An investigator went to Central America to study oropendulas, which are communal nesting birds. Anor species of bird, cowbird, sometimes lay its eggs in nests of oropendulas. Some of populations of oropendulas throw cowbird eggs out of nest, and some dont. The investigator was interested in finding out why some birds would raise or species as ir own but ors would toss m out. By watching nests closely, he found that blowflies lay ir eggs in nests of oropendulas, and that young larvae, maggots, feed on young birds. If young cowbirds are in nest, precocious cowbirds eat  blowfly larvae, protecting young oropendulas. In colonies of oropendulas that discriminate against cowbirds, throwing m from  nest, blowflies are not eaten by cowbirds. These colonies of oropendulas build ir nests close to a particular wasp colony, and wasps eat blowflies.
The relationship between oropendulas that discriminate against cowbirds and  cowbirds is one of