Sula

Diversity

There are six species of birds known as boobies in the genus Sula . These medium to large seabirds are found in marine and coastal habitats including islands, coastal areas, and temperate, pan-tropical oceans (Lee and Haney, 1984). Boobies vary in size (1000 to 2500 grams), but generally have long wings, a wedge-shaped tail, short and far-set legs, totipalmate feet (four toes with webbing), and a conical bill with a decurved tip (Diaz, Alfredo and Salazar Gomez, 2011). The species within Sula exhibit sexual dimorphism with females often larger than males (Cornell University, 2015). Although physically similar, different species of boobies exhibit unique behaviors and other differences in their ecology. Plumage and bill color varies between species, with some having brightly-colored feet used for mating rituals. Boobies feed primarily on shoaling fish and use a streamlined, powerful, headfirst dive from up to 25 meters in the air into the water to catch prey (National Geographic, 2018). They fold their long wings back to further streamline the body for a more efficient headfirst dive (Diaz, Alfredo and Salazar Gomez, 2011). Species in Sula form pairs during breeding season through ritualized mating performances that show off their webbed feet, although infidelity frequently occurs throughout the large nesting colonies that are formed (Nelson, 1978).

Geographic Range

Sula species live in temperate, pantropical waters across the world. Although nonmigratory, boobies are widely distributed across marine and coastal areas in the Gulf of California, throughout the Caribbean Sea, along the Pacific coast to northern Peru, and west to the Galapagos Islands (Nelson, 1978). The species of Sula are also found on small oceanic islands surrounded by temperate waters in seas north of Australia and throughout the Indian, Pacific, and Atlantic Oceans (Lee and Haney, 1984). On rare occasions, blue-footed boobies ( Sula nebouxii ), masked boobies ( Sula dactylatra ), brown boobies ( Sula leucogaster ), and red-footed boobies ( Sula sula ) have been observed off the Pacific and Atlantic coasts of the United States (Florida and California) (Sibley, 2014).

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

Habitat

The majority of Sula species are solitary marine foragers that return from sea and roost on coral atolls, volcanic islands, coasts, and oceanic islands (Nelson, 1978). Blue-footed boobies ( Sula nebouxii ) and red-footed boobies ( Sula sula ) are occasionally seen foraging in small groups off of rocky islets and shorelines near roosts (Cornell University, 2015). Each species has a unique habitat preference for nesting. The majority of species, excluding red-footed boobies, nest on open, minimally shaded ground. Red-footed boobies are the only arboreal nesters (Nelson, 1969). Different Sula species can be found roosting in the same areas although territorial aggression between different species occurs, resulting in differences in nest site selection. For example, Blue-footed Boobies in the Galapagos Islands nest at coastal sites if Nazca boobies ( Sula granti ) are not present, but blue-footed boobies move further away from ideal nesting habitat when Nazca boobies are present (Townsend et al, 2002).

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

• Aquatic Biomes
• pelagic pelagic
• coastal coastal

Systematic and Taxonomic History

Sula was first named and published in literature by Mathurin-Jacques Brisson in 1760 ("Sula Brisson, 1760", 2017). The taxonomy of boobies and gannets has been a source of disagreement among scientists since the early 1900s. Species in Sula are closely related to gannets in Morus . A segment of the mitochondrial cytochromeb gene was sequenced for all living Sulids, and the parsimony analyses placed gannets and boobies in separate, monophyletic lineages (Friesen and Anderson, 1997). Originally, Sula and Morus made up the Sulidae family (Diaz, Alfredo and Salazar Gomez, 2011). Dorst and Mougin placed all species in Sula in 1930 and were combined back and forth until 1990 (Chaves-Campos and Torres, 2002). In 1988, scientists provided skeletal evidence to separate the gannets and boobies back into Sula and Morus (Diaz, Alfredo and Salazar Gomez, 2011). Further morphological evidence elevated Abbott’s booby from Sula into their own genus, Papasula (Chaves-Campos and Torres, 2002).

Physical Description

Sula species are medium to large birds (800 to 2400 g; 70 to 85 cm long) with wingspans up to five feet long (37.4 to 170 cm) (Nelson, 1978). Boobies are sexually dimorphic, with females generally being larger and weighing more than males. Only one species, the red-footed booby ( Sula sula ) exhibits color polymorphism, with up to five different color morphs (brown, white, black-tailed white, white-tailed brown, and white-headed brown) (Sibley, 2014). Sula species have a variety of plumage colors ranging between white, brown and black. Juveniles tend to have darker brown and black plumage but, as hatchlings they are covered in white down feathers. The often colored (red, blue, gray, yellow, black) totipalmate feet (four webbed toes) of Sula species are set far back on the body. Boobies have desmognathous palates with no exposed outside nares, and nasal grooves running down the stout, conical bill (Nelson, 1978). Adult boobies have bare facial and gular skin (Sibley, 2014). The featherless skin, bill, and feet are colored differently based on the species, which can be red, blue, gray, yellow, or black (Sibley, 2014). Boobies have binocular vision because each eye is situated on either side of the bill. The largest Sula species is the masked booby ( Sula dactylatra ), with males ranging between 1220 and 2211 grams and females ranging between 1470 and 2400 grams ("Sula dactylatra (Masked Booby)", 2016). Red-footed boobies ( Sula sula ) are the smallest Sula species, with males between 800 and 1160 grams and females between 850 and 1210 grams (Sibley, 2014 and Nelson, 1978). Boobies are most closely related to gannets ( Morus ), but have key differences between them. Gannets are monomorphic in size, are migratory, and have feathers extending forward of the eyes, while boobies are sexually dimorphic, sedentary, and have bare facial skin forward from the eyes.

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry
• polymorphic polymorphic

• Sexual Dimorphism
• female larger

Reproduction

Sula species are monogamous, but occasionally partake in infidelity when their mate is out foraging for food on the ocean (Nelson, 1978). As breeding season approaches, male boobies defend a territory and once a female pairs with a male, they jointly choose a breeding site to defend within the male’s territory (Nelson, 1978). Sula males and females perform a complex display to find, attract, and bond with a mate. Sula courtship displays involve exaggerated raising and flaunting of feet to their partner called “parading” (Nelson, 1978). To females, the color of the feet is a good indicator of the male’s physical and reproductive health. The brighter the feet are, the healthier the mate is. Breeding pairs typically practice this courtship display more than once over the breeding season to protect nesting territory and solidify their bond (Diaz, Alfredo and Salazar Gomez, 2011). Both female and male boobies practice extra-pair copulation during fertile periods.

• Mating System
• monogamous monogamous

Boobies nest in colonies and their breeding season can last up to 40 weeks (Nelson, 1978). Breeding season is divided into four main stages: pre-laying, incubation, chick care and post breeding (Nelson, 1978). Pre-laying is comprised of defending nest territories and establishing adequate bonding pair relationships (Nelson, 1978). Clutch sizes range from 1 to 3 eggs (blue to white in color) (Nelson, 1978). Most boobies nest on the ground, excluding red-footed boobies, who nest in trees (Nelson, 1969). The incubation period lasts around 50 days, with both males and females alternating egg incubation (Nelson, 1978). Boobies do not have brooding patches and use their totipalmate feet to transfer heat to the eggs. g. Sula males that doubt the paternity of their egg are known to destroy all of the eggs in the nest (Diaz, Alfredo and Salazar Gomez, 2011).. g. Sula hatchlings are featherless and gradually gain white down feathers (Nelson, 1978). As juveniles, the plumage is dark brown to black (Nelson, 1978). Hatchlings are altricial and require male and female care for an average of 100 days, during which hatchlings are completely dependent on their parents for food and protection (Nelson, 1978). Both parents forage for food in the ocean and regurgitate semi-digested food into the hatchling’s mouth. Nestlings are vulnerable to predators like hawks and short-eared owls during the day when both parents are out foraging (Mellink, Dominguez and Luevano, 2000). In the Galapagos, adult Nazca boobies attack and injure blue-footed booby nestlings to prevent successful fledging (Townsend et al, 2002).

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
• oviparous oviparous

Males and females take turns incubating the eggs by transferring heat from their totipalmate feet (Diaz, Alfredo, and Salazar Gomez, 2011). Each parent guards the nest through the night if the counterpart is out at sea foraging. Once the egg hatches, each parent forages for food for the nestlings (Nelson, 1978). The nestlings are under parental care for approximately 100 days, until they are mature enough to forage for themselves (Nelson, 1978).

• Parental Investment
• altricial altricial
• male parental care male parental care
• female parental care female parental care
• pre-fertilization
  • protecting
    • male
    • female
• pre-hatching/birth
  • provisioning
    • male
    • female
  • protecting
    • male
    • female
• pre-weaning/fledging
  • provisioning
    • male
    • female
  • protecting
    • male
    • female
• pre-independence
  • provisioning
    • male
    • female
  • protecting
    • male
    • female

Lifespan/Longevity

The typical lifespan of boobies is 17 years to a maximum 30 years (Nelson, 1978). The oldest banded brown booby recorded was 27.2 years old (Longevity Records of North American Birds, 2017). Adult mortality rate for boobies is 5-10% (Nelson, 1978). Factors that limit their lifespan include predation on land and sea, pressures from commercial fishing, coastal development, and subsequent habitat destruction (National Geographic, 2018).

Behavior

Boobies are social species that live and breed in colonies. Boobies are piscivores that forage solitarily, in small groups, or in large groups, depending on the species. Sula can dive up to 25 meters deep in the ocean for fish (Cornell University, 2015). Boobies pair up during mating season and perform elaborate rituals showcasing the feet, jabbing bills, and nodding the head (Nelson, 1978). Males of Sula defend small nesting areas and are territorial during breeding season (Diaz, Alfredo and Salazar Gomez, 2011). Agonistic behavior occurs between blue-footed booby siblings (Diaz, Alfredo and Salazar Gomez, 2011). Larger offspring will peck their smaller siblings, causing parents to selectively feed the larger, more dominant (and healthy looking) offspring. This can lead to starvation and death of the smaller sibling (Diaz, Alfredo and Salazar Gomez, 2011). Boobies use calls and body language to communicate.

• Key Behaviors
• flies
• natatorial natatorial
• diurnal diurnal
• motile motile
• sedentary sedentary
• territorial territorial
• colonial colonial

Communication and Perception

Sula species are silent at sea. On breeding grounds, adult males whistle and bray, while females and juveniles vocalize with a deep, duck-like note (Diaz, Alfredo and Salazar Gomez, 2011). Potential mates communicate through elaborate courtship displays, characterized by sky-pointing with beaks, gazing, mutual jabbing, and parading feet (Nelson, 1978). Boobies exhibit aggressive behavior to establish their territory. This includes aerial attacks, wing-flailing, jabbing bill toward their opponent, and head bowing (Nelson, 1969). Sula species do not exhibit social or hierarchical ranking.

• Communication Channels
• visual visual
• acoustic acoustic

• Other Communication Modes
• duets duets

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

Food Habits

Sula species are piscivores that feed on small, pelagic shoaling fishes like anchovies ( Cetengraulis mysticetyus and Engraulis mordax ), sardines ( Sardinops sagax ), mackerels, flying fish ( Exocoetidae ), and squid ( Loliginidae ) (Mellink, Dominguez and Luevano, 2000; and Diaz, Alfredo, and Salazar Gomez, 2011).

• Primary Diet
• carnivore carnivore
  • piscivore piscivore

Predation

Sula species are preyed on by owls ( Strigiformes ), condors ( Cathartidae ), sharks, rats, humans, cats, and gulls ( Laridae ) (Mellink, Dominguez and Luevano, 2000 and Nelson, 1978).

Ecosystem Roles

Sula species are prey to cats, rats, fish, and birds, and are predators to shoaling fish like mackerel, anchovies, flying fish, sardines, and squid (Mellink, Dominguez and Luevano, 2000).

Economic Importance for Humans: Positive

Boobies are of economic importance to tourism industries around the globe. For example, blue-footed boobies frequent the Galapagos and are of interest to tourists. Tourists also visit red-footed boobies that nest on Caribbean islands. Scientists are interested in the ecology and ecosystem roles of boobies. These pelagic birds are indicator species of ocean and ecosystem health. Booby fecal matter, or guano, has historically been used as a crop fertilizer. The demand for guano has increased as a result of the price increase of synthetic fertilizers and upward trend favoring organic produce (Highfield, 2011). Guano is primarily collected on islands off the coast of Peru, and is shipped as far as Europe to fertilize different crops (Highfield, 2011).

• Positive Impacts
• ecotourism ecotourism

Economic Importance for Humans: Negative

There are no known adverse effects of Sula on humans.

Conservation Status

Masked ( Sula dactylatra ), blue-footed ( Sula nebouxii ), brown ( Sula leucogaster ), and red-footed boobies ( Sula sula ) are protected species under the Migratory Bird Treaty Act ("Migratory Bird Treaty Act", 2013). The IUCN Red List classifies all species in Sula as species of least concern ("Sula dactylatra (Masked Booby)", 2016 and "Sula variegata (Peruvian Booby)", 2016). The population numbers of masked, brown, red-footed, and Nazca ( Sula granti ) boobies are decreasing according to the IUCN Red List. Abbott’s booby ( Papasula abbotti ), a species in the the sister genus of Sula , Papasula , is listed on CITES, but no Sula species are listed ("UNEP", 2018). Declines in populations are attributed to food scarcity caused by overfishing, and coastal habitat fragmentation and loss (National Geographic, 2018).

Other Comments

Species in Sula are thought to get their common name, “booby” from the Spanish word “bobo”. The term translates to “stupid” in English and is thought to be representative of the clumsy, goofy walk the booby exhibits on land (National Geographic, 2018).

Additional Links

Encyclopedia of Life

Contributors

Makenna Spencer (author), Colorado State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

Chaves-Campos, J., J. Torres. 2002. Distribution of Nests of the Brown Booby (Sula Leucogaster) in Relation to the Inclination of Terrain. Ornitologia Neotropical , 13: 205-208. Accessed January 31, 2018 at http://www.avibirds.com/pdf/B/Bruine%20Gent5.pdf .

Diaz, H., J. Alfredo, E. Salazar Gomez. 2011. "Neotropical Birds Online" (On-line). Blue-footed Booby (Sula nebouxii). Accessed February 11, 2018 at https://neotropical.birds.cornell.edu/Species-Account/nb/species/bfoboo/overview .

Friesen, V., D. Anderson. 1997. Phylogeny and Evolution of the Sulidae (Aves: Pelecaniformes): A Test of Alternative Modes of Speciation. Elsevier , Volume 7, Issue 2: 252-260. Accessed January 31, 2018 at https://www-sciencedirect-com.ezproxy2.library.colostate.edu/science/article/pii/S1055790396903978?_rdoc=1&_fmt=high&_origin=gateway&_docanchor=&md5=b8429449ccfc9c30159a5f9aeaa92ffb&ccp=y .

Highfield, R. 2011. The New Guano Era. New Scientist , Vol. 212 Issue 2842: 26-27.

Lee, D., J. Haney. 1984. The Genus Sula in the Carolinas: An Overview of the Phenology and Distribution of Gannets and Boobies in the South Atlantic Bight. Chat , Vol. 41, No. 2: 29-45. Accessed January 31, 2018 at https://www.carolinabirdclub.org/chat/issues/1984/v48n2sula.pdf .

Mellink, E., J. Dominguez, J. Luevano. 2000. Diet of Eastern Pacific Brown Boobies Sula Leucogaster Brewsteri on Isla San Jorge, North-eastern Gulf of California, and an April Comparison with Diets in the Middle Gulf of California. Marine Ornithology , 29: 29-38. Accessed March 01, 2018 at http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.669.9553&rep=rep1&type=pdf .

Nelson, B. 1978. The Sulidae: Gannets and Boobies . Aberdeen, UK: University of Aberdeen.

Nelson, J. 1969. The Breeding Ecology of the Red-footed Booby in the Galapagos. Journal of Animal Ecology , Vol. 38, No. 1: 181-198. Accessed January 31, 2018 at http://www.jstor.org.ezproxy2.library.colostate.edu/stable/2745?sid=primo&origin=crossref&seq=1#page_scan_tab_contents .

Sibley, D. 2014. The Sibley Guide to Birds 2nd Edition . New York: Alfred A. Knopf.

Townsend, H., K. Huyvaert, P. Hodum, D. Anderson. 2002. Nesting Distributions of Galápagos Boobies (Aves: Sulidae): An Apparent Case of Amensalism. Oecologica , Vol. 132, No. 3: 419-427. Accessed January 31, 2018 at http://www.jstor.org.ezproxy2.library.colostate.edu/stable/4223357?seq=1#page_scan_tab_contents .

Weimerskirch, H., S. Shaffer, Y. Tremblay, D. Costa, H. Gadenne, A. Kato, Y. Ropert-Coudert, K. Sato, D. Aurioles. 2009. Species- and sex-specific differences in foraging behaviour and foraging zones in blue-footed and brown boobies in the Gulf of California. Marine Ecology Process Series , Volume 391: 267-278. Accessed January 31, 2018 at http://www.jstor.org/stable/24873671 .

Cornell University. 2015. "Blue-footed Booby" (On-line). The Cornell Lab of Ornithology All About Birds. Accessed January 31, 2018 at https://www.allaboutbirds.org/guide/Blue-footed_Booby/id .

USGS. 2017. "Longevity Records of North American Birds" (On-line). Accessed February 26, 2018 at https://www.pwrc.usgs.gov/bbl/longevity/Longevity_main.cfm .

2013. "Migratory Bird Treaty Act" (On-line). U.S. Fish and Wildlife Service. Accessed February 28, 2018 at https://www.fws.gov/birds/management/managed-species/migratory-bird-treaty-act-protected-species.php .

National Geographic. 2018. "Red-footed Booby" (On-line). Accessed February 26, 2018 at https://www.nationalgeographic.com/animals/birds/r/red-footed-booby/ .

2017. "Sula Brisson, 1760" (On-line). Integrated Taxonomic Information System (ITIS). Accessed February 11, 2018 at https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&anchorLocation=SubordinateTaxa&credibilitySort=Subordinate%20Taxa&rankName=Subspecies&search_value=174697&print_version=SCR&source=from_print#SubordinateTaxa .

2016. "Sula dactylatra (Masked Booby)" (On-line). The IUCN Red List of Endangered Species. Accessed January 31, 2018 at http://www.iucnredlist.org/details/22736173/0 .

2016. "Sula variegata (Peruvian Booby)" (On-line). The IUCN Red List of Endangered Species. Accessed January 31, 2018 at http://www.iucnredlist.org/details/22696686/0 .

2018. "UNEP" (On-line). The Species+ Website. Accessed February 28, 2018 at https://speciesplus.net/#/taxon_concepts/6600/references .