A pair of fairy wrens are in our garden – their calls are shrill, sweet and curiously penetrating. And for the first time ever, I think they might stay. This is terribly exciting. When we moved here eight years ago, we transformed a backyard of kikuyu grass into a small tangled oasis of native plants, deliberately planted thickly to entice small birds. Our street has mostly old-style Brisbane yards: mowed lawn with the odd tree or shrub, and the birdlife is dominated by magpies, butcherbirds, and the local gang of noisy miners.
Now two drab little fairy-wrens, a female and a non-breeding male, are hopping from twig to twig in our backyard. They pounce on insects as they go, trilling almost continuously. Shouldn’t they hush? The neighbourhood bully-birds will surely hear them, and chase them away. But maybe the fairy-wrens’ need to keep in contact with each other (and perhaps share a lively conversation about this new place) outweighs the risk of being detected? After all, a fairy-wren’s song helps it to survive while still a naked babe in the nest, and it learns its first call while still in the egg.
Female superb fairy-wrens sing to their eggs, while sitting in the nest. This seems like an odd thing to do, as calling from the nest would make it more obvious to predators, and also to cuckoos who regularly parasitise fairy-wrens. Are their advantages of singing on the nest that outweigh the risk of attracting predators and parasites?
To find out, researchers in South Australia¹ recorded the song of female fairy-wrens on the nest, and also recorded the songs of the chicks. They noticed that each mother had a slightly different call. But what was even more fascinating, was that the begging calls of chicks included song elements that were most similar to the calls of the mother wren. By swapping eggs between nests, they showed that the chick’s calls were not inherited genetically, they were learnt. The chicks were learning how to sing from the female wren who reared them.
But, as suspected, some of eggs were eaten by predators – especially currawongs and ravens. Horsfield’s bronze cuckoos had been active too, surreptitiously leaving their eggs in some fairy-wren nests. But that’s when things started to get really interesting.
Over a series of experiments and observations, the researchers discovered something astonishing. The fairy-wren chicks were learning the mother’s call while still in the egg. And when they hatched, the chicks that could mimic the mother’s call most faithfully were the ones that received the most food. Chicks that sung the mother’s song poorly, or not at all, received less food.
Cuckoos were unable to learn the fairy-wren mother’s call while developing in the egg. Once hatched, the cuckoo chick had to learn very quickly how to imitate the fairy-wren begging call. If it didn’t learn to modify its call quickly enough, it would be abandoned by the fairy-wren parents, even if it was the only chick left in the nest. So the lullabies sung by the mother fairy-wren over her eggs turned out to be vital to the survival of her chicks.
The more the female fairy-wren called to her eggs, the higher the similarity between the chicks’ and the mother’s calls. The female fairy-wrens also called to their eggs more often when a cuckoo call was heard near the nest. Male fairy-wrens also learnt the begging call from the female fairy-wren, and would preferentially feed the chicks who gave the correct begging call. Song-learning before hatching has been demonstrated for all other fairy-wren species that have been studied.
So as I listen to the fairy-wrens singing in my garden, I wonder if I’m hearing song phrases that were learnt while still in the egg. Perhaps these little birds have stayed together and survived this far – across the suburban wasteland – because they understand the importance of song for their survival. I can only hope that the female will one day sing lullabies of life over her own eggs, from a nest hidden deep in the scrubby nether regions of our yard.
Colombelli-Négrel, D., Hauber, M. E., Robertson, J., Sulloway, F. J., Hoi, H., Griggio, M., & Kleindorfer, S. (2012). Embryonic learning of vocal passwords in superb fairy-wrens reveals intruder cuckoo nestlings. Current Biology, 22(22), 2155-2160.
Kleindorfer, S. (2015) The ecology of embryonic learning: costs and benefits of vocal tutoring in fragmented habitat. Presentation at the Ecological Society of Australia Conference, Adelaide.
This article was reprinted in the June 2016 edition of Australian Birdlife.