Friday, November 9, 2012

"What's The Magic Word?" (And No, It's Not 'Please')

If you think you've got it bad studying for an upcoming exam, researchers found that young fairy wrens are also expected to learn- but these fairy wrens are learning while still in the egg. Should they fail to do so, they won't just be given a bad grade- instead, their mother may refuse to feed the hatchlings, or their parents may abandon them altogether.

A young fairy wren's next meal, it appears, is dependent on their retention of a song taught to them as an embryo. Sonia Kleindorfer, a researcher at Flinders University, initially began recording fairy wrens to identify anti-predator calls. While the wrens were being recorded, however, she noticed that fairy wren mothers were singing to their unhatched eggs. She also noted that after hatching the begging calls of fairy wren chicks matched the song their mothers had sung to them before hatching, and that the learned songs varied between nests. She eventually realized that the fairy wren mothers were teaching their offspring a unique note, or 'password', with the expectation that after hatching they will have retained that password and be able to reproduce that particular note. 

Typically, after fairy wren eggs hatch, the parents provide for their young by bringing food back to the nest. As the mother wren returns with dinner the nestlings clamor for food by chirping out begging calls. Before the female feeds the nestlings, however, they must repeat the same note which they were taught while still inside the egg, allowing the mother to identify the nestlings as her own. If the note goes unrecognized, the nest is abandoned and the nestlings are left to fend for themselves.

A superb fairy wren ('superb' isn't being used as an adjective here- the superb fairy wren is the species of fairy wren which Klinedorfer and her team were studying.) Image credit: Wikipedia

It's not that mama wren doesn't love her children; rather, the 'password' is an evolutionary adaptation to the threat of being parasitized by other birds. By teaching their embryonic offspring a unique learned note, fairy wren mothers ensure that they will not be tricked into caring for the hatchlings of other parasitic bird species. Fairy wrens in particular are prone to deceit by neighboring cuckoo birds. Parasitic cuckoo bird mothers often lay their eggs in a fairy wren's nest, liberating themselves from the responsibility of having to raise, feed, and care for their own offspring. Although they are similar in appearance, cuckoo bird eggs hatch before true fairy wren eggs, and the young cuckoo birds push the unhatched fairy wren eggs out of the embryo. The duped mother wren would then unknowingly give up her time, energy, and valuable resources in caring for the cuckoo bird's offspring if the deceit was never spotted.

A female cuckoo bird. Image credit: Animal Planet/Discovery.com

To confirm that the 'passwords' were learned and not genetic, Kleindorfer swapped the eggs of 22 nests with other fairy wren eggs before the embryos were 'taught' by their mothers. The  newly hatched fairy wrens mimicked the song of their foster mothers and not their biological mothers, indicating that the song had been learned by the embryo as a direct result of the adult's communication. There also appears to be a learning curve: when a fairy wren mother repeats her song more frequently, her offspring produce a better mimic of the song. Additionally, when Kleindorfer and her team played foreign begging calls at the nests, neither parent fed the fairy wren chicks.

 Even so, fairy wrens only retaliate against the duplicity of parasitic cuckoo birds by abandoning the nest approximately 40% of the time, a number which has varied throughout the years. While the 'password' method is far from perfect, it is a unique approach to counteracting the threat of cuckoo bird parasitism and implies that young fairy wrens are able to learn from their parents even as embryos. So even if you can't teach an old fairy wren new tricks it seems that you can teach a young embryo new songs, a feat which is far more impressive.

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