Probably working on their harmonies: Zebra finches are smart birds, partly because their learning starts while they are still in the egg, including distinguishing their parents' song from other birds. Adwo/Shutterstock

Playing music to children while they are still in the womb to increase their intelligence may be more than a scam to attract money from prospective parents. Although its validity has yet to be confirmed in mammals, a new paper shows songbird embryos can recognize their parents' songs while still in the egg, and develop their brains accordingly.

The idea that birds can be influenced by sounds while in the egg remains a controversial one among scientists. Dr Mark Hauber of the University of Illinois told IFLScience, “We've been fighting...with other avian neurobiologists” over the question of whether birds can even process noises from outside the shell. “They have always assumed that embryonic songbirds (or even young nestlings) do not have good enough hearing to perceive songs and calls of even their own parents,” Hauber said.

Hauber's latest work goes way beyond this, however. Not only does he claim in NeuroReport that unhatched birds can tell the difference between birdsong and silence, he even claims they can distinguish between the songs of their own and other species.

With several co-authors Hauber primed unhatched zebra finches by collecting them from their nests on the day of laying and playing them recorded birdsongs or silence for 30 minutes a day while incubating them. The brains of the birds were examined for expression of the ZENK gene, which Hauber told IFLScience can be measured using the density of radioactive staining specific to the expressed gene.

By comparing expression in the part of the brain associated with auditory processing and in a non-auditory area, the team was able to confirm any ZENK increase was related to sounds. In other words, not only do the birds hear the songs and respond, but their brains develop as a result.

Birds exposed to birdsongs showed stronger ZENK expression than those that heard only silence, the authors report. Moreover, the expression was stronger among the birds who were played songs from their own species, compared to those who got fairywrens' greatest hits.

Hauber has recently published work showing exposure to songs before hatching helps male finches win mates as adults by improving the speed with which they learn to sing. Another study in 2016 suggested finch parents sing songs to their eggs that help them prepare for things like a warming climate. Fairywrens also appear to use the calls they learn before hatching to improve their capacity to beg food from their parents afterward, so the findings make evolutionary sense

Of course there is a big difference between a bird being able to hear through thin eggshells and a human fetus through the walls of the uterus and the mother's body. However, Hauber told IFLScience the evidence brains are capable of processing complex sounds before birth is consistent with previous studies on humans, and we may benefit from a rich sonic environment in the womb.