Temporal and spatial use of resources by black swans (Cygnus atratus) on the Vasse-Wonnerup wetlands

Zoë Kissane

Black swans are large herbivorous waterbirds with a dietary preference for submerged aquatic plants. They are endemic to Australia and are known to be opportunistic in their use of habitat. The largest regular breeding colony of black swans in the south west of Western Australia occurs in the Ramsar listed Vasse-Wonnerup wetlands. Although home to large numbers of waterbirds, it is a highly eutrophic and modified system and little is known about the effect of water management decisions on waterbird ecology. Therefore, the aim of this study was to determine the main drivers of temporal and spatial black swan abundance over an annual cycle, and the seasonal composition of black swan diet. Seasonal swan counts were conducted (5 counts per season; in all seasons) across ten sites, where abundance, activity and use of habitat were recorded. To determine seasonal composition of swan diet, faecal samples were collected in all seasons and analysed using microscopy and molecular genetics (DNA). Results showed there was a significant difference between both regional (F4,80 = 11.02, p< 0.001) and seasonal swan abundance (F3,80 = 80.11, p< 0.001), with mean swan abundance highest in winter (n=2073) and spring (n=1960) (summer n=245; autumn n=360). The proportion of plant material in swan faecal matter varied seasonally, with macrophytes found in greater proportions to other plants in spring (X2/4 = 67.75, p < 0.001). In contrast, Lamprothamnium macropogon and samphire plants were found in higher proportions than all other plants in autumn (X2/4 = 101.32, p < 0.001) and winter (X2/4 = 28.06, p < 0.001). Lamprothamnium macropogon and salt marsh plants such as samphires are important components of black swan diet, particularly in the absence of submerged aquatic plants. These results have important implications for wetland management, because they show the importance of fringing salt marsh vegetation for swan populations. As salt marsh habitat is a threatened ecological community, these results emphasize the importance of protecting this vegetation, not just at this site but the Swan Coastal Plain and Australia more broadly.

Temporal and spatial use of resources by black swans (Cygnus atratus) on the Vasse-Wonnerup wetlands

Files and links (1)

Abstract

Details

UN Sustainable Development Goals (SDGs)

Metrics