Which bird is a symbol of peace?

The dove, and doves and pigeons are the same family - the difference is entirely one of connotation, not biology. The bird released from the ark in Genesis, returning with an olive leaf, is the source of the image, and Picasso's lithograph for the 1949 World Peace Congress fixed the modern version of it.

The bird itself is not notably peaceful. Doves are territorial and will fight persistently, and Konrad Lorenz's observation that a caged dove can peck another to death over days - where a wolf will not kill a rival that submits - was one of the founding anecdotes of ethology. The symbol is about the story, not the animal.

Their real distinction is navigation and, uniquely among birds, milk. Homing pigeons find their way over hundreds of kilometres using a combination of the sun, the Earth's magnetic field, and smell, and carried messages in both world wars - one, Cher Ami, delivered a message that saved a trapped American battalion in 1918 after being shot through the chest. Both parents also produce crop milk, a protein-rich secretion fed to the young, which almost no other bird does.