For two months this spring, a pair of California condor parents carefully tended to a single, enormous egg. They took turns sitting on the egg to keep it warm, and they routinely rotated the egg, a behavior believed to promote proper chick development.

What the birds, part of a breeding population at the Oregon Zoo, did not appear to notice was that the egg was a high-tech fraud. The plastic shell, made with a 3-D printer, was stuffed with sensors designed to surreptitiously monitor conditions inside the condors’ nest.

For weeks, the dummy egg tracked the nest temperature, logged the birds’ egg-turning behaviors and recorded the ambient sound. The zoo hopes this data will allow it to better replicate natural conditions in the artificial incubators that are key to its condor breeding efforts.

California condors, which can have wingspans of nearly 10 feet, are critically endangered. So every year, when the birds lay their eggs, the zoo whisks them out of the nest and into the safety of the incubators. This strategy has several advantages, prompting some pairs to lay a second egg, enabling the zoo to monitor embryo development and protecting the fragile embryos from condor rowdiness.