Knowledge about the sex ratio within an animal population is important to predict population dynamics, and to understand the relative arrival times of males or females at wintering grounds, and sex ratio allocation strategy (Donald, 2007; Shao et al., 2012a; Clausen et al., 2013).
In general, the juvenile proportion of the Swan (Cygnus spp.) ranges from 10% to 30% during wintering period across the species' range (Rees et al., 1997; Huggins, 2009; Beekman and Tijsen, 2015).
In this paper, we monitored the sex ratios of four species of waterfowl (Common Teal Anas crecca, falcated duck Anas falcata, mallard Anas platyrhynchos, and Eurasian wigeon) and the age structure of one species of waterfowl (Tundra Swan Cygnus columbianus) wintering at Poyang Lake, Jiangxi Province, China.
The objectives of this study were a) to identify variation in the sex ratios in four duck species, and the age structure of Tundra swan in Poyang Lake; b) to estimate the time arrival at wintering grounds and departure from wintering grounds of waterfowl species of both sexes at various age stages; and c) to understand and predict future population dynamics in the above mentioned species.
In western Europe, the main wetlands that support wintering waterfowl are found along the coastal areas of Denmark, the Netherlands, United Kingdom, France (the Rhone delta), Spain, and northern Italy.
The population-weighted overlay of individual waterfowl species' ranges intersecting with HPAI H5N1 virus locations (Figure 2B) can, in turn, be intersected with the wintering areas' boundaries (rescaled from 0 to 1 as an index of wintering site suitability) to delineate the areas where migrating birds are more likely to concentrate.
First, as well as being along flyways of infected wild bird, establishment of HPAI H5N1 virus in domestic poultry may require additional conditions: 1) an aggregation of waterfowl for a sufficient period (more risk for transmission within wintering areas than at more transient stopover sites), 2) a high proportion of small poultry farms and backyard poultry, and 3) extensive (aquatic) poultry units in contact with waterfowl populations and habitat, i.e., floodplain or other forms of wetland agriculture in close proximity to natural wetlands used as wildfowl wintering sites.
acuta, have large wintering concentrations in and near Lake Chad and in the Niger delta, both under the western Siberia/Black Sea flyways, and are presumed to be infected by HPAI H5N 1 virus.
However, the researchers found that mates in 7 of 10 pairs of birds with known wintering
locations arrived within 3 days of each other, even though these mates typically wintered 1,000 km from each other.
Robinson of the University of Illinois at Urbana-Champaign points out that the study "certainly indicates there isn't enough good habitat" for wintering