How the con artist cuckoo finch begs off parenting
The cuckoo finch has evolved to dupe other birds into raising its young. A team of researchers have discovered another adaptive strategy that the cuckoo finch has employed.
When a cuckoo finch lays its eggs, it does so in another bird’s nest. And not just one egg, quickly atoned for with an apologetic, “Oops, I didn’t mean to put that there.” No, the cuckoo finch plops multiple eggs into another bird’s nest, bedding them with the put-upon bird’s own eggs.Skip to next paragraph
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“The better to trick their hosts,” says Claire Spottiswoode, a researcher at the University of Cambridge and a co-author on a new paper published this week in Nature Communications.
Cuckoo finches are adroit freeloaders, nesting their eggs with another bird’s eggs in hopes of the besieged bird wasting its time and food on bringing up babies that it mistakes for its own. It also now unfolds that these Frank Abagnales of the bird world are more savvy than previously thought.
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It turns out that placing more than one egg in another bird’s nest, as opposed to just one egg, is an adaptive move that improves the cuckoo bird’s odds of foiling the selected foster parent, according to new research from a team of British ecologists working in Choma, Zambia. The insight helps to tell the tale of the cuckoo finch’s long, evolutionary pas de deux with the bird on which it begs off its young, each of them two-stepping through time – sometimes leading, other times following – in hopes of outwitting the other.
The cuckoo finch is a parasite, but it does not look like one – or, at least, not like a parasite as it is often imaged, as a microscopic critter fringed with uncomfortable numbers of legs. Fluffed and puffed in yellow-brown feathers, the female cuckoo finch is a squat but regal bird, like a plump princess. The male bird, not to be outdone, is DayGlo gold.
The cuckoo finch is not at all related to the cuckoo bird (though some cuckoo groups also practice parasitism). In fact, it is out on what Dr. Spottiswoode calls an “evolutionary limb,” some 20 million years removed from its closest relatives, the indigobirds and the whydahs, both of the Viduidae family of African bird parasites.
Brood parasitism – that is, foisting one's young on un-expecting parents – is believed to have evolved seven different times in birds. About 100 different species of birds practice it (about one percent of known bird species). It is also common practice among insects, as well as fair game for some fish, including the so-called Cuckoo Catfish (Synodontis multipunctata). This fish manages to get its eggs into the mouth of another species of fish in Africa’s Lake Tanganyika; the fraudulent eggs then hatch into fish that eat the mother’s own babies – all inside her mouth.
In other words, cuckoo animals (also known as “strange” animals) are ruthless little con artists. And brood parasites, as a group, present to ecologists a list of compelling questions, as tangled as the branches on an evolutionary tree: How did these dupers evolve to pull off their ruses? And, as the host animals adapt to shake off their parasites, how do they manage to keep doing it?
Well, what is known is why animals do it: “brood parasitism is a great strategy if you can get away with it,” says Spottiswoode. “If your offspring require care to develop and grow, and you as a parent can fob off the costs of providing such care onto someone else, you can save the energy that parental care would otherwise consume – and rather spend it on producing more offspring.”
But to get away with it, an animal must be good – Bernie Madoff good. And the cuckoo finch is that good.
Cuckoo finches hoodwink at least three different Cisticola species, as well as the Tawny-flanked Prinia. These are not the most stunning birds, especially relative to the gold-wreathed cuckoo finch. Cristicolas are pale brown (but with proud, primped chests) while the Prinia is as common looking as birds come: small and, in an avian insult, mousy brown.
But the birds do lay some of the prettiest eggs in the proverbial basket: blue with splotches and squiggles; red-brown and pink-brown and pinkish-red; white and cream and olive green.
So, to trick the Prinia and the Crisicola birds into raising cuckoo finches as their own, cuckoo finches must replicate this rainbow suite of eggs. To do so, each female cuckoo finch specializes in imitating the eggs of just one kind of host bird. That’s an already incredible feat, as it’s not quite clear how a female cuckoo finch manages to keep laying one egg design, even after breeding with different males (in fact, little is known in general about how genes control for egg color).