3D-Printed Eggs Show How Birds Reject Nest Imposters [VIDEO]

"Fool me once, shame on you. Fool me twice, shame on me." This common adage applies to a new study in which scientists used 3D-printed eggs to show how wild birds reject nest imposters.

For decades, researchers have been making artificial eggs out of plaster, wood and other materials to better understand bird behavior when it comes to invading "brooding parasites." These birds don't build nests of their own, but rather sneak their own eggs into other nests. This way, these cunning birds trick their peers into raising invading chicks, sometimes even at the expense of their own.

In some species, this has caused birds to develop ways of identifying imposters and rejecting eggs that aren't theirs, using cues such as egg size, shape, color and pattern. Meanwhile, brooding parasites have gotten better and better at disguising their eggs to mimic those of host species.

So to better understand how wild birds get around this problem, a team of scientists created digital models of the eggs of Brown-headed Cowbirds (a North American brood parasite) using 3D printing. This method also allowed them to create hollow eggs that could then be filled with either water or gel, closely mimicking not just the weight but even the thermodynamic properties of real eggs (You can watch a video of an egg being printed here).

The researchers painted the eggs to match either the beige of real cowbird eggs or the blue-green of host American robins. The 3D-printed eggs were then placed in robin nests that were monitored for six days to see how the parents reacted.

What they found was that the robins accepted 100 percent of the blue-green eggs but rejected 79 percent of the eggs painted to resemble those of cowbirds. This is similar to past studies that used traditionally produced plaster eggs. However, this time 3D-printed eggs have the advantage of being less variable and more able to reproduce a desired size and shape.

"Hosts of brood parasites 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," Don Dearborn, a brood parasitism expert who was not involved in the study, said in a press release. "For decades, tackling these questions has meant making your own fake eggs-something we all find to be slow, inexact and frustrating. This study uses 3D printing for a more nuanced and repeatable egg-making process, which in turn will allow more refined experiments on host-parasite coevolution."

The results were published in the journal PeerJ.

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