What do the modified feathers of a wild turkey serve as?

The modified feathers of a wild turkey play a significant role in attraction for mates. During the breeding season, male wild turkeys display their plumage extensively as part of their courtship rituals. The vibrant and iridescent feathers, particularly found on their tail and body, are crucial in conveying health, vitality, and genetic fitness to potential female partners. The way these feathers are arranged and presented can attract females when males spread their tail feathers into a fan shape, showcasing their coloration and size, which are indicators of their desirability as mates.

This primary function of the modified feathers in mate attraction highlights the importance of sexual selection in the evolution of these birds' physical traits. While insulation, camouflage, and flight are also critical functions of feathers in general, the specific context of the wild turkey's modified feathers being used to attract mates is what makes this option the most accurate in the context of the question.