14 DAY TRIAL // From fish to humans, hormones govern responses to courtship signals. A new study of bird songs suggests they influence the way the auditory system processes the signals. In other words, hormones change the way birds listen to courting songs at certain times of the year.
Like many other animals, songbirds stage their reproductive songs and dances each spring: Male birds perform their finest songs, and female birds dance, propped up by their hormones. The dance is called "copulation solicitation". Neuroscientist Donna Maney from Emory University examined the auditory areas of the brain to see how estrogen affects the genes expression induced by the song. This process of turning the genes on is called "genomic response".
"Our work suggests that estrogen, which is normally high only during the breeding season, may actually alter auditory pathways and centers," Maney says. "The changes in gene expression reflect changes in the brain that are related to auditory learning and attention."
Maney and her research group compared estrogen-treated female white-throated sparrows with females not treated with hormones. The birds then listened to recordings of either seductive male song or synthetic, frequency-matched beeps. While the hormone-treated birds reacted to the songs of the seductive males and started to dance, the other ones remained largely indifferent at both types of sounds.
But the result was more interesting: "The main difference between estrogen-treated and untreated birds was not that estrogen increased the response to song. Rather, estrogen decreased the response to beeps. This decrease could be a mechanism for tuning out what is not relevant, allowing the birds to focus on the signals important for breeding," Maney says.
She added that these experiments belong to a wider context of various studies indicating how hormones affect sensory processing in general. "Our results fit with studies showing that women's preferences for masculine faces, voices and body odors change over the menstrual cycle, as hormones are changing," she said. "What we've started to uncover here is a possible neural substrate for such hormone-induced changes."