Fortunately, conservationists are learning by trial and error how to successfully reintroduce Hawaiian crows into the wild, and they believe that all the challenges you read about can be overcome. First about the Hawks, actually, the unsuccessful reintroduction efforts have taught conservationists some useful lessons. They have realized that captive raised crows need to be trained to recognize and avoid Hawks. One way to train the crows is to play them recordings of Hawks' hunting calls together with crows warning cries. This way they learn that the Hawks calls represent danger. Another method is to show real live hawks to captive raised crows in an environment where the Hawks cannot harm the crows. This training seems to be working, because newly released crows can successfully protect themselves from a hawk attack. Second nest building Well, researchers have discovered why the males exhibited disruptive and aggressive behavior. You see, Hawaiian crows are highly social birds. They need to interact with other crows as they're developing in order to learn to behave in appropriate ways. Initially, captive males were raised in isolation apart from female crows, so the males did not have opportunities to develop necessary social skills. But once the conservationists realized this and started raising the males and females together, the males learned to interact with females much better and did not disrupt their nest building. Finally, egg hatching. While it's disappointing that the first clutch of eggs never hatched, it's actually not a major setback. What happened in the case you read about is that the crows laid infertile eggs. An egg is infertile if the birds did not mate successfully, when the female lays an egg, after an unsuccessful mating, the egg will fail to hatch. That pair of Hawaiian crows were actually first time parents, and it's very normal for first time parents to fail. Usually, first time parents have to try multiple times before they mate successfully and produce eggs that result in live chicks.