Bird guides once listed the myrtle warbler and Audubon's warbler as distinct species that lived side by side in parts of their ranges. However, recent books show them as eastern and western forms of a single species, the yellow-rumped warbler. Apparently, the myrtle warbler and Audubon's warbler __________.
live in the same areas
are almost identical in appearance
are merging to form a single species
have undergone coevolution
successfully interbreed and produce fertile offspring