Cuckoo birds have evolved a nasty habit of laying their eggs in the nests of other bird species, who then unknowingly tend to their young. But as new research published in Current Biology reveals, the fairy-wren has developed a rather ingenious countermeasure: Expectant mothers teach their unhatched offspring a secret password that they'll later need to get fed. The cuckoo chicks, who don't know the password, are out of luck.
There are many aspects about this discovery that are fascinating.
First, it's remarkable that fairy-wrens have evolved a mechanism to thwart Horsfield's bronze-cuckoo parasitism in this fashion. For a trait to evolve like this shows just how versatile and exploratory nature can be when confronted with a problem. But given how detrimental brood parasitism is to the host bird's reproductive fitness, it shouldn't come as a surprise that evolution found a way.
And as the researchers correctly point out, it's a tactic that borrows from meme theory — the notion that ideas, and not just genes, can get passed down from generation to generation and used in an adaptive way. In this case, the meme is a signature element found in a one-note chirp.
Moreover, these memes — what are essentially passwords — are taught to the chicks while they're still in their eggs (what's called prenatal learning) during late incubation. So, by the time they hatch, the fairy-wren chicks already know what to ‘say' in order to prove that they're the real deal (and not a cuckoo chick). If the mother doesn't hear the proper "solicitation song," she will simply refuse to feed the chick.
And fascinatingly, if the entire nest is overrun by cuckoos (or chicks who don't know the proper password), she will abandon the nest and move on to start again. Yikes.
The researchers, a team led by Sonia Kleindorfer of Flinders University in Australia, also noticed that mother fairy-wrens will teach the password to other caregivers of her young, including mates and other helpers. When they do this, however, they're out of earshot of the chicks. Which is smart.
Kleindorfer also noticed that the signature element varies from nest to nest; all passwords are unique and tied to a particular mother. Cross-fostering experiments confirmed that a fairy-wren mother will not feed a genuine fairy-wren chick if it doesn't know the password.
The entire study can be found at Current Biology.
Top image: Shutterstock/Katarina Christenson. Inset image via.