LET someone else shout you down and your partner is more likely to cheat on you鈥攁t least if you鈥檙e a chickadee.
The North American songbirds are largely monogamous and mark their territory by singing. Dan Mennill at Queen鈥檚 University in Kingston, Ontario, played recordings of one male chickadee鈥檚 song in another鈥檚 territory. He found that if he engaged in aggressive song contests by playing the recordings at the same pitch and time as the resident bird鈥檚 song, chicks born later to the male鈥檚 partner were more likely to be fathered by another bird (Science, vol 296, p 873). Mennill says females apparently eavesdrop on how well their mates fare in song contests, and if he loses, she becomes more promiscuous.
