Sula dactylatramasked booby

Geographic Range

Masked boobies are fairly widespread; they are found primarily in the Atlantic and Pacific oceans. In the United States they are restricted to the three Hawaiian islands of Lehau, Moku Manu and Kaula. They are found mainly in the tropics. Masked boobies are found off the Yucatan peninsula and in much of South America. There are a variety of boobies with different ranges, but masked boobies are found on many islands between 30 degrees N and 30 degrees S, with tiny habitats from the Pacific to the Red Sea, and even on islands near Indonesia and Australia. (Anderson, 1993)


Boobies prefer to live on small, flat islands without trees. They often nest on the edges of cliffs or in flat areas that allow for easy take-off. They spend much of their time foraging over the ocean far from land. (Anderson, 1993)

Physical Description

Masked boobies are graceful birds, their body is white, they have black on thier wings and tails and a black mask around their beak and eyes. They are the biggest species of boobies. Females are larger than males, ranging from 75 to 86 cm long, males are from 74 to 82 cm long. They weigh from 1220 to 2353 g and have wingspans of 152 cm, on average. It is difficult to tell males and females apart because they both have bright white plumage as adults; young boobies are often mistaken for northern gannets (Morus bassanus). Masked boobies are born naked but are completely covered with feathers after 35 to 40 days. Juveniles are grey with white underparts and do not look like adults until their fourth year. (Anderson, 1993; National Wildlife Refuge, 2000)

  • Sexual Dimorphism
  • sexes alike
  • female larger
  • Range mass
    1220 to 2353 g
    43.00 to 82.93 oz
  • Range length
    74 to 86 cm
    29.13 to 33.86 in
  • Average wingspan
    152 cm
    59.84 in
  • Average basal metabolic rate
    5.5209 W


Boobies have intricate mating rituals; males attract females by stretching out their necks and presenting gifts such as small stones and feathers to their perspective mates. After a slow walk they copulate; copulation takes ten to twenty seconds, and the female begins incubating immediately after laying the first egg. (Anderson, 1993)

Breeding seasons vary widely throughout the range of masked boobies; they can occur from February to August, January to July, and August to March. Masked boobies nest colonially; their nests are small hollows in the ground. The female usually lays two eggs. Incubation lasts 43 days on average. Masked boobies do not have brood patches, so they incubate the eggs with their feet. The first chick to hatch kicks the second chick out of the nest, so parents raise only one offspring. The chick fledges in 109 to 151 days and is intependent in one to two months. Juveniles reach sexual maturity in 3 to 5 years. (Anderson, 1993; National Wildlife Refuge, 2000)

  • Breeding season
    Breeding seaons vary widely throughout the range of masked boobies.
  • Range eggs per season
    1 to 2
  • Average eggs per season
  • Average eggs per season
  • Average time to hatching
    43 days
  • Range fledging age
    109 to 151 days
  • Range time to independence
    1 to 2 months
  • Range age at sexual or reproductive maturity (female)
    3 to 5 years
  • Range age at sexual or reproductive maturity (male)
    3 to 5 years

Both males and femles incubate the eggs. The first chick to hatch kicks the second chick out of the nest, so the parents only raise one offspring. Chicks are usually fed only once or twice a day. Both parents feed their young, but females may bring more food to the nest than males. Both parents continue to protect and feed their chick for one to two months after it fledges. (Kepler, 1969; National Wildlife Refuge, 2000)

  • Parental Investment
  • no parental involvement
  • altricial
  • pre-hatching/birth
    • protecting
      • male
      • female
  • pre-weaning/fledging
    • provisioning
      • male
      • female
    • protecting
      • male
      • female
  • pre-independence
    • provisioning
      • male
      • female
    • protecting
      • male
      • female


Masked Boobies have a lifespan of 15 to 20 years; the longest known lifespan is 20 years. (Anderson, 1993; Kepler, 1969; National Wildlife Refuge, 2000)


Masked boobies usually nest colonially. They are quick to sound an alarm if suprised or threatened but are not aggressive and are sometimes friendly to humans. Masked boobies spend most of their time out at sea in search of food. They usually feed diurnally. (Anderson, 1993)

Home Range

We do not have information on home range for this species at this time.

Communication and Perception

Males have a high-pitched whistle while females have a more "honky" sounding call. Males will communicate by calling during their courtship displays or when they are frightened or alarmed. Females only call for help and as a warning. Both sexes are usually silent at night. (Anderson, 1993)

Food Habits

Boobies have a diet consisting mostly of fish and squid. They catch their prey by diving from heights of up to 30 m. When collecting food for offspring, boobies usually tend to stay closer to land, otherwise they hunt around 65 km from shore. (Anderson, 1993; National Wildlife Refuge, 2000)

  • Animal Foods
  • fish
  • mollusks


There are no known predators of masked boobies. Because they are not usually found in dense populations and because they nest on islands, it might be hard for predators to rely on them as prey. (Great Barrier Reef - Reef Education, 1996)

Ecosystem Roles

Because masked boobies do not occur in dense populations, they do not seriously affect fish populations where they feed, nor are they important food sources for predators. (Anderson, 1993)

Economic Importance for Humans: Positive

Fishermen sometimes find schools of tuna by following feeding boobies; without knowing it, boobies provide fisherman with information on the best places to find fish. Boobies are also popular among birdwatchers. (Anderson, 1993)

Economic Importance for Humans: Negative

There are no known adverse affects of masked boobies on humans.

Conservation Status

Interactions with humans seem to have had little effect on the species. Thousands of tourists pass close by their nests in the Galapagos, seemingly without any negative effects. Though there have been a few cases of boobies caught in fishing traps, these numbers are reportedly small. (Anderson, 1993)


Alaine Camfield (editor), Animal Diversity Web.

Paul Mansoor (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, University of Michigan-Ann Arbor.



Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

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living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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living in the southern part of the New World. In other words, Central and South America.

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uses sound to communicate


young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


an animal that mainly eats meat


uses smells or other chemicals to communicate


the nearshore aquatic habitats near a coast, or shoreline.


used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

  1. active during the day, 2. lasting for one day.

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.


animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).


eats mollusks, members of Phylum Mollusca


Having one mate at a time.


having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.


generally wanders from place to place, usually within a well-defined range.

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.


found in the oriental region of the world. In other words, India and southeast Asia.

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reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.


An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).


an animal that mainly eats fish

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.


reproduction that includes combining the genetic contribution of two individuals, a male and a female


associates with others of its species; forms social groups.


uses touch to communicate


Living on the ground.


the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.


uses sight to communicate

year-round breeding

breeding takes place throughout the year


Anderson, D. 1993. Sula dactylatra - Masked Booby. The Birds of North America, No. 73, 1993: 1-16.

Great Barrier Reef - Reef Education, 1996. "GBR Explorer - Boobies" (On-line). Boobies. Accessed April 20, 2004 at

Kepler, C. 1969. Breeding Biology of the Blue-Faced Booby on Green Island, Kure Atoll. Cambridge, MA: Nuttall Ornithological Club.

National Wildlife Refuge, 2000. "Masked Booby" (On-line). Accessed April 20, 2004 at