MINERAL METABOLISM IN A BLACK-NECKED SWAN (CYGNUS MELANOCORYPHUS) POPULATION FROM SOUTHERN CHILE M. Cecilia Norambuena, Ph.D. and Francisco Bozinovic, Ph.D. Abstract: A population of black-necked swans (Cygnus melanocoryphus) residing in a perturbed habitat revealed a low body mass, malnutrition, and hyperferremia during 2005; the swans main dietary item, Egeria densa, was lost during an environmental crisis which occurred in 2004. The objective of this study was to monitor the diet and nutritional status of this population during 2006, as well as to verify how the consumption of sediment, as part of their new diet, may explain the mineral disorders observed in these birds. Results revealed that swans increased their body mass and had an adequate protein, lipid, and iron metabolism, in spite of the fact that they maintained the same new diet (sediment and roots) during 2005–2006. In addition, transferrine saturation was indicative of the high endogenous iron load in birds which agrees with the high iron load of their environment. On the other hand, the consumption of the Cayumapu River sediment in the diet (25%) did not affect the body mass nor the nutritional and hepatic function in domestic geese over a 45-day period. Key words: Biochemistry, black-necked swan, Cygnus melanocoryphus, hematology, iron metabolism. INTRODUCTION Although human activities induce profound changes in landscapes around the world, the ecologic and physiologic consequences of these changes are not well understood for many of the species occupying these altered habitats. 2,3,22 Heavy metal poisoning has been related to sediment consumption in free-living waterfowl populations, including swan populations. 1,6,11 The black-necked swan (Cygnus melanocory- phus, Anatidae) is an herbivorous aquatic bird endemic to South America. 10,23 Recently, in 2004, the Carlos Anwandter Nature Sanctuary (SA- NAT-CA, Ramsar, Chile), which was the major breeding area for this species in South America, underwent a major environmental disturbance. The event was related to chemical changes in the local water due to effluents originating from a new cellulose plant in the area. 17,24 As a result of this environmental disturbance, the main aquatic plant Luchecillo (Egeria densa), disappeared almost completely from the 4,700 ha of the ecosystem, and nearly 3,000 swans emigrated from the sanctuary. The occurrence of these swans’ morbidity and mortality (ca. 200 swans) was associated with emaciation, parasitism, and hemochromatosis. 8,9 It was suggested that iron overload was probably related to the new diet composition of the birds. 8,9 A year later, the Cayumapu River swan population (at SANAT- CA) still had malnutrition and a lymphopenic, hyperphosphatemic, and hyperferremic condi- tion. 19 Although it was determined that the swan population shifted from ingesting Egeria densa to eating underwater roots mixed with the local sediment, no differences were noted in the chemical quality of the new diet (roots) and the previous diet. 19 The objective of this study was to monitor the diet and nutritional status of the Cayumapu River swan population during 2006, as well as to evaluate the effect of the consumption of the Cayumapu River sediment on the health and nutrition of anseriform birds. Beyond the local scale, the role of sediment consumption as a source of heavy metal poisoning in free-living bird population was also investigated. MATERIALS AND METHODS Study site The field study was carried out along the last 4 km of the Cayumapu River (39u359S, 73u189W) prior to its emptying into the Carlos Anwandter Nature Sanctuary (SANAT-CA), Chile. This swan population has historically been included with that of censuses of the SANAT-CA, given its proximity, and this site was included within the Cruces River National Reserve Project. Diet and nutritional status of Cayumapu River swans Ten male, adult, black-necked swans were captured in December 2006 by hand-netting from From the Center for Advanced Studies in Ecology and Biodiversity and Departamento de Ecologı ´a, Facultad de Ciencias Biolo ´gicas, Pontificia Universidad Cato ´lica de Chile, CP 6513677, Santiago, Chile (Norambuena and Bozinovic); and the Facultad de Agronomı ´a e Ingenierı ´a Forestal, Pontificia Universi- dad Cato ´lica de Chile, CP 6904411, Santiago, Chile (Norambuena). Correspondence should be directed to Dr. Norambuena (mcnoramb@puc.cl). Journal of Zoo and Wildlife Medicine 40(4): 617–623, 2009 Copyright 2009 by American Association of Zoo Veterinarians 617