Answer:
If the females start to use criteria other than the color of the feathers when choosing a partner, there would be a decrease in the variations of red tones. Thus, the variation in these tones would not be an advantageous feature.
Step-by-step explanation:
The variation in the red tones of these birds allows the males with the most vibrant and striking red feathers to be considered as ideal mating partners. If females use different criteria to choose a reproductive partner, the red color variability in the male's feathers would no longer be an advantageous feature for them. For this reason, this variability would gradually decrease, until it was completely eliminated from the population of these birds.