Soul of Flight

Wyverns die in open sky and the drop stays at the exact height it appeared, with nothing to pull it down. If the kill happened above your screen or inside a floating island you can fly straight past the pile and never see it. Fight them against open sky where you can see what falls, and sweep back through the airspace afterward rather than assuming an empty screen means an empty drop.

They only spawn near the top of the map, so the setup is a small platform up in the clouds with a light on it and some patience. They are long and segmented, and the drop appears wherever the head ended up, which is often well away from where you were shooting.

Once you have the wings you actually intend to wear, surplus souls are worth more converted than raw. A finished pair sells for far more than the parts that went into it, so run the spares through whatever wing recipes you have unlocked before you visit a merchant.