How do animals adapt their senses to their surroundings? This has fascinated scientists for years, and it turns out that experiences growing up and as an adult play significant roles. Vocal communication is an essential part of social interaction in many animals, including humans – consider how a child learns to speak and respond to their parent's voice, forming strong bonds through communication by voice. But how important is it for female zebra finches to hear male voices when they are young? Can they still form a preference for their partner's trills as adults if deprived of hearing the songs of males as youngsters? Sarah Woolley and Erin Wall at McGill University, Canada, chose zebra finches to find out. Zebra finches are sociable songbirds where the males learn to sing and the females listen closely to their songs to learn how to recognise them, choose mates and form lasting partnerships for life.
Wall and Woolley allowed some female zebra finch chicks to grow up with both parents, hearing their father's songs as well as their mother's voices; however, the fathers of other female zebra finch chicks were removed from their cage, so those chicks grew up without hearing the songs of other male birds. Once the chicks had grown up, the duo paired the young adult females with males for 2 weeks in the hope that they would form a lifelong partnership, and, sure enough, they did, regardless of whether they had heard male voices as they grew and developed. Females from both home backgrounds formed stable relationships with their male partners, constructing nests and generally settling down, even though some had not heard a male voice through the time they were growing up. So, it is not necessary for a female to hear a male voice while growing up to be able to form a partnership with a male for life as a young adult.
Next, the duo tested the females’ preferences for their partner's songs, allowing them first to select between their male’s courtship serenade and the courtship song of unfamiliar males, before checking whether the females were particularly attracted to the courtship serenade of their partner. Sure enough, after 2 weeks of cohabiting with her new partner, each female was particularly partial to his trills, regardless of her upbringing, and were more keen on courtship calls than general conversation, even when the singer was just some random male. Living with a male and bonding is enough to make his song attractive, regardless of their early life experiences.
However, while the couples were developing their relationship over the 2 weeks of the experiment, the researchers also allowed female/female couples to listen in on the conversations of the newly forming couple to find out whether simply listening to the songs of an adult male, without seeing or interacting with him, would allow the females to develop a strong preference for his utterances. However, it did not; females develop a strong attachment to the serenades of their partners and not just any male singing in the vicinity.
So, it seems that even without listening to the songs of adult male zebra finches early in life, adult female zebra finches form life-long partnerships and preferences for male song. It's living with a male while forming a life-long attachment that makes his serenade more desirable. However, being deprived of male voices early in life does appear to affect the females’ nesting behaviour, with the females that had been deprived of male song as youngsters spending less time on their nests toward the end of the 2 week bonding period, suggesting that the lack of male song early in life may possibly have delayed breeding.
