Just because an egg is a dummy doesn’t mean it has to act like one. Last month the International Centre for Birds of Prey (ICBP) in England started planting decoy eggs in the nests of captive-bred vultures to act as oval spies, collecting stats on how vultures incubate their embryos so that conservationists can improve their own hatching techniques. The 3-D-printed gadgets, known as EggDuino, are part of a larger push to keep vultures around the world from becoming obsolete. Each faux egg costs about $250 to make. (So far, the electronics company that's producing them, MicroDuino, has fronted the cost of everything but the shell.) A seam around the middle unscrews to reveal tiny Arduino sensors—similar to the hardware inside smartphones—that measure nest factors such as temperature, humidity, and barometric pressure. The sensors also track the egg’s movements as the parents turn it (to prevent the developing embryos from sticking). Experts at ICBP plan to use...