Japanese weasels (Mustela itatsi) artificially introduced to Miyake-jima Island, a peripheral island of Japan, in the early 1980s increased predation on bird nests. We investigated the breeding biology of Japanese Bush Warblers (Horornis diphone) before and after the weasel introduction. Nest height was higher after than before the introduction, while clutch size did not differ significantly between the periods. These results suggest that introduced carnivores affect not only nest predation but also the nest site selection of birds.