Some time after the creation of the bloodthorn tree, a local species of bird began to live in them. Through natural evolution, the bird developed a symbiosis with the tree. The bird learned to use the tree's poison in its own defence. The bloodthorn bird's nests are made exclusively of bloodthorn twigs, a fact which would make the nest self-defending in itself. However, with the placement of the nest within the bloodthorn's branches, the tree itself is also used as a defence against nest predation.
Due to their proximity, the bloodthorn's berries have become a staple in the bloodthorn bird's diet. The bird will injest the berry and its droppings contain seeds. Not all seeds carried this way are viable, but enough have survived to allow the bloodthorn to expand its boundaries faster than wind and gravity would be able to spread the seeds.