While walking through the mysterious swamp, Aang, Katara, and Sokka stopped to make camp. As Sokka tried to convince the group that it was just a normal swamp, a nearby screech from this bird frightened them, and they huddled together to quell each other's fear.
Later, when Team Avatar was having dinner, another screeching bird landed nearby and, after letting out its awful scream, was swatted away by a tree root.
The screeching bird has white or light gray feathers that appear to be puffed up all around its body. Its eyes and beak are almost hidden by its pudgy face; the eyes especially appear beady and dark beneath its head feathers. Though its beak appears very tiny when closed, it can open very wide to emit a loud shriek that sounds like a woman screaming.
The bird does not really seem to have any real world connections beyond its appearance as a bird, although its terrifying shriek may have been inspired by the call of the real-life spot-bellied eagle-owl, or perhaps the similarly-named screech owl.