Boobies vs. Gannets: How to Identify These Fascinating Seabirds

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Boobies vs. Gannets: How to Identify These Fascinating Seabirds

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Boobies vs. Gannets: How to Identify These Fascinating Seabirds

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Paul Vergara
April 20, 2011

Boobies and gannets are fascinating members of the family Sulidae and the order Suliformes, comprising ten species of large tropical seabirds. Ranging from 60 to 85 cm (24 to 33 inches) in length, they boast impressive wingspans of about 140 to 175 cm (4.59 to 5.74 feet). These seabirds can be found in all oceanic regions except for Antarctica, with gannets thriving in tropical and subtropical waters, while boobies prefer temperate environments. Below is a breakdown of the various species of boobies and gannets along with their geographical distributions:

Gannets

  • Northern gannet (Morus bassanus) - Found in Western Europe and North America.
  • Cape gannet (Morus capensis) - Located along the West to Southwest African coast.
  • Australasian gannet (Morus serrator) - Native to Australia and New Zealand.

Boobies

  • Abbott's booby (Papasula abbotti) - Found on Assumption Island.
  • Blue-footed booby (Sula nebouxii) - Inhabits the Eastern Pacific from California to the Galapagos and Peru.
  • Masked booby (Sula dactylatra) - Roams tropical oceans, including the Indian Ocean, from the coastlines of the Arabian Peninsula and East Africa to Sumatra and Western Australia.
  • Nazca booby (Sula granti) - Distributed across the Eastern Pacific, from Baja California to the Galapagos, Isla de la Plata in Ecuador, and Malpelo in Colombia.
  • Brown booby (Sula leucogaster) - Resides in tropical areas of the Atlantic and Pacific Oceans.
  • Red-footed booby (Sula sula) - Found on Christmas and Galapagos Islands.
  • Peruvian booby (Sula variegata) - Lives along the coasts of Ecuador, Peru, and Chile.
Abbott's booby is an endangered seabird, smaller than gannets, and classified in its own monotypic genus. It was first identified from a specimen collected by William Louis Abbott on Assumption Island in 1892
The Australasian or Australian gannet. Adults are mostly white, with black flight feathers at the wingtips and lining the trailing edge of the wing. The central tail feathers are also black. The head is tinged buff-yellow, with a pale blue-grey bill edged in black, and blue-rimmed eyes.

Similarities and differences

While some sulids are pelagic, others prefer inshore marine environments. Breeding sites typically include offshore islands and continental coastlines. The eggs of these birds are incubated for 42 to 55 days, and the chicks are altricial, remaining in the nest for about 14 to 22 weeks. Post-fledging care can last from five to nine months, with adult plumage and sexual maturity occurring between two to six years. Their flight feathers are molted almost continuously, and these seabirds can live for 10 to 20 years or more.

The Cape Gannet (Morus capensis) is listed as Vulnerable, facing main threats such as habitat destruction, human collection of eggs, chicks, and adults, and overfishing by commercial industries.

With the exception of the red-footed booby, boobies exhibit sexual size dimorphism, meaning females are larger and heavier than males. In contrast, gannets appear monomorphic in size. Most species have a white ventral plumage, complemented by brown or black on their primaries, dorsal feathers, or heads. Juveniles are generally darker than adults. Their wings are long and set far back on their bodies, while their stout, conical bills often have serrated edges in certain species.

Female and male blue-footed boobies exhibit sexual dimorphism; the female is slightly larger and her pupil appears more dilated than that of the male

Both gannets and boobies possess nostrils that are not externally visible, featuring nasal grooves along their bills. Adults have bare facial and gular skin, which can be black, red, or blue, along with colorful feet. Their eyes, located beside the bill, provide binocular vision, with irises often pale in color. Notably, sulids lack brood patches. Their legs are short and positioned far back on their bodies, and their feet are totipalmate (webbed between all four toes), with the middle toenail being pectinate.

The masked and Nazca boobies: notice the distinction between the yellow-billed Masked Booby and the orange-billed Nazca Booby.

Gannets

Gannets inhabit the colder waters of the northern Atlantic and temperate regions around Africa, Australia, and New Zealand. Adult gannets are predominantly white, with distinctive black-tipped wing feathers. Their large, yellowish or buff-colored heads are marked with black around the eyes. They have tapered beaks and pointed tails, making them adept hunters. Gannets dive into the sea with half-closed wings to catch fish and squid.

The largest of the three species is the northern gannet, measuring 100 cm (40 inches) and sometimes referred to as the solan goose. It breeds on islands in Canada, Greenland, Iceland, and northeastern Europe, wintering in the Gulf of Mexico, Morocco, and the Mediterranean.

On land, gannets waddle, but they are expert fliers, skillfully alternating rapid wing beats with gliding. They spend most of their lives over the water and nest in dense colonies on cliffs. A female gannet broods a single bluish, chalky egg for six to seven weeks in a nest made of seaweed or mud. The young are fed through regurgitation and reach maturity in their third or fourth year.

Boobies

Boobies also nest in colonies but possess a highly developed sense of territory. Their courtship rituals include elaborate displays, where the male performs a dance, raising his feet alternately several times. This is followed by a behavior known as sky-pointing: the birds extend their wings horizontally towards the tail and raise their heads, while males emit long, continuous whistles and females honk repeatedly.

The brown booby is the most common and widespread species. Gregarious by nature, it forages at low heights over inshore waters. Unlike other species, it nests exclusively on the ground and prefers to roost on solid objects rather than on the water's surface.
The Peruvian booby is an endemic bird of the Peruvian ocean current, with a distribution that is much more limited than that of other closely related species. It plays a vital role as a guano-producing seabird.
The red-footed booby nests exclusively in shrubs or trees, laying a single egg. This pelagic bird is not sexually dimorphic, as males and females share similar appearances and both produce a distinctive squawking call

Boobies typically lay one to three eggs directly on the ground or in trees (as seen with the red-footed booby). These charming birds earned their name from their tameness and lack of fear of humans, making them a delightful sight for birdwatchers and nature lovers alike.

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