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Effects of El Niño Southern Oscillation on Numbers of Black-Necked Swans at Río Cruces Sanctuary, Chile

Roberto P. Schlatter, René A. Navarro and Paulo Corti
Waterbirds: The International Journal of Waterbird Biology
Vol. 25, Special Publication 1: Proceedings of the Fourth International Swan Symposium 2001 (2002), pp. 114-122
Published by: Waterbird Society
Stable URL: http://www.jstor.org/stable/1522341
Page Count: 9
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Effects of El Niño Southern Oscillation on Numbers of Black-Necked Swans at Río Cruces Sanctuary, Chile
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Abstract

Population trends of Black-necked Swans (Cygnus melancoryphus) at Río Cruces Sanctuary are analyzed and discussed in light of annual and seasonal fluctuations at this Ramsar site. Aerial, boat or ground surveys of swans have been made every month since 1985. Pronounced annual and seasonal fluctuations in numbers, with lows during the wet autumn/winter and peaks during the dry spring/summer, characterize this population. Numbers of swans more than doubled during the La Niña periods of 1989-1991 and 1996-1997. These periods coincided with macro-regional droughts that forced swans to move nomadically in the southern cone of the Neotropic. Río Cruces is a stable wetland and a likely demographic source for Black-necked Swans in the region, where their distribution and numbers have increased in the last decade.

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