The Chilean Mockingbird (Mimus thenca) serves as the primary vector for transmission of mistletoe (Tristerix aphyllus) to its cactus host (Echinopsis chilensis) in Chile. A small proportion of the cactus population is parasitized by the mistletoe, and the behaviors of mockingbirds and the physical defenses of the cacti both contribute to the concentration of the parasitic mistletoe on those plants. Plants with longer spines are visited less frequently by the mockingbirds and are less likely to receive mistletoe seeds. In turn, plants parasitized by mistletoe are more frequently visited by mockingbirds, and mistletoe becomes aggregated on a subset of the cactus population. This photograph originally appeared on the cover of Ecology (85:1) in January of 2004.