WASHINGTON -- The love life of a female chickadee could make a country music classic: "If your song don't pass muster, buster, I'm gone."
The lady chickadee has a cheatin' heart, quick to find another lover if her mate fails to win his daily song contests with rivals. In effect, she decides that if her mate is a loser, he won't be the only papa in her nest, say researchers at Queen's University in Kingston, Ontario.
Daniel Mennill, co-author of a study in the journal Science, said mates of high-ranking male black-capped chickadees are more likely to be unfaithful than are the mates of lower-ranked males.
"Females are accustomed to hearing their high-ranking mates dominate a song contest," said Mennill. "It is quite a shocking event to their ears to hear them lose a song contest."
When that happens, he said, the female will sneak out before dawn and meet with a rival male for a coupling. Then she flies back home as if nothing happened and continues to live with her partner.
"These extra matings are just short copulations -- about 30 seconds," said Mennill. The long-term partners "do remain mated, in a social sense."
The effect of these extra matings is that some chicks in the nest have been fathered by some other male chickadee, he said. And the betrayed male apparently never knows the difference.
Mennill said he established by DNA analysis of blood from the chicks that one or two birds per clutch had some other father than the one that raised them.
A daily contest
Male chickadees are challenged virtually every day to a song contest with rival males. They use the contests to defend territory and nests.
"It is only the males that sing," said Mennill. "Every male chickadee has only one song -- two notes that sound like 'fee-bee."'
One male sings and the other then sings back in a competition that may last for several minutes.
"If a male is very aggressive, he'll go through a set of routines where he will match the pitch and try to overlap the song of his opponent," said Mennill.
While this is going on, the female is listening, gauging who is winning. If her mate loses, she remembers.
Mennill proved the chickadee cheating by recording some of the bird songs and then engaging in a singing contest with a male bird.
"The main effect is that the female is more likely to engage in extrapair copulations if the high-ranking partner was bested," he said.
The females of high-ranking males are most likely to cheat, he said.