Passage Summary: Scientists think that when male birds puff up their neck sacs for females, they are actually showing off how healthy they are.

Conclusion: The courtship display of inflating air sacs is a mechanism for female sage grouse to identify healthy mates.

Reasoning: Male sage grouse only reveal and inflate these hidden neck sacs during their spring courtship rituals for females.

Analysis: To strengthen this hypothesis, we need to find a direct connection between the physical state of the air sacs and the actual health of the bird. If the display is a 'test' for health, then a sick bird should presumably have a display that looks different or less impressive than a healthy one. Look for an answer that shows a correlation between the condition of the air sacs and the presence of parasites or disease. If the sacs look the same regardless of health, the scientists' theory would be in big trouble.