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Lua i Stíl Chicago (17ú heag.)Calvert, William H., Martin B. Hyatt, agus Norma P. Mendoza Villaseñor. The Effects of Understory Vegetation on the Survival of Overwintering Monarch Butterflies, (Danaus Plexippus L.) in Mexico. Instituto de Ecología, A.C, 1986.
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