Fairy Wren Passwords

Mother fairy wrens teach their chicks passwords while they're still in their eggs to tell them from cuckoo impostors:

She kept 15 nests under constant audio surveillance, and discovered that fairy-wrens call to their unhatched chicks, using a two-second trill with 19 separate elements to it. They call once every four minutes while sitting on their eggs, starting on the 9th day of incubation and carrying on for a week until the eggs hatch.

When Colombelli-Negrel recorded the chicks after they hatched, she heard that their begging call included a single unique note lifted from mum's incubation call. This note varies a lot between different fairy-wren broods. It's their version of a surname, a signature of identity that unites a family. The females even teach these calls to their partners, by using them in their own begging calls when the males return to the nest with food.

These signature calls aren't innate. The chicks' calls more precisely matched those of their mother if she sang more frequently while she was incubating. And when Colombelli-Negrel swapped some eggs between different clutches, she found that the chicks made signature calls that matches those of their foster parents rather than those of their biological ones. It's something they learn while still in their eggs.

It's worth noting that this is primarily of use to the chicks' parents, so they know not to expend time and energy on the impostor cuckoo chick. Cuckoo chicks, as part of their evolutionary adaptation, kick the real chicks out of the nest, so they're lost in any case. It's the fact that the signal allows the parents to identify impostors and start a new brood that's of evolutionary advantage.

Additional articles.

Posted on November 12, 2012 at 1:03 PM • 8 Comments

Comments

Frank WilhoitNovember 12, 2012 4:11 PM

Correlate this with the finding a couple of years ago that parrots give their chicks names in the shell. The difference is that parrots do not face this particular problem. Perhaps, in this context, we are imputing a motivation to the behavior based on our preconceptions of why cuckoos so what they do; whereas it may actually be a bird-universal, if anyone took the trouble to check other orders?

Dirk PraetNovember 12, 2012 6:30 PM

Which then of course begs the question: why don't they move on to next logical step, which is kicking out the cuckoo chicks that fail to properly identify themselves ? I guess this deserves a prize for security theatre in the wild.

CanarioNovember 12, 2012 6:35 PM

Maybe the calling repeater is just to check how many chicks are still alive and warm from those "in bad bio-shape" so that heat can be "uniformly distributed" in the incubation process. By re-arranging egg's for instance.

Spaceman SpiffNovember 12, 2012 7:19 PM

I just goes to show, "It doesn't serve to try and fool Mother Nature"! :-)

In any case, perhaps we should sing more to our children when in the womb, so we can better know them, and they, us!

ChromatixNovember 13, 2012 4:18 AM

The advantage for the wren, more precisely, is that they can avoid the enormous cost of feeding the impostor chick until it becomes independent. If they no longer hear the password, they can abandon the impostor, and build a new nest and brood.

So it's a mitigation strategy rather than a prevention strategy - a set of airbags and crumple zones instead of power steering and anti-lock brakes.

AdamNovember 13, 2012 10:07 AM

Seems like an imperfect solution but evolution is blind so it can't determine which way its going or alter course except through advantages or disadvantages that mutations confer on the offspring.

Perhaps one particular bird started chirping to its egg and the response from the chick made the adult expend more effort to raise it and the trait survived. A bit like how a human is more likely to bond with a baby that gives a big gummy smile over one who doesn't react at all.

And it reached the point that birds who don't get the response tend to abandon their chicks more frequently and in the process abandon cuckoo chicks which means they are more likely to reproduce again and pass and increase the trait.

PaulNovember 14, 2012 7:28 AM

Sent a link to the story to a birdwatching friend - He wrote,

Fairy wrens are little jewels. Unfortunately, North American warblers and other small passerines have not had evolutionary time to develop such a defense adaptation against the Brown-headed Cowbird, also a brood parasite, since its spread across NA has occurred only since the cutting off of the eastern deciduous forest in the past 200 years.

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