Masked Booby, Sula dactylatra
Masked Booby, Sula dactylatra personata. Photograph taken in coastal waters off BahÃa Solano, Columbia, May 2022. Photograph and identification courtesy of Chris Wheaton, Fullerton, California.
Background and Identification
The Masked Booby, Sula dactylatra personata, is one of four subspecies of Masked Booby, of which two are found in Mexico. They are a member of the Sulidae Family of Boobies and Gannets, that has ten members placed in three genera, and one of six global species in the Sula Genus. They are also known as the Blue-faced Booby and the White-faced Booby and in Mexico as bobo enmascarado.
The Masked Booby is the largest of the boobies that is found in small to medium-sized colonies. The sexes are similar in appearance, but the females are larger than the males. They are a bright white color with black primaries, secondaries, humerals and tails. The wings have white margins, less and median coverts and some outer primary-coverts. Their underwing coverts are white, and their remiges are black distally and broadly tined in silvery-gray at the base. Their bills have a thick base and tapers to the tip without much curvature and are yellow in color with some having an orange tip, their iris is yellow or orange-yellow, and their legs and feet vary from lead grayish or bluish, to dull orange or yellow, to olive or khaki. The black skin around the eye extends narrowly to the upper bill base and on lores to upper throat and is lighter on the chin and lores.
Habitat and Geographical Range
The Masked Booby forages exclusively in the blue-water pelagic zone thought tropical oceans as a high velocity plunge diver that feed exclusively on fish (predominantly flying fish) and squid often hundreds of miles from nearest land. They are known to travel up to 2,000 km and have been seen feeding greater than 1,000 km from nearest land. They associate with dolphin and tuna schools in the Pacific depending on the dolphin and tuna to drive prey fish to the sea surface. Feeding flocks can range in size from one to several hundred birds. They roost and breed exclusively on hundreds of small oceanic islands that are flat and unforested within 30o of the equator. They favor locations near cliff edges or high spots that facilitate taking flight. They are colonial nesters with each female laying one or two eggs. One chick is raised and the other believed to be killed by silicide.
The Masked Booby has a very limited range in Mexico being found in close proximity to the oceanic islands of the Caribbean along the East Coast of the Yucatan Peninsula and the oceanic islands in the Pacific off Western Mexico. The personata subspecies is found in islands off Western Mexico including Alijos Rocks, Clarion Island, Clipperton Island and San Benedicto Island.
Common Misidentifications
The Masked Booby is very similar to and very difficult to distinguish from the Nazca Booby, Sula granti. Until 2000 the Nazca Booby was considered to be a sub-species of Masked Booby when it was recognized as a full species by the American Ornithologist’s Union. In 2002 this was reconfirmed by molecular variation at the cytochrome-b gene. Complicating the discussion is that the two species mate assortatively where sympatric. Morphologically the Masked Booby is larger in stature and has a longer thicker yellow bill than the Nazca Booby (orange or pink bill). The Masked Booby is also similar to the White Morph of the Red-footed Booby, Sula sula (bluish smaller bill).
Conservation Status
From a conservation perspective the Masked Booby is currently considered to be of Least Concern with stable, or slightly declining, widely distributed populations. Their long-term viability is exceptionally vulnerable to human development of isolated oceanic islands and the introduction of predators. They are hunted by humans for eggs and meat. Their populations are prone to predation by feral cats, feral pigs, and rats. Their breeding habitat has been lost in some areas via the planting of coconuts and housing developments.