Cooperative breeding is when three or more individuals contribute to the care of young. While this happens in many animals, it is the social system of approximately 9% of birds, and is particularly prevalent in sub-Saharan Africa and Australasia.
However, understanding why evolution drove such behaviour remains controversial. Some studies have linked its occurrence with variable and unpredictable environmental conditions, while others have linked it to stable and predictable conditions.
We thought it might have something to do with defending their nests against brood parasitism, a behaviour where other birds to raise your babies. Brood parasitism is most easily recognisable among cuckoo birds, who never build their own nest or raise their own offspring. Instead they lay their eggs in the nests of birds from other species, and leave the substantial task of raising their chick to the unsuspecting host.