Male peacocks have tail feathers that make up about 60% of their body length. during the mating season they shake these feathers in front of females. longer feathers produce a larger volume of rustling sound for a given shaking rate, but they are also heavier, and thus require more energy to shake at a given rate than shorter feathers. this suggests that:

Feather length is a compromise between the conflicting selective pressures against too long or too short of a tail

Explanation:

Tail or feather length is a trait in peacock that is a random trait and do not depends upon any other trait. Now as mentioned in the question, shaking off tall feathers  requires more energy by male peacock than short feather. This indicate a selective pressure of tall feather over short feather that will help the peacock having shorter feather to lessen the energy requirements.

The short feathers can also e considered as an evolutionary adaptation of female peacock to lower the energy requirements of their body.

Hope it help!

a time line cause it goes from 685 to 978

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