We woke in the first light of dawn this morning and went ashore on Isla San Esteban as the sunrise broke over the rugged hills and arroyos. Hiking up one of these dry valleys we encountered nesting yellow-footed gulls, beautiful cacti both new and familiar, and large lizards still cold and sluggish from the night. These were the endemic San Esteban giant chuckwalla (Sauromalus varius), a species found nowhere else on earth.
In the million years or so since San Esteban separated from the mainland, the chuckwallas here have evolved into a new species which is considerably larger than the ancestral species found on the mainland. The lack of predators and lower competition for food resources allowed the lizards which colonized the island to evolve a larger body mass, a common phenomenon among island species, termed "ecological release."
Our first stop in the Midriff islands was made very special indeed by seeing these unique creatures in their pristine desert habitat, all lit by the soft glow of the sunrise.
