National Geographic : 1988 Jan
S EABIRD'S-EYE VIEW of Genovesa Island (below) takes in mile-wide Darwin Bay, a volcanic caldera eroded by the sea; inland, a smaller crater awaits the sculpting waves. On the bay a pretty coral beach is a popular stop for cruise-ship visitors, especially during the first six months of the year when frigatebirds put on madcap courtship displays in their colony. Males perch amid intended nesting sites in shrubs and inflate stoplight red gular sacs to catch the eyes of females cruising overhead. When a potential mate is in sight, the male raises and quivers his wings, shakes head and pouch, and wails for all he is worth. With his heart in his throat, one suitor wins (left). The pair then builds a hap hazard nest, often filching twigs from the nests of neighboring red-footed boobies or from other frigatebirds. The female lays a single egg, incubated for seven to eight weeks by both parents. Deprived of food during week long shifts, each may lose 20 percent of its weight. After hatching, the chick must ini tially be guarded by one adult against marauding frigatebirds or short-eared owls, while the other parent forages at sea. This dependency lasts five long months, until the fledgling takes wing, and helps explain why frigatebirds practice air piracy. They often waylay inbound boo bies and harass them until they drop their catch in mid-flight, and the food goes instead into the bottomless pit of the frigatebird chick. The adults' hunting is limited to catching sea-surface prey from the air they do not dive. But the frigatebird's maneuverability is incredible, and no booby with a full dinner pail stands a chance.