Isla Rasa is a small but very special island in the Gulf of California, in the region known as the large islands. This island is flat, a characteristic from which it derives its name (rasa is “flat” in Spanish). It has a maximum height above sea level of only 33m and has several covered “valleys” of guano separated by “hills” formed by volcanic rock. This topographical configuration makes it ideal for nesting and it is a favorite spot for two species of seabirds –their concentration in this island is equivalent to 95% of these species’ entire population. The Heermann’s gull inhabits the entire Pacific coast from southern Canada and Guatemala, and migrates every year to nest on Isla Rasa. The elegant tern inhabits the coasts of Chile and Peru during its post-breeding season. Both species feed on small pelagic fish, mainly California pilchard (Sardinops caeruleus) and California anchovy (Engraulis mordax), while they remain on Isla Rasa. These fish species are also important for the fishing industry in the region and Mexico in general. The collapse of fish stocks is becoming more prevalent due to overexploitation.