What is the control group in this experiment?

A scientist believes that bright red chest coloring on male birds makes them more attractive to females. In an experiment, she uses six birds, all with the same color chest. She bleaches the feathers of two of the birds, dyes the chests of two of the birds bright red, and leaves the chests of two of the birds alone. When females are exposed to these males, she believes that more females will chose to mate with the red-dyed males.|||Check out:





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I would say that the control group is the two birds left alone, but I think one could make the argument that the bleached ones are included too. A control is supposed to be a sample that only differs from the test group in the characteristic being studied. The purpose of the bleached birds is not clear from the question since the researcher does not give any hypothesis about them.