Changes in the Abundance and Distribution of Black-necked Swans (Cygnus melancoryphus) in the Carlos Anwandter Nature Sanctuary and Adjacent Wetlands, Valdivia, Chile

Abstract

Abstract. Recently, the Carlos Anwandter Nature Sanctuary (Sanctuary) at the Cruces River, Chile, has undergone important ecosystem changes. Brazilian waterweed (Egeria densa), the main food resource of Black-necked Swans (Cygnus melancoryphus), has greatly decreased in abundance. This disappearance may have affected the abundance of Black-necked Swans within the Sanctuary; however, the variation in the Black-necked Swan population is still poorly understood. Spatiotemporal variation in population abundance and feeding/breeding ecology of Black-necked Swans was analyzed in the Sanctuary and adjacent wetlands (non-protected areas outside the Sanctuary) from 2000 to 2010. Temporal fluctuations in Black-necked Swan abundance were recorded, with increases in population size from late December to early June and decreases from late June to late September. Five main feeding grounds that were devoid of Brazilian waterweed were identified. However, several other aquatic plants were recorded on these grounds, sugge...