Ecologist: Before finding a mate, male starlings decorate their nests with fragments of aromatic plants rich in compounds known to kill parasitic insects. Since these parasites are potentially harmful to nestlings, some researchers have hypothesized that the function of these decorations is nestling protection. However, males cease to incorporate such greenery once egg laying starts, which suggests instead that the function of the decorations is to attract females. Which one of the following, if true, most strengthens the support for the ecologist's conclusion? ['Nestlings grow faster in nests that incorporate aromatic plants than in nests that do not.', 'Male starlings tend to decorate their nests with a greater number of aromatic plants when a caged female is positioned adjacent to the nest.', 'The compounds in the aromatic plants used by the male starlings to decorate their nests are harmless to nestlings.', 'Male starlings do not decorate their nests in areas with unusually small populations of parasitic insects.']