Life Sucks When You're On the Wrong Side of Bird Nepotism

Southern pied babblers only want to take care of their own.
August 26, 2016, 3:54pm
Southern pied babblers. Image: Wikimedia Commons/Derek Keats

Some people work hard to become successful, and some are just born successful. Birds are no different.

Southern pied babblers are the nepotists of the avian world, according to ecologist Martha Nelson-Flower. After spending five years observing the charismatic species, she noticed that males exhibited "evil stepdad" behavior, ensuring the survival of their genetic material. Her findings, which were published this week in Biology Letters, tell a cut-throat tale of sexual competition in the African desert.

Evolutionarily speaking, these birds have done alright. Southern pied babblers, or Turdoides bicolor, are widespread across savannas in southern Africa, and are a species of "least concern." Much of their success comes from "cooperative breeding," in which "helpers" raise the chicks of a male and female breeder. In terms of survival, this type of social structure can reduce predation and strengthen territorial claims. But, as Nelson-Flower discovered, it also has its drawbacks.

"Nepotism has likely played a vital role in the evolution of family life in this species," said Nelson-Flower, who is now a postdoctoral fellow at the University of British Columbia's faculty of forestry, a statement.

During her time in the Kalahari Desert, Nelson-Flower studied 45 groups of southern pied babblers. She noticed that in most of these groups, subordinate males would spend less time with their family if they were unrelated to the dominant male. Sometimes, their stepdads would even force them out of group. And while biological offspring could quickly rise into the ranks of "breeder," outsiders spent more time as "helpers" before ascending up the social chain, if at all.

To humans, this probably seems diabolical, but even lowly stepsons get something out of the deal. If forced out of the family unit, young males may die. However, by remaining in the service of the breeding pair, they have a chance to one day pass on their genetic lineage.

This type of behavior isn't unheard of among cooperative breeders, but it is the first time it's been systematically documented among the African species. According to the study, Nelson-Flower believes that nepotism helps to ensure the fitness of the group by allowing subordinates to inherit the dominant position, should the alpha male die.

"The research is some of the first to show that the sex of both dominant and subordinate birds, and the genetic relationship between them, has a significant impact on their family groups and cooperative breeding behaviour," Nelson-Flower added.

Cooperative breeding is poorly studied in birds, and ornithologists aren't entirely sure what long-term benefits it serves. Some theories suggest it's a form of altruism, though southern pied babblers would likely be an exception to that rule.

Maybe birds of a feather really do flock together.