Who would've known that an egg could be made entirely of solid ice? These eggs start out rather transparent and thin, to the point where one could see a silhouette of the fetus inside. As the creature inside grows, the "shell" thickens and gradually becomes opaque.
Parfridge require freezing cold temperatures in order to healthily develop. It's not uncommon to see Parfridge mothers coating their icy offspring in snow to ensure they stay as cold as possible. Parfridge nests, hidden deep within evergreen trees, only ever seem to appear in the most blizzard-ridden parts of the island.
Parfridge hatchlings are a rather odd case. The eggs don't truly "hatch" per say, but the ice around the egg at hatching time slowly morphs into a shape that can only be described as a combination of bird and snowman. Inside this shape is the baby Parfridge, safely growing out of harm's way. How a Parfridge hatchling keeps itself sustained whilst sealed within thick ice is currently unknown, but it's been theorized that the surrounding ice has special properties and the bird absorbs vital nutrients from it.
Eventually, when it has become much more bird-shaped, the ice will suddenly begin to melt away. This is the nearly adult Parfridge emerging from its frozen casing, ready to spread its wings and roam around the wintry lands of Southern Ark.
A curious quirk of the adult Parfridge is that its internal temperature is always sub-zero. Parts of its plump body will very frequently freeze over forming shining ice crystals all over it. Just like their egg form, Parfridge require these temperatures in order to stay healthy—if a Parfridge was ever removed from the Coldworld, it could potentially perish without adequate care.