The Shiny Cowbird (Molothrus bonariensis) is an avian brood parasite that could represent a threat for the survival of some endangered birds. To evaluate this potential problem for threatened or endemic wetland species, we estimated the abundance of Molothrus bonariensis and studied its behavior, its association with vegetation and its interspecific interactions in 19 wetlands located in the Bogotá area, Colombia. We found densities between 0 and 2.24 ind./ha, which are significantly lower than those of the Yellow-hooded Blackbird (Chrysomus icterocephalus), a known host. Urban wetlands presented higher cowbird densities than semiurban and rural wetlands together. The cowbirds showed a strong association with introduced trees between 10.1 and 15 m high, isolated from other trees and with medium foliage densities, as well as with stands of bulrush. Only 4.5% of the cowbirds observed were interacting with individuals of other species, mostly the blackbird, which sometimes evicted the cowbird from its territories. We conclude that the abundance of Molothrus bonariensis may not yet represent a serious threat for most species it parasitizes with the exception of Apolinar’s Wren (Cistothorus apolinari), which is in such a precarious situation that the presence of only a few cowbirds could be disastrous for its persistence.