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Scientists are trying to better understand how some baby birds are given up for adoption. To be more precise, some birds give up their eggs, leaving them for others to raise. Scientists who study this have a long tradition of using a bit of deception. They plant fake eggs. And now they're taking that practice high-tech with the rapidly expanding technology of 3-D printing. NPR's Nell Greenfieldboyce has this encore presentation.
NELL GREENFIELDBOYCE, BYLINE: There are some tricky birds, like cowbirds and cuckoos, that lay their eggs in the nests of other species. Sometimes, the eggs get accepted. Sometimes, they get tossed out of the nest. Biologist Mark Hauber studies cowbirds at Hunter College in New York. He wants to know, what is it about a speckled cowbird egg that makes it either acceptable or not?
MARK HAUBER: It could be the size. It could be the speckling itself or the lack thereof. And it could be the color, beige versus robin blue.
GREENFIELDBOYCE: Since the 1960s, scientists have used fake eggs to test birds' reactions to all these different things, partly because real eggs from wild birds are hard to come by.
HAUBER: Instead of using natural eggs, it's best to use fake eggs because you can control the size, the shape and the color much more accurately.
GREENFIELDBOYCE: He remembers his first fake egg.
HAUBER: In 1997, I went into a craft store and bought a beige, speckled egg, which looks very much like a cowbird egg.
GREENFIELDBOYCE: It was actually an Easter decoration. But most of the time, Hauber and other scientists can't just go into a store and buy the perfect artificial egg. They have to make eggs for experiments by hand, using wood or plaster of Paris or clay, and then painstakingly paint them. Hauber says all of this is not his forte.
HAUBER: I'm a terrible craftsperson.
GREENFIELDBOYCE: He says his plaster eggs are awful.
HAUBER: They look like pears instead of eggs.
GREENFIELDBOYCE: So when affordable 3-D printers became available, Hauber thought, great, these machines take 3-D computer models of an object and then create that object out of plastic. Hauber bought one and tested its ability to print a fake egg.
HAUBER: I loved it. It had the shape of a cowbird egg because we designed it as such. It had the weight of a cowbird egg and it was standardized across hundreds of hundreds of eggs that we have printed.
GREENFIELDBOYCE: They've now published a study in the journal PeerJ showing that robins, at least, treat the printed eggs like real cowbird eggs. They throw them out of the nest. Christie Riehl is a bird biologist at Princeton University. She was impressed by this study because it used a whole range of fake cowbird eggs, from small round ones to long skinny ones.
CHRISTIE RIEHL: It would be really labor-intensive to individually handcraft eggs that exploit that whole range of variation. And it would be very difficult to find commercially available eggs - like, even wooden eggs or something - that would have the properties of size and shape they you're trying to test.
GREENFIELDBOYCE: She speaks from experience. She's made dozen of eggs the old-fashioned way. She's excited by the potential of this technology, not just for fake eggs but all sorts of knickknacks for experiments.
RIEHL: With 3-D printing, it's the possibility of being able to make exactly what you want. And not only that, but you can share those designs with other researchers so they can replicate your results with exactly the same method.
GREENFIELDBOYCE: The printed eggs aren't perfect yet. The colors aren't great. Scientists still have to paint them. And while Hauber has been able to print hollow eggs, the plastic shells are currently too strong to be pierced by a bird's beak. That's important because piercing an egg is how some species get rid of it. Hauber is now dreaming of somehow making a pierce-able egg, maybe out of sugar.
HAUBER: I did see a way of how cooks make fake eggs and fill it with ice cream that comes with a very fragile shell. So I might try that technique.
GREENFIELDBOYCE: But he's also still trying to do it with his 3-D printer. Nell Greenfieldboyce, NPR News. Transcript provided by NPR, Copyright NPR.