One other way birds can get "two summers". A few desert nesters in
Southern California cross the mountains to the coastal chapparal after
theri very early desert breeding season. Some examples are phainopeplas,
Costa's hummingbird, and occasionally Say's phoebe. For the
phainopeplas, I need to check, but I thought that those that failed an
earlier nesting in the desert would occasionally retry in the riparian
chaparral habitats.

Jim Neitzel
neitzelj at elwha.evergreen.edu