My first guess is he has worms. If hes eating and drinking fine. its very common but you need to treat him fast.... and the rest of the flock too.
I use Levasole. Ivermectin is good for most parasites... but not everything. Use the levasole now... then in 2 weeks use ivermectin....
Retreat every 6 months.
Here is some information we have on the United Peafowl assoc. chat forum.........
Peafowl Wormers Dosage/Duration
Wormer Trade name capillaria cecal roundworm tapeworm
Albendazole 11.36% Valbazen yes yes yes yes 0.40cc/lb, oral drench down the throat
Fenbendazole 100mg/mL Safe-Guard or Panacur 10% yes yes yes yes 1) 3cc/gal water for 3 days. Can repeat in 10 days.
2) 1cc (bird over 1 year), drench down throat for 3 days
3) 1/2cc (bird between 3 mos. and 1 year) oral drench
down throat for 3 days.
Ivermectin Ivomec for cattle no yes yes yes 1) 3cc/gal drinking water for 24 hours
2) 1/2cc (bird over 6 mos.) given as subcutaneous shot
or as drench down throat.
3) 2/10 cc (bird under 6 mos.) given as subcutaneous
shot or as a drench down throat.
Levasole, 52 gm packet Levasole, 52 gm packet yes yes yes no Mix I packet with 1 gallon water.
Mix 1 teaspoon of above solution with 1 gallon drinking
water. Treat for 3-4 days.
Tramisol, 13 gm packet sheep drench, 13 gm packet yes yes yes yes Mix one packet with one quart water; mix two
Tablespoons of this solution per gallon drinking
water. Treat for 3-4 days.
Levasole for hogs, 500cc plastic bottle yes yes yes yes 1) Fill the bottle of Levasole with water; shake well.
Mix 1 teaspoon of this solution per gallon drinking
water. Treat for 3-4 days.
2) Mix 1/4 teaspoon of the powder from the bottle
per gallon of drinking water. Treat for 3-4 days.
* Note: Fecal sample is required for accurate diagnosis.