Brood parasites are organisms that rely on others to raise their young. For example, the cuckoo will lay its egg in nests belonging to the Reed warbler seemingly with the intent for the warbler to hatch and feed the cuckoo hatchling. Scientists have wondered how the parasitic cuckoo chick gets fed because other studies have shown that it takes stimulation of multiple open beaks—either sight or sound—to compel a mother warbler to provide food.
Researchers observed that the parasitic chicks have bright yellow patches on the ends of their wings and they make those patches quiver when the host parent returns to the nest. Researchers hypothesized that the bright yellow patches on the ends of the cuckoo's wings were related to stimulating the feeding process.
Which of the following procedures is NOT consistent with their hypothesis?