Sula leucogaster

Geographic Range

Brown boobies, Sula leucogaster , are common residents of Puerto Rico and the Virgin Islands. The distribution is described as pantropical, between latitudes 30 degrees North and 30 degrees South, though it extends to about 34 degrees South in the central Pacific. Brown boobies occur in the Caribbean Sea, Red Sea, and the Atlantic, Pacific, and Indian Oceans. They also inhabit seas north of Australia. The subspecies Sula leucogaster brewslei and Sula leucogaster etesiaca live along the Pacific coast of Mexico and the Pacific coast of Central and South America, respectively.

Although brown boobies may have historically inhabited the Florida Keys, clear evidence is lacking. Tropical storms occasionally blow individuals of this species well outside of their typical geographic boundaries - such an example is the October 2008 observation of a lone Sula leucogaster at Claytor Lake (Pulaski County) in southwestern (interior) Virginia.

• Biogeographic Regions
• neotropical neotropical
  • native native
• australian australian
  • native native
• oceanic islands oceanic islands
  • native native
• indian ocean
  • native native
• atlantic ocean atlantic ocean
  • native native
• pacific ocean pacific ocean
  • native native

Habitat

Brown boobies use coral atolls and volcanic stack islands for nesting in tropical or subtropical waters. When faced with little or no competition for space, they prefer wide open spaces at sea level. They have, however, been found on cliffs and hillsides.

• Habitat Regions
• tropical tropical
• saltwater or marine saltwater or marine

• Aquatic Biomes
• coastal coastal

Physical Description

Adult feather coloration is similar between sexes. There are small differences among males of the subspecies S. leucogaster brewslei and S. leucogaster etesiaca . Generally brown boobies have dark brown heads, necks, and backs with bright white underbellies. A sharp line separates the lower breast where the brown fades to white. The under wings are mostly white except for a variable dark bar that is relatively narrow and extends from armpit to carpal joints. The subspecies mentioned earlier tend to have a light gray to white head that gradually turns brown at the neck. Overall their necks and upper backs are darker than other Sula leucogaster subspecies. Juveniles have no documented differences between sexes or subspecies. But are generally a brownish color on their head, neck, and back with a noticeable band across the lower breast which leads to the mottled brown and whitish underparts (underparts gradually attain full white color over first 2 years). The under wing-coverts (feathers that cover the bases of the quill feathers) are generally gray, which contrast significantly with the rest of the under wing. Adult soft part colors vary slightly between males and females, with no documented variation among subspecies. Males have gray-blue to steely-blue skin around the eyes and yellow to bright yellow skin at base of mandible. Females are much the same, except for face skin that is always bright yellow. In both genders the bills and feet range in color from bright yellow, bluish yellow, greenish yellow, light-pink, and gray.

Overall distinguishing booby species isn’t difficult, but juvenile red-footed boobies ( Sula sula ) look remarkably similar to juvenile brown boobies. Overall length ranges from 64 to 85 cm, with females on average being a few cm longer. Their wingspan is in the range of 132 to 155 cm. There is a slight difference in weight between sexes, with females usually weighing about 300 g heavier. The ranges for males are 950 to 1700 g and for females is 1000 to 1800 g.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger
• sexes colored or patterned differently

Reproduction

Brown boobies are monogamous. Males are the only gender observed performing mating behaviors, including sky-pointing and parading. In sky-pointing, when a female first approaches, the male will stand up and throw his head into the air with neck stretched out as far as it can go. This is usually accompanied by a unique whistle. This ritual is slightly different from the other booby species, as it doesn’t involve a use of the wings. Parading is just an exaggerated form of walking, in which body posture is unusually erect with an exaggerated sway. Other behaviors that are thought to reinforce pair bonding are mutual preening, bill touching, and bowing. Mutual preening is where each pair bond will clean the other’s feathers. Bill touching is done whenever mates return to their own territory after bowing. It has been noted that the mate reentering the territory will make their arrival call and then perform a slight bow (similar to the bow described in aggressive behavior) unless the bird reentering is flying in and its partner is on a nest, in which case that bird will perform a seated bow. This is thought to be a form of greeting.

• Mating System
• monogamous monogamous

Brown booby breeding season is dependent upon food availability. Events such as El Nino can drastically shift normal breeding season for a few years. In the Caribbean and east Pacific, peak breeding months are December to February. In the central Pacific, the breeding season lasts from December to March, but it's not uncommon to find them breeding year round. In Hawaii brown boobies breed from March to May. After eggs are laid, parents take turns incubating for 42 days. Usually brown boobies lay 2 eggs but only raise one chick past the fledgling stage. It is thought that having a second egg is for insurance purposes, in case one egg doesn't make it. The first chick hatches about 2 to 4 days before the second. This chick will then push the other young from the nest with no interference from either parent. The expelled chick will usually die from heat exposure, lack of food, or predation. The surviving chick will continue to be cared for in the pre-fledgling stage for close to 100 days, during which time both parents continue to feed and protect it. In the post-fledgling stage, it is not uncommon for young birds to go out on their own to learn how to hunt and socialize and then return to their parents nest to be fed. This sort of behavior has been observed up to a year after reaching post-fledgling stage, but it typically lasts 50 days. This variability is thought to be the result of food availability.

• Key Reproductive Features
• iteroparous iteroparous
• year-round breeding year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • external external
• oviparous oviparous

Both male and female brown boobies incubate the eggs. Time on the nest is split evenly, with varying amount of hours per sitting. Once eggs hatch, both parents participate in feeding the young. There are no records about which gender feeds more often. When chick gets older and bigger the parents might roost away from nest but will often return to defend their nest territory and chick. This pre-fledgling care can continue up to 100 days. Post-fledgling care can vary from 42 days up to 259 days with rare occurrences of juveniles returning to parents nest up to a year after to beg for food. This factor is thought to be controlled by local fishing conditions. If food is plentiful and easy for juveniles to catch and learn how to hunt efficiently, then it will be shorter. There have been no documented cases of adult brown boobies showing post-fledgling chicks how to dive or hunt. However, in an experiment by Yoda et al. (2007), hand-raised chicks were often much slower to reach peak diving levels than chicks raised by parents.

• Parental Investment
• altricial altricial
• male parental care male parental care
• female parental care female parental care
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • male
    • female
• pre-weaning/fledging
  • provisioning
    • male
    • female
  • protecting
    • male
    • female
• pre-independence
  • provisioning
    • male
    • female
  • protecting
    • male
    • female
• extended period of juvenile learning

Lifespan/Longevity

Adult mortality per year has been reported to be between 3.3 and 7.7%. The maximum known lifespan in the wild is 27.2 years. There have been no studies to document average lifespans in the wild or captivity.

Behavior

There hasn't been enough studies outside of the breeding season to determine whether brown boobies migrate. They do disperse from nesting areas at the end of the breeding season and return 1 to 3 weeks before laying occurs, but they may simply disperse to local waters for foraging. Brown boobies moves around while on land with a waddling gait (similar to a duck) and only hop when an intruder comes into its territory. They have never been recorded climbing. Brown booby flight in groups is not patterned. They fly alone and in flocks to foraging areas. Brown boobies are estimated to fly at speeds up to 40 km/h and can glide efficiently. Because of their smaller size, males tend to be more agile than females and both species are capable of landing on tree limbs, buoys, and vessels at sea. When on land during day, brown boobies spends a good deal of time preening and reapplying water proofing oil secreted from the uropygeal gland. Brown boobies are capable of sleeping while standing or sitting. Generally, the bill is tucked over the back and into scapulars or with the neck drawn in and beak facing forward.

• Key Behaviors
• terricolous
• flies
• glides
• diurnal diurnal
• motile motile
• sedentary sedentary
• territorial territorial
• social social
• colonial colonial

Home Range

Brown boobies typically defend an area of about 1 to 5 meters around nests. Size varies based on nest substrate and the density of other brown boobies in the colony. No studies have been done on defending feeding areas.

Communication and Perception

There has only been one study on the various calls of brown boobies. The results of that study suggest vocalizations are used for several different functions, including greeting mates, aggression, and chicks begging for food. Colonies as a whole are generally not noisy, as more communication is done through behavior. Males and females use vocalizations in different ways. Males emit a series of soft whistles while females are responsible for harsh quacking or honking. These sounds become more pronounced whenever they are faced with possible intrusion from another bird. Males calls become harsher and are held for longer while females emit a sound known as a “roar-call”. This is an emphatic shout that is intended to warn the intruder to stay away from the nest. When these birds greet their mates as they return from hunting, they use their typical sounds. However, these calls are made softly while still far out and tend to get louder as they approach the nest.

Hatchlings have their own range of sounds, starting with peeping while still in the egg. While very young there seems to be no discernible pattern to the food call, it is just a range of the noises they are able to make. As they get older it takes on a loud, raspy, repetitive craa-craaaa.

Most communication is accomplished through behaviors rather than sounds. An example of aggressive behavior will be seen mostly when claiming or maintaining breed sites. Aggressive behaviors are directed towards other birds as well as inanimate objects (shrubs or rocks). When performing aggressive behaviors against other birds, brown boobies hop towards the intruder with their neck and head stretched forward. When they get closer they bow and usually emit a honk. If the intruder does not back down the defending booby will perform a more exaggerated bow. If the intruder still doesn’t back down, then the territory owner may rattle its bill towards the intruder. This can escalate to bill jabbing with a downward slap of the wings. Sometimes the defender will grab onto others bill or neck.

Only males have been observed performing mating behaviors, which include sky-pointing and parading. Sky-pointing is done when a female first approaches. The male will stand up and throw his head into the air with neck stretched out as far as it can go. This is usually accompanied by a unique whistle. This ritual is slightly different from the other booby species as it doesn’t involve a use of the wings. Parading is really just an exaggerated form of walking. The body posture is unusually erect with an exaggerated sway. Other behaviors that are thought to reinforce pair bonding are mutual preening, bill touching, and bowing. Mutual preening is where each pair bond will clean the other’s feathers. Bill touching is done whenever mates return to their own territory after bowing. It has been noted that the mate reentering the territory will make their arrival call and then perform a slight bow (similar to bow described in aggressive behavior) unless the bird reentering is flying in and its partner is on a nest. In which case that bird will perform a seated bow. This action is thought to be a form of greeting.

• Communication Channels
• visual visual
• tactile tactile
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Brown boobies eat mainly fish. They consume most species of fish that are from 5 to 40 cm in length. Observed prey include flying fish ( Exocoetus species), goat fish ( Mullidae ), squirrelfish ( Holocentrus diadema ), mackerel ( Rastrelliger kanagurta ), and ommastrephid squid ( Ommastrephidae ).

To acquire food, brown boobies use mainly plunge-diving. This is where they rise to 10 to 12 m above the water to search for prey before angling the body in such a way that it can enter the water as smoothly as possible. This position changes throughout the dive, starting with the initial descent. At the time of the descent the wings are folded in tightly next to the body, then thrust straight out over their back (prior to entering water) until their wings are touching over the center of their back. Depending on their altitude prior to diving, they are able to submerge themselves up to 2 m deep. They have also been known to pursue prey underwater using a combination of feet and wing motions.

Along with plunge-diving, some fledglings (about 1 in 100) and some adults (1 in 500) practice kleptoparasitism, where they steal prey from other seabirds. For example, brown boobies have been observed stealing prey from great frigatebirds ( Fregata minor ) as they transfer food to their young. It is thought that fledgling frigatebird calls for food are what attracts boobies.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore
  • molluscivore molluscivore

• Animal Foods
• fish
• mollusks

Predation

Sally lightfoot crabs ( Grapsus grapsus ) are the only known predators of brown booby hatchlings. While these crabs mostly forage around nesting sites picking up feathers, egg shells, dead chicks, and dry bird excrement, they will on very rare occasions prey on recently hatched chicks that have been expelled from the nest. In these cases, adult birds do nothing to protect their young from the crabs and the crabs have never been seen going into the nests after a solitary chick. Brown booby young may also be preyed on by larger seabirds and nesting colonies may be threatened by introduced predators, such as rats, cats, and pigs.

Ecosystem Roles

Richardson (2006) report that the presence of seabird nesting colonies (including Sula leucogaster on islands increases the productivity of certain trees (like mangroves) more than islands without nesting colonies. Recently, this species, Sula leucogaster , has been found to be one of the many contributing factors (along with all other nesting seabird colonies) to eutrophication of the surrounding waters of the islands they inhabit. Their nutrient-rich feces causes lower species diversity and greater dominance of mostly epiphytic biota but also macro-algae and phytoplankton. The rapid growth of the epiphytes blanket the sea grass beds and eventually causes them to die from lack of sunlight. Any organism in the area that depended on the sea grass that is unable to accommodate the change will soon die after it. However, no studies have examined direct effects of eutrophication on the nesting sea birds from presumed declines in fish in the surrounding water.

Brown boobies are also host to the parasite Babesia poelea . Work and Rameyer's (1997) research pointed to the possibility that avian piroplasms may be species specific and be transmitted by argasid ticks ( Ornithodoros capensis ).

• Ecosystem Impact
• biodegradation biodegradation
• parasite parasite

Economic Importance for Humans: Positive

According to Spennemann (1999), at the turn of the 20th century brown booby feathers were in high demand from the European and American fashion industry. These feathers were used to adorn women's hats and the "take" of such feathers led to 2 million bird deaths (not all Sula leucogaster ). This demand has since died down and regulations are in place to prevent over-harvesting for the fashion industry or any other products. Several countries (e.g., Japan and Madagascar) are turning to ecotourism as a source of income and have set aside several islands with very strict regulations to preserve the natural environment. Ichiki (2003) reports that the draw of ecotourism comes from tourists wanting to see animals in their natural environment. Conveniently, brown boobies nest on these protected islands (e.g., Ogasawara Islands, Japan) and its presence be another selling point for tourists with an interest in bird-watching.

• Positive Impacts
• body parts are source of valuable material
• ecotourism ecotourism

Economic Importance for Humans: Negative

There are no known adverse effects of Sula leucogaster on humans.

Conservation Status

Brown boobies are not considered endangered at this time and no programs promoting their conservation are in progress. Brown booby populations are considered globally stable currently.

Additional Links

Encyclopedia of Life

Contributors

Jason Langteau (author), Radford University, Karen Powers (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

Beadell, J., E. Schreiber, R. Schreiber, G. Schenk, P. Doherty. 2003. Survival of Brown Boobies (Sula lecogaster) at Johnston Atoll: A long-term study. The Auk , 120(3): 811-817.

Chaves-Campos,, J., J. Torres. 2002. Distribution of the Brown Booby (Sula leucogaster) in relation to the inclination of terrain. Ornitologia Neotropical , 13: 205-208.

Drummond, H., C. Rodriquez, H. Schwabl. 2008. Do mothers regulate facultative and obligate siblicide by differentially provisioning eggs with hormones?. Journal of Avian Biology , 39(2): 139-143.

Gianuca, D., C. Vooren. 2007. Abundance and behavior of the sally lightfoot crab (Grapsus grapsus) in the colony of the Brown Booby (Sula leucogaster) in the São Pedro and São Paulo Archipelago. Investigaciones Marinas , 35(2): 121-125.

Gilardi, J. 1992. Sex-specific foraging distributions of Brown Boobies in the eastern tropical pacific. Colonial Waterbirds , 15/1: 148-151.

Lewis, S., E. Schreiber, F. Daunt, G. Schenk, S. Wanless, K. Hamer. 2004. Flexible foraging patterns under different time constraints in tropical boobies. Animal Behaviour , 68(6): 1331-1337.

Mack, L., A. Larner. 2009. Fall reporting period August-November 2008. Virginia Birds , 5(2): 9.

Mellink, E., J. Dominguez, J. Luevano. 2001. Diet of eastern pacific Brown Boobies Sula lecogaster brewsteri on Isla San Jorge, north-eastern Gulf of California, and an April comparison with diets in the middle Gulf of Galifornia. Marine Ornithology , 29: 23-28.

Mellink, E. 2000. Breeding of Brown Boobies in the Gulf of California: Seasonality and apparent effects of El Nino. Waterbirds: The international Journey of Waterbird Biology , 23(3): 494-499.

Milius, S. 2003. Sibling Desperado. Science News , 163(7): 102.

Raffaele, H. 1989. A guide to the birds of Puerto Rico and the Virgin Islands . Princeton, NJ: Princeton University Press.

Richardson, O. 2006. Response of epiphytic foraminiferal communities to natural eutrophication in seagrass habitats off Man O'War Cay, Belize. Marine Ecology , 27(4): 404-416.

Schreiber, E., R. Norton. 2002. Brown Booby: Sula leucogaster. The Birds of North America , 17/1: 1-26.

Spennemann, D. 1999. Exploitation of bird plumages in the German Mariana Islands. Micronesica , 31/2: 309-318.

Tershey, B., D. Breese, Croll. 2003. Insurance eggs versus additional eggs: Do Brown Boobies practice obligate siblicide?. The Auk , 117(3): 817-820.

VanderWerf, E., K. Wood, C. Swenson, M. LeGrande, H. Eijzenga, R. Walker. 2007. Avifauna of Lehua Islet, Hawai'i: Conservation value and management needs. Pacific Science , 61(1): 39-52.

Work, T., R. Rameyer. 1997. Description and Epizootiology of Babesia poelea n. sp. in Brown Boobies (Sula leucogaster (Boddaert)) on Sand Island, Johnston Atoll, Central Pacific.. The Journal of Parasitology , 83/4: 734-738.

Yoda, K., H. Kohno, Y. Naito. 2007. Ontogeny of plunge diving behaviour in brown boobies: Application of a data logging technique to hand-raised seabirds. Deep-Sea Research Part II, Topical Studies in Oceanography , 54/3-4: 321-329.

2009. "AnAge Entry for Sula leucogaster" (On-line). AnAge's Bibliographical Database. Accessed April 12, 2010 at http://genomics.senescence.info/species/entry.php?species=Sula_leucogaster .

Ogasawara Whale-watching Association & Bonin Ecotourism Commission. Ecotourism in Ogasawara Islands. 100-2101. Japan: Ogasawara Whale-watching Association & Bonin Ecotourism Commission. 2003. Accessed April 21, 2010 at http://www.airies.or.jp/publication/ger/pdf/07-01-03.pdf .