Passage Summary: Male birds put nice-smelling plants in their nests. Some think it's to kill bugs that hurt babies, but because the males stop doing it once the eggs are laid, an ecologist thinks it's actually just a way to impress females.

Conclusion: The aromatic plants used by male starlings are intended to attract mates rather than to protect the nestlings from parasites.

Reasoning: Male starlings stop adding these plants to the nest as soon as the females begin laying eggs.

Analysis: The ecologist's argument hinges on the timing of the behavior. If the plants were for 'nestling protection,' you would expect the males to keep adding them when the nestlings are actually present and vulnerable. To strengthen this, we need to further decouple the plants from the health of the babies. Look for an answer that shows the parasites are actually most dangerous or prevalent *after* the males stop adding the plants; this would make the 'protection' theory look very unlikely and leave 'attracting females' as the more plausible explanation.