When Brains Beat Bonds: How Chickadees Choose Smarter Mates

Female mountain chickadees usually live with one partner and care for their young. They stay near a nest and help feed chicks. But they sometimes mate with other males when a smarter male is nearby. This behavior is called extra-pair mating.

Researchers tested birds with 'smart' feeder arrays to measure spatial memory. About a third of the offspring sampled were sired by extra-pair males, and 70% of nests had at least one extra-pair young. Males with better spatial memory sired more extra-pair young and fledged heavier chicks. The work was done over three breeding seasons in the wild. The birds live in the Sierra Nevada mountains.