Changes in the abundance and distribution of Black-necked swans (Cygnus melancoryphus) in the Carlos Anwandter Nature Sanctuary and adjacentwWetlands, Valdivia, Chile

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, suggesting that these areas provide alternative food resources for Black-necked Swans. Changes in the reproductive timing of Black-necked Swans throughout the 10-year study were recorded; no reproductive events occurred between 2004 and 2006, and a shortened reproductive period occurred between 2006 and 2010. In addition, there were changes in the locations of the breeding grounds as well as in the number of nests and chicks recorded during the study period. These results revealed new patterns in Black-necked Swan population trends as well as their distribution in areas both inside and outside the Sanctuary. Thus, to ensure effective conservation of this species requires the integration of protected areas within as well as non-protected areas outside the Sanctuary.