Mutated birds, the ones that swarm you during the moon event have some pretty odd interactions with mechanics such as freezing and fire.
For whatever reason they appear to be immune to both being frozen and being set on fire, as well as any other fire damage.
They're also immune to being put to sleep oddly enough too.
They also walk straight through walls.
On the chance this is intentional I'd like to have it looked into being changed as its quite limiting on potential options for fighting off the swarms and makes the fights very linear.
Start moon storm event, aid in Wagstaff's quest and wait until the swarm appears.
Notice how they're able to walk through walls and are immune to sleep and elemental effects/attacks.