In the womb, human babies can recognize mom and dad's voice, and it was thought until recently to be the only species with such an ability. But new research found that bird embryos inside eggs can do the same thing.
Research published in the journal Proceedings of the Royal Society B detailed how superb fairy wrens, an Australian songbird, listen to calls while developing inside their shells and as a result learn a "password" from its mother that it will later use to beg for food.
"Thus, fairy-wrens join humans as vocal-learning species with known prenatal learning and individual discrimination," the study authors wrote.
Just how were scientists able to determine the birds were listening to calls from their kind?
National Geographic explained that the researchers hooked up the eggs to a heart rate monitor. A lower heart rate in human fetuses has shown that they are more attentive to what's going on in their surroundings. The researchers in this study made the same assumption with birds.
The scientists then exposed the bird embryos to the call of an adult fairy wren and white noise. Heart rates were lower when the bird was calling compared to the white noise. Eventually, the researchers found the birds became used to the sound of one wren and introduced a new wren call. With the new call, they saw the birds' heart rates drop again as they were learning the new sound.
"The fact that they are learning in the egg is very impressive," Robert Lickliter with the Florida International University in Miami, who was not involved with the study, told National Geographic.
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