View Larger Pair of Masked Boobies, Sula dactylatra, ‘A by USFWS Pacific on Flickr.
This pair of masked boobies is considering nesting on Trig Island within the French Frigate Shoals (Kanemiloha’i), part of the Hawaiian Islands National Wildlife Refuge and the Papahanaumokuakea Marine National Monument. La Perouse Pinnacle can be seen in the background behind the birds. Detailed monitoring of masked booby reproductive success is conducted by US Fish & Wildlife staff and volunteers on adjacent Tern Island, and regular nest counts take place on the outer islands, including Trig Island. Although very similar, male and female birds can be distinguished by their size (females are usually larger), coloration (the bill and legs of males is usually more yellow), and voice (females emit a “honk”, while males produce a squeaky, whistle-like call).