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♦ ¹How Important are Columnar Cacti as Sources of Water and Nutrients for Desert Consumers? A Review, B. O. Wolf and C. Martínez del Rio, Isotopes Environ. Health Stud., 2003, Vol. 39(1), pp. 53-67
♦ ²del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona.