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.