SAT Inferences Question

Carolina chickadees are cavity nesting birds that initiate nest building at the same time of year as golden paper wasps, a species that also nests in enclosed spaces. Researchers observed that both species will settle in nesting boxes, but birds and wasps are not often observed co-occupying boxes, leading to the hypothesis that the two species compete for nesting sites. To test this hypothesis, the researchers installed nesting boxes throughout a nature preserve in the US state of North Carolina, manipulated some of the boxes to exclude birds, and then monitored the boxes for two years. Not only was the hypothesis validated, there was also a clear indication of competitive advantage for birds. Which finding from the study, if true, would most directly support the text's characterization of the study's results?