Why do European long-tailed tits help feed related young after their own nests fail?

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Serengeti National Park, Tanzania: herd of gnu (wildebeests) — Animal social behavior Herd of gnu (wildebeests) in the Serengeti National Park, Tanzania.

European long-tailed tits that have experienced nest failure often assist in feeding the young of other birds. This behavior is a classic example of kin selection, a process where individuals increase their inclusive fitness by helping relatives survive and reproduce.1

Because these birds share a significant portion of their genes with their kin, helping related young ensures that some of the helper's own genetic material is passed on to the next generation, even if the helper's own nest has failed. This aid-giving behavior is explained by Hamilton’s rule, which posits that such altruistic actions can evolve when the indirect fitness benefits gained by supporting relatives outweigh the costs the helper incurs by sacrificing its own immediate reproductive efforts.1