Masked booby

The Masked Booby: A Seabird of the Sulid Family

Imagine a bird that looks like it’s straight out of a tropical paradise, with its bright white plumage and black wings, and you might be picturing the masked booby. This large seabird is part of the sulid family, known for its typical body shape and striking appearance. But how much do we really know about this fascinating creature? Let’s dive into the world of the masked booby.

Taxonomy and Common Names

René-Primevère Lesson first described the masked booby in 1831, giving it the binomial name Sula dactylatra. The specific epithet ‘dactylatra’ refers to its splayed wingtips, while the genus name ‘Sula’ comes from Ancient Greek words meaning “blue face.” This bird has several alternative names, including masked gannet and blue-faced booby. It’s one of six species in the genus Sula, with a genetic study revealing that it shares close ties with the Nazca booby.

Geographic Distribution

The masked booby is found across tropical oceans except for the eastern Atlantic and Pacific, where it’s replaced by the Nazca booby. Its distribution spans from 30th parallel north to south, including the Indian Ocean, Pacific, Caribbean, and Atlantic Oceans. In the eastern Pacific off Colombia and Ecuador, you won’t find a masked booby; instead, you’ll encounter the Nazca booby.

Subspecies

The species has four recognized subspecies: S. d. dactylatra (Atlantic), S. d. melanops (western Indian Ocean), S. d. tasmani (Lord Howe Island), and S. d. fullagari (Tasman). M. O’Brien and J. Davies found the masked booby to be longer-winged, classifying it as S. d. fullagari.

Physical Characteristics

The masked booby is a large bird, measuring 75-85 cm in length with a wingspan of 160-170 cm and weighing between 1.2-2.2 kg. Its bare skin around the face, throat, and lores is described as black or blue-black. The plumage features a white mask-like appearance with brown-black feathers on the back, wings, and tail. The bill is pale yellow with a greenish tint, while the legs are yellow-orange or olive. The iris is yellow.

Juveniles

Young birds have a grey-brown head and upperparts, with a whitish neck collar. As they mature, white feathers appear on the head until it’s wholly white by 14 to 15 months of age.

Behavior and Ecology

The masked booby’s call consists of a descending whistle for males and a loud honk for females. It can be distinguished from related species such as the Nazca booby by its yellow bill and larger size. The bird nests on steep cliffs, while the red-footed booby has a white morph similar to the masked booby but is smaller.

Nesting Colonies

The largest breeding colony of masked boobies can be found on Clipperton Island in the eastern Pacific Ocean with 112,000 birds. Breeding takes place at different times of year throughout its range, with varying peak egg-laying periods on different islands.

Migration and Foraging

The masked booby generally flies 7m high, and at speeds of up to 70km/h, alternating between gliding and active flying with strong wingbeats. It is often encountered alone or in a small group when returning to its colony.

Long-Distance Travel

A bird tagged at Nepean Island was recovered after being caught in fishing gear 24 years and 9.9 months later, traveling 713 km away off the Isle of Pines in New Caledonia. The longest distance traveled by a masked booby is 3,152 km.

Reproduction

The masked booby begins breeding around four or five years of age, forming monogamous relationships with many pairs remaining together over multiple breeding seasons. Adults are highly territorial when nesting, engaging in agonistic displays to mark their territory and defend against neighbors and intruders.

Incubation and Chicks

The nest is a cleared area with a shallow depression containing two chalky white eggs. The eggs are incubated by both adults for 45 days, with parents using their webbed feet to rest on the ground. After hatching, chicks are altricial and nidicolous, covering less than 10 cm long, weighing around 40-60 g at birth. They develop feathers over several weeks and fledge at around 120 days of age.

Diet and Foraging

Masked boobies dive from heights of 12-100 m above the water, reaching depths of up to 3 m in search of fish. They swallow their catch underwater. Fieldwork at Clipperton Island showed that masked boobies flew an average of 103 km (64 mi) to forage, with a maximum range of 242 km (150 mi), and did not rest at sea at night.

Threats and Conservation

Predators include silver gulls, buff-banded rails, feral cats, ticks, green sea turtles, and rats. The International Union for Conservation of Nature lists the masked booby as a species of least concern, but its population is decreasing due to climate change posing a threat to breeding success because of reduced food supply and rising sea levels.

While the masked booby faces few threats overall, it’s important to monitor its populations closely. After all, every bird counts in our interconnected ecosystem. The next time you hear about seabirds, remember the masked booby – a true marvel of nature’s diversity.