Birds are valuable study organisms for understanding the evolution of complex traits, especially those that involve learning. They have relatively short generation times for a vertebrate, and are easily studied both in the wild and (for some species) in the laboratory. This presentation will describe two studies that show how complex traits that involve learning can evolve by natural selection. First, the village weaverbird has distinctive eggs in Africa, in order to tell when a parasitic cuckoo lays eggs in its nest. After the weaver was introduced to islands without cuckoos, however, they lost some of the distinctiveness of their eggs, and became less able to discriminate against foreign eggs. In the other case study, male swamp sparrows sing songs of repeated notes. Faster songs are harder to sing, and females like them better. These birds learn their songs during a narrow time window as juveniles. Lahti and his partners brought nestlings into the laboratory and trained them on songs that were experimentally slowed relative to their natural rate in order to see how well birds would learn these lower performance-training models. Swamp sparrows memorized the training models regardless of their speed, but they demonstrate two kinds of unlearned and adaptive biases during development: they speed up slower songs, and they reproduce faster songs more accurately. Both of these studies show how inheritance and learning interact to produce the final form of a behavior.

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