The bluebird is an aerial predator that circles above the creatures. A strict carnivore, it will carry off isolated babies and piles of meat. Bluebirds will not land or attack anything within a one tile range of adult creatures, so never leave babies unattended.
Since they never land, bluebirds cannot be killed.
For a child to be "protected", a creature has to meet certain requirements. A creature with two to three gems must be adjacent to a child to protect it from the Bluebird.
A Bluebird can be detected by a hawk-like screeching sound, similar to how a carnivore can heard by a low growling. A shadow is visible on the ground, but to spot the bird itself, zoom/scroll(F key) outwards to spot it. They resemble a hawk with a black beak, yellow eyes, and blue feathers as seen above.