Prenatal learning: Not just for humans. Researchers studying the embryos of superb fairywrens, Malurus cyaneus, have discovered that these little songbirds can distinguish between different birds while still in ovo. The findings were published in Proceedings of the Royal Society B this week.
Traditionally, embryos and their immature, developing brains are thought to have only limited learning abilities. Not so anymore. Human neonates show plenty of behaviors that indicate prenatal learning and even individual recognition. Around 32 to 34 weeks, human fetuses start responding to their mother’s voice. From then on, they start distinguishing male from female voices and their mothers’ from that of strangers. This is called prenatal acoustic discrimination.
A 2012 study led by Sonia Kleindorfer from Flinders University showed that, superb fairywren hatchlings successfully solicit more food by incorporating the vocal password they learned from their mothers while still in the egg during late stages of incubation. That way, the parent birds know they’re feeding their own babies -- and not parasitic cuckoo chicks.
Now, Kleindorfer and colleagues wanted to test if superb fairywren embryos can discriminate between different acoustic stimuli. Using an iPod and a yo-yo speaker, they played minute-long recordings to 43 eggs in nests found in wildlife sanctuaries and conservation parks in South Australia. The eggs ranged in age from nine to 13 days (they typically incubate for about two weeks). There were three different types of recordings: superb fairywren female incubation calls, contact calls of the neighboring winter wren, and white noise (as a control).
All the while, the team measured the embryonic heart rate response using a digital egg monitor that tracks light absorption changes of the eggshell due to blood flow. A lowered heart rate is a physiological correlate of attention. They aren't "moving as much, trying to stay quiet, trying to be attentive," Flinders University’s Diane Colombelli-Négrel tells National Geographic.
Fairywren embryos, they found, lowered their heart rate in response to the broadcasts of same-species calls and calls from a winter wren -- but not to the white noise. During the period afterwards, their heart rates remained lowered in response to fairywren calls but not with winter wren calls or white noise. It’s a sign that they were learning to discriminate between the calls of a different species and those of their own, Science explains.
Additionally in further trials, the embryos also lowered their heart rate in response to the calls of new superb fairywren individuals they’ve never heard before -- and not when they heard the familiar bird from the earlier tests. They responded more to the call of the unfamiliar bird, showing how they can recognize vocal characteristics of individuals.
Images: Sonia Kleindorfer