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

Abstract

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.

Combining Tracking and Remote Sensing to Identify Critical Year-Round Site, Habitat Use and Migratory Connectivity of a Threatened Waterbird Species

“…However, Poyang Lake also continues to suffer severe multiple environmental pressures. These include sand dredging [41], increased shipping activity, habitat loss, upstream damming and pollution of catchment water quality by industry and agriculture, as well as being under constant threat of hydrological damage from the construction a major dam to isolate it from the main Yangtze River [42][43][44]. Interrogation of thousands of satellite images using machine learning algorithms identified 1092 vessels extracting sediments within Poyang Lake, illegal activities that are reshaping water channels and profoundly adversely impacting upon wintering swan geese (Anser cygnoides) another endemic Chinese wintering waterbird species that increasingly relies on the site for its winter quarters as numbers decrease elsewhere [45,46].…”

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

“…Due to soil erosion and sedimentation, a large area of the lake has transformed into a mudflat. Polders were constructed at the lake from the 1960s to 1970s to establish paddy fields to address a major shortage in arable land in the region [19]. At the end of last century, the growth of the crab aquaculture industry led to the transformation of large areas of lake wetlands into aquaculture ponds, which reduced the area of natural wetlands in the region considerably ( Figure 1).…”

“…Among these factors, vegetation and benthic organisms represent key factors influencing habitat choice of birds in wetlands [43]. Water levels influence food availability, and, in turn, waterbirds' distribution in different types of wetlands [19]. In addition, increasing human interference in the form of activities such as fishing and grazing [44] drive waterbirds to migrate to different habitat fragments.…”

“…Shallow lake wetlands at the middle and lower Yangtze River floodplain are important wintering and stopover sites for the migratory waterbirds on the East Asian-Australasian flyway [18]. Every year, large numbers of waterbirds winter and stop at these sites, which are important aggregation sites for globally-migratory waterbirds [19,20]. The sites are also under the influence of human activities.…”

“…The sites are also under the influence of human activities. The degradation and shrinking of many natural lake wetlands in the region and their transformation into artificial wetlands in the form of paddy fields and aquaculture ponds [19] has altered the habitats for waterbirds and could affect waterbird diversity.…”