“The eggshell fragments we found appeared abnormally thin,” Mr. Burnett said. “They were so thin that we had to run tests to confirm that it was a condor egg.” The fragments reminded him of the thin-shelled eggs from birds like brown pelicans and peregrine falcons, which had been devastated by DDT but are now on the rebound.
http://www.nytimes.com/2010/11/16/science/16condors.html?_r=1&src=twt&twt=nytenvironment