The Montezuma oropendola (Psarocolius montezuma) is the largest member of the blackbird family found in Central America (Gupta, 2001; Webster, 2003).  Montezuma oropendolas are highly frugivorous, although they also eat a wide variety of invertebrates and small vertebrates (Levee, 1988; Loiselle, 1988; Webster 1997). The Montezuma oropendola has a unique social system, as it is one of only a few bird species that exhibits female-defense polygyny (Webster, 1994a).  Bird mass is highly influenced by sexual selection, and this bird is one of the most sexually size dimorphic of all bird species (Webster, 1997).  Female-defense polygyny is attainable within the Montezuma oropendola because 1) males do not engage in parental care, 2) females nest in aggregations, and 3) females breed asynchronously within the colony and synchronously within a cluster (Webster, 1994a). In order to avoid predators such as arboreal mammals, Montezuma oropendolas prefer to nest in large trees not connected to the continuous forest canopy (Skutch, 1954). Still, these oropendolas are greatly susceptible to brood parasitism by the Giant Cowbird (Webster, 1994b). There is some support to suggest that brood parasitsm by the Giant Cowbird selects for nest clustering within colonies, which in turn facilitates the defense of female aggregations by a single male (Webster, 1994b).