From prosthetics and toys to jet engines and refrigerator parts, 3D printers have the potential to revolutionise the production of pretty much everything. But the technology has recently gone wild, quite literally, with experiments producing the first ever 3D-printed mock bird eggs.

Scientists have long wondered why some birds accept foreign eggs in their nests from brood parasites – birds like cuckoos, cowbirds and cuckoo finches that don’t build nests of their own and instead engage in sneaky egg drops that dupe other birds into fostering their young. The unwitting hosts are fooled into accepting and incubating the eggs, and raising the baby birds as their own. But not always: impostor eggs are sometimes rejected, turfed out or entombed under new layers of nesting material. 

For a long time, researchers have been conducting experiments to figure out what makes foreign eggs get turfed or treasured by placing artificial eggs in nests and then monitoring the reactions of the potential parents. These fake eggs would be made out of materials like plastic, wood or plaster, and the researchers would monitor the hosts' responses to receiving eggs of different sizes, colours and patterns. But such hand-produced eggs can be problematic: making them is time-consuming and prone to human error, and the end products aren't always uniform or convincing enough – all of which can make it hard for researchers to confirm their scientific findings.

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Image: A robin nest with four robin eggs and a beige 3D-printed cowbird egg. Image: Analia Lopez

So in what might be considered the most, er, egg-centric use for a 3D printer so far, Dr Mark Hauber, an expert in animal behaviour at Hunter College of the City University of New York, collaborated with nine other researchers to create the world’s first 3D-printed fake songbird eggs, testing them to see how realistic they were from a bird’s eye view. 

Hauber and his team printed faux brown-headed cowbird (Molothrus ater) eggs using a MakerBot 3D printer, and then painted them blue-green or beige. The eggs were then placed into the nests of free-living American robins (Turdus migratorius), a bird species that lays blue-green eggs and is occasionally an unwitting host of the cowbird, a North American brood parasite that lays beige spotted eggs. The results? The robins accepted all of the 3D-printed blue-green eggs as if they were their own, and rejected 79% of the beige cowbird-mimicking 3D eggs, a rejection rate similar to that seen in previous experiments with traditional plaster eggs.

These now bird-approved 3D-printed fakers are a welcome development. “[Birds] vary widely in how they respond to parasitic eggs, and this raises lots of cool questions about egg mimicry, the visual system of birds, the ability to count, cognitive rules about similarity, and the biomechanics of picking things up,” says Prof. Don Dearborn, chair of the Biology Department at Bates College, a brood parasitism expert who was not involved in the 3D-printing study. “For decades, tackling these questions has meant making your own fake eggs – something we all find to be slow, inexact and frustrating," he adds.

In this pilot study, the research team made eggs that were hollow, filling them with water to mimic the thermodynamic properties of real eggs. Hauber hopes that in future, 3D printers could produce eggs that mimic natural egg characteristics like colour, pattern, weight, shape, and texture, with thin eggshells that, like real ones, can be broken. “It’s really just the beginning,” he says.

This proof of concept for egg making is an innovative use for a 3D printer, and the team’s open-source plans for cowbird eggs may stimulate a new wave of experimental work.

Top header image: hjhipster, Flickr