in metabarcoding, low discriminating power of current marker genes for monocots, and biases in microhistologic analysis. The diet differences between two geese species might indicate deeper ecological significance beyond the scope of this study. We concluded that DNA metabarcoding provides new perspectives for studies of herbivorous waterbird diets and inter-specific interactions, as well as new possibilities to investigate interactions between herbivores and plants. In addition, microhistologic analysis should be used together with metabarcoding methods to integrate this information.

Wintering waterbirds in the middle and lower Yangtze River floodplain: changes in abundance and distribution

SummaryThe middle and lower Yangtze River floodplain is a globally important wintering area for waterbirds in the East Asian-Australasian Flyway. Ornithologists have reported on wintering waterbirds in the floodplain since the 1950s. However, an integrated analysis of the long-term changes in waterbird diversity is not available. Here, we synthesise existing information on changes in wintering waterbird abundance and distribution in the floodplain, summarise possible influencing factors and propose some priorities for further research. Waterbird richness and abundance have declined over the past 60 years. Declining trends have been observed in a number of areas and species. Nevertheless, a few areas and species showed different trends. In addition, waterbirds have become more concentrated in a few suitable areas such as Poyang Lake and Dongting Lake. Land reclamation, hunting, dam operation and extensive aquaculture are probably the four major threats to wintering waterbirds, while establishment of nature reserves is beneficial to waterbird conservation. Our study suggests that waterbirds in the floodplain are vulnerable, and that effective conservation measures are needed to protect and restore the waterbird diversity of this area.

Temporal-spatial patterns of intestinal parasites of the Hooded Crane (Grus monacha) wintering in lakes of the middle and lower Yangtze River floodplain

Parasites have adverse effects on the life and survival of many migratory waterbirds, especially birds on the endangered species list. Hooded Cranes are large migratory colonial waterbirds wintering in wetlands, which are prone to parasite infection, thus monitoring the diversity of parasites is important for sound wetland management and protection of this species. From November 2012 to April 2013, we collected 821 fresh faecal samples from the three lakes (Poyang, Caizi and Shengjin Lake) in the lower and middle Yangtze River floodplain, and detected with saturated brine floating and centrifugal sedimentation methods. Parasite eggs were quantified with a modified McMaster’s counting method. In this study, 11 species of parasites were discovered, i.e., two coccidium (Eimeria gruis, E. reichenowi), five nematodes (Capillaria sp., Strongyloides sp., Ascaridia sp., Trichostrongylus sp., Ancylostomatidae), three trematodes (Echinostoma sp., Echinochasmus sp., Fasciolopsis sp.) and one cestode (Hymenolepis sp.). About 57.7% of the faecal samples showed parasitic infection. All species of parasites were found at the three sites except Hymenolepis which was not found at Poyang Lake. While most samples were affected by only one or two species of parasites, infection by Eimeria spp. was the most common (53.1%). From One-Way ANOVA analysis of the three lakes, parasite species richness index (p = 0.656), diversity index (p = 0.598) and evenness index (p = 0.612) showed no significant difference. According to the statistical analysis of our data, there were no significant difference in parasite species richness index (p = 0.678) and evenness index (p = 0.238) between wintering periods, but a strong difference in diversity index (p < 0.05). Our study suggests that in the wintering Hooded Crane populations, parasite diversity is more sensitive to changes in the overwintering periods than to locations. This also indicates that with the limitations of migration distance, the parasites may not form the differentiation in Hooded Crane populations of the three lakes.