The list of things that only humans can do is constantly shrinking. Here’s an unexpected item to cross off: nepotism. Researchers say African desert birds will push their stepsons out of the group while promoting their biological sons to positions of power. They published their findings in the journal Biological Letters.

The southern pied babbler (Turdoides bicolor) is a dapper-looking little bird that makes its home in the dry savannah of the Kalahari Desert. The babblers are social birds, but their idea of socialization looks less like a tea party and more like a tense happy hour for high-level executives and their staff. Like many animals, they live in groups with strictly delineated social hierarchies. Each group includes a dominant male leader; his preferred in-circle of other dominant males; subordinate males; and dominant and subordinate females. All the birds in these units raise chicks together, which means that at any given time, the male leader may be looking after some other dude’s kids.

In many animal societies, subordinate members lose out on certain privileges. They may have to wait to eat until everyone else has eaten, or they may not be allowed to reproduce. Researchers were curious about the effect of babblers’ hierarchy on its subordinate members. They compiled 11 years’ worth of observations on color-banded babblers living at the Kuruman River Reserve and coded the birds’ behavior. 

Things are getting a little tense in the babbler household. Image Credit: Martha Nelson-Flower

The researchers found that over time, subordinates could become dominant, but only if they stuck it out and stayed with the group. But the ability to stay seemed to be a privilege afforded mostly to the biological sons of dominant males. Subordinates living under their stepfathers’ rule were more likely to be pushed out, which meant they’d have to go be subordinate somewhere else. Interestingly, female birds were completely uninvolved in these familial power struggles. To them, babies were babies.

Lead author Martha Nelson-Flower is a postdoctoral fellow at the University of British Columbia. She notes that the strained dynamics of blended families are part of what makes babblers who they are. "Nepotism has likely played a vital role in the evolution of family life in this species," she said in a press statement.

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