Conclusions
In the West, the migratory population of monarch butterflies is collapsing. Based on available information, a new resident population seems to be expanding in urban gardens. Our assessment is that the resident population is much smaller and is unlikely to replace the migratory one. One could assume that the resident population is a conservation success or, alternatively, a cause of the decline of monarch migration in the West. In fact, we do not know if either of these is true. This startling transition emphasizes the general need to be prepared to rapidly reorient conservation policies and practices in changing environments.