The South African bulbul

“He who knows when he can fight and when he cannot will be victorious.” – Sun Tzu, The Art of War:

Some battles aren’t worth fighting. The rewards of victory are too small or the costs of combat are too high. Good generals know this, and so does evolution. The natural world is full of intense arms races between predators and prey, hosts and parasites. If one side evolves a small advantage, the other counters it with an adaptation of their own, and both species are locked in an ever-escalating stalemate. But sometimes, these arms races never take off. The costs of engagement just aren’t worth it.

Oliver Kruger from the University of Bath has found one such example in South Africa, where a small local bird called the Cape bulbul is plagued by the Jacobin cuckoo. Like many other cuckoos, the Jacobin is a “brood parasite”, an animal that relies on others to rear its young. It lays its eggs in a bulbul nest, palming off its own young to unwitting surrogate parents.

Cuckoos and their hosts are usually excellent examples of evolutionary arms races.

The cuckoo and the bulbul: