The New Kids on the Block may sound terribly dated, but strains of Jingle Bells conjure holiday spirit year after year. Now, researchers have found a similar phenomenon in bird culture. Male chestnut-sided warblers (Dendroica pensylvanica) sing two kinds of songs—one that attracts females and another that challenges rival males to a turf war. Both songs are considered culture because they're transmitted from one generation to the next by learning. But they're evolving at very different rates. For 19 years, researchers recorded the warblers in a Massachusetts forest and found that the courtship tunes  hardly changed—perhaps because female birds reject new variations. The fight songs , however, had no such restrictions. Among dozens of versions of the song, no rendition stayed in vogue for more than 7 years, and most disappeared after just 1 year, the researchers will report  in the October issue of The American Naturalist. Anthropologists have observed the same pattern of change in human baby names and pop songs—a parallel that hints that birds may provide clues to how human culture evolves.
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