Endemics can easily become endangered or extinct because of only living in a small area. They are also vulnerable to the actions of man, including the introduction of new organisms. There were millions of both Bermuda petrels and "Bermuda cedars" (actually junipers) in Bermuda when it was settled at the start of the 17th century. By the end of the century, the petrels were thought to be extinct. Cedars, whose numbers were low as a result of centuries of shipbuilding, were nearly made extinct in the 20th Century by the introduction of a parasite. Both petrels and cedars are very rare today, as are other species endemic or native to Bermuda.