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Booby
View on Wikipediafrom Wikipedia
| Booby Temporal range: Miocene (Langhian) – recent[1]
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|---|---|
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| Blue-footed booby displaying by raising a foot | |
Scientific classification 
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| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Suliformes |
| Family: | Sulidae |
| Genus: | Sula Brisson, 1760 |
| Type species | |
| Pelecanus leucogaster Boddaert, 1783
| |
A booby is a seabird in the genus Sula, part of the family Sulidae. Boobies are closely related to the gannets (Morus), which were formerly included in Sula.
Systematics and evolution
[edit]
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| Cladogram showing the species in the genus Sula.[2] |
The genus Sula was introduced by the French zoologist Mathurin Jacques Brisson in 1760.[3] The type species is the brown booby.[4] The name is derived from súla, the Old Norse and Icelandic word for the other member of the family Sulidae, the gannet.[5]
The English name booby may derive from the Spanish slang term bobo, meaning "stupid",[6] as these tame birds had a habit of landing on board sailing ships, where they were easily captured and eaten. Owing to this, boobies are often mentioned as having been caught and eaten by shipwrecked sailors, including William Bligh of the Bounty and his adherents during their voyage after being set adrift by Fletcher Christian and his followers.[7]
Six of the ten extant Sulidae species called boobies are in the genus Sula, while the three gannet species are usually placed in the genus Morus.[8] Abbott's booby was formerly included in Sula but is now placed in a monotypic genus Papasula, which represents an ancient lineage perhaps closer to Morus. Some authorities consider that all ten species should be considered congeneric in Sula. However, they are readily distinguished by means of osteology. The distinct lineages of gannets and boobies are known to have existed in such form, since at least the Middle Miocene (15 mya).[9]
The fossil record of boobies is not as well documented as that of gannets, either because booby speciation was lower from the late Miocene to the Pliocene (when gannet diversity was at its highest), or because the booby fossil species record is as yet incomplete due to most localities being equatorial or in the Southern Hemisphere.
Behaviour
[edit]Boobies hunt fish by diving from a height into the sea and pursuing their prey underwater. Facial air sacs under their skin cushion the impact with the water. Boobies are colonial breeders on islands and coasts. They normally lay one or more chalky-blue eggs on the ground or sometimes in a tree nest. Selective pressures, likely through competition for resource, have shaped the ecomorphology and foraging behaviours of the six species of boobies in the Pacific.[10]
List of species
[edit]| Common name | Scientific name and subspecies | Range | Size and ecology | IUCN status and estimated population |
|---|---|---|---|---|
| Blue-footed booby
|
Sula nebouxii Milne-Edwards, 1882 Two subspecies
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Gulf of California down along the western coasts of Central and South America down to Peru_world2.png)
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Size: Habitat: Diet: |
LC |
| Brown booby
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Sula leucogaster (Boddaert, 1783) Four subspecies
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Islands and coasts in the pantropical areas of the Atlantic and Pacific oceans
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Size: Habitat: Diet: |
LC |
| Cocos booby
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Sula brewsteri Goss, 1888 Four subspecies
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East and Central Pacific
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Size: Habitat: Diet: |
NE
|
| Masked booby
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Sula dactylatra Lesson, 1831 Four subspecies
|
islands in tropical oceans
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Size: Habitat: Diet: |
LC |
| Nazca booby
|
Sula granti Rothschild, 1902 |
Eastern Pacific from the islands in Baja California to the Galapagos islands and the Isla de la Plata in Ecuador and Malpelo in Colombia
|
Size: Habitat: Diet: |
LC |
| Peruvian booby
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Sula variegata (Tschudi, 1843) |
Peru
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Size: Habitat: Diet: |
LC |
| Red-footed booby
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Sula sula (Linnaeus, 1766) Three subspecies
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Sri Lanka, Christmas Island, eastern central Pacific
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Size: Habitat: Diet: |
LC |
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References
[edit]- ^ "Sula Brisson 1760 (booby)". PBDB. Archived from the original on 2021-08-08. Retrieved 2019-07-08.
- ^ Patterson, S.A.; Morris-Pocock, J.A.; Friesen, V.L (2011). "A multilocus phylogeny of the Sulidae (Aves: Pelecaniformes)". Molecular Phylogenetics and Evolution. 58 (2): 181–191. Bibcode:2011MolPE..58..181P. doi:10.1016/j.ympev.2010.11.021. PMID 21144905.
- ^ Brisson, Mathurin Jacques (1760). Ornithologie, ou, Méthode contenant la division des oiseaux en ordres, sections, genres, especes & leurs variétés (in French and Latin). Vol. 1. Paris: Jean-Baptiste Bauche. Vol. 1 p. 60, Vol. 6 p.494.
- ^ Mayr, Ernst; Cottrell, G. William, eds. (1979). Check-list of Birds of the World. Vol. 1 (2nd ed.). Cambridge, Massachusetts: Museum of Comparative Zoology. p. 181. Archived from the original on 2021-08-08. Retrieved 2017-11-21.
- ^ "Sula, n.". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
- ^ "booby, n.". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
- ^ Alexander, Caroline (25 May 2004). The Bounty: The True Story of the Mutiny on the Bounty. Penguin Books. ISBN 978-0-14-200469-2.
- ^ Friesen, V. L.; Anderson, D. J.; Steeves, T.E.; Jones, H.; Schreiber, E.A. (2002). "Molecular support for species status of the Nazca Booby". The Auk. 119 (3): 820–826. doi:10.1642/0004-8038(2002)119[0820:MSFSSO]2.0.CO;2. S2CID 82903466.
- ^ Olson, Storrs L. (1985). "The Fossil Record of Birds (Section X.G.5.a Sulidae)". In Farner, D.S.; King, D.S.; Parkes, K.C. (eds.). Avian Biology. Vol. 8. New York: Academic Press. pp. 79–238 [203–204]. hdl:10088/6553. Archived from the original on 2021-04-10. Retrieved 2017-11-22.
- ^ van Oordt, F.; Torres-Mura, J. C.; Hertel, F. (2018). "Ecomorphology and foraging behaviour of Pacific boobies". Ibis. 160 (2): 313–326. doi:10.1111/ibi.12545. hdl:20.500.14005/3968.
- ^ BirdLife International (2018). "Sula nebouxii". IUCN Red List of Threatened Species. 2018 e.T22696683A132588719. doi:10.2305/IUCN.UK.2018-2.RLTS.T22696683A132588719.en. Retrieved 13 November 2021.
- ^ BirdLife International (2018). "Sula leucogaster". IUCN Red List of Threatened Species. 2018 e.T22696698A132590197. doi:10.2305/IUCN.UK.2018-2.RLTS.T22696698A132590197.en. Retrieved 13 November 2021.
- ^ BirdLife International (2018). "Sula dactylatra". IUCN Red List of Threatened Species. 2018 e.T22736173A132666363. doi:10.2305/IUCN.UK.2018-2.RLTS.T22736173A132666363.en. Retrieved 13 November 2021.
- ^ BirdLife International (2018). "Sula granti". IUCN Red List of Threatened Species. 2018 e.T22728990A132659882. doi:10.2305/IUCN.UK.2018-2.RLTS.T22728990A132659882.en. Retrieved 13 November 2021.
- ^ BirdLife International (2018). "Sula variegata". IUCN Red List of Threatened Species. 2018 e.T22696686A132589026. doi:10.2305/IUCN.UK.2018-2.RLTS.T22696686A132589026.en. Retrieved 13 November 2021.
- ^ BirdLife International (2018). "Sula sula". IUCN Red List of Threatened Species. 2018 e.T22696694A132589278. doi:10.2305/IUCN.UK.2018-2.RLTS.T22696694A132589278.en. Retrieved 13 November 2021.
External links
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Booby
View on Grokipediafrom Grokipedia
Boobies are seabirds comprising the genus Sula within the family Sulidae, encompassing six species of medium to large piscivorous and squid-eating marine birds primarily distributed across tropical and subtropical oceans worldwide.[1] These birds are renowned for their spectacular plunge-diving foraging behavior, in which they soar to heights of up to 30 meters before folding their long, narrow wings and arrowing into the water at speeds exceeding 60 km/h to pursue prey near the surface.[2] Ranging in size from 64 to 90 cm in length and weighing 700 to 2,200 g, boobies exhibit sexual dimorphism with females typically larger and heavier than males, and they possess stout, pointed bills, streamlined bodies, and elongated wings adapted for efficient aerial and underwater locomotion.[3]
The genus Sula is part of the Sulidae family, which totals 10 species including the four gannet species in the genus Morus, but boobies are distinguished by their more equatorial habitats and often vibrant, species-specific foot colors—such as blue in Sula nebouxii, red in Sula sula, or yellow in Sula dactylatra—that play key roles in elaborate courtship displays and mate attraction.[4][5] Boobies are strictly pelagic outside of breeding season, spending most of their lives over open ocean but returning to nest in dense colonies on remote islands, cliffs, or mangroves, where they construct nests from sticks, guano, or simply scrape ground depressions depending on the species.[6] Their diet consists mainly of small schooling fish like anchovies and sardines, supplemented by squid and flying fish, which they capture through coordinated group foraging or solitary dives.[2]
Reproduction in boobies is highly colonial and seasonal, with pairs forming long-term bonds and engaging in ritualized displays, including sky-pointing, bill-clacking, and foot-flashing, to synchronize breeding; eggs (typically 1–3 per clutch) are incubated by both parents using their broad, webbed feet, which enhances heat regulation in hot climates.[3] While most species are ground- or bush-nesters, the red-footed booby (Sula sula) is arboreal, building twig platforms high in trees, and some like the brown booby (Sula leucogaster) are known for ground-nesting in exposed sites.[7] Conservation concerns vary by species, with the blue-footed booby (Sula nebouxii) facing threats from habitat loss and invasive predators on breeding islands, though overall the genus remains relatively secure due to their wide oceanic ranges.[8]
The red-footed booby has three subspecies (S. s. sula, S. s. rubripes, S. s. websteri), distinguished by plumage variations and geographic isolation across ocean basins. The brown booby has two subspecies (S. l. leucogaster, S. l. plotus), reflecting adaptations to different tropical regions. The Cocos booby has three subspecies (S. b. brewsteri, S. b. etesiaca, S. b. nesiotes), varying by location in the eastern Pacific. The masked booby includes four subspecies (S. d. dactylatra, S. d. personata, S. d. tasmani, S. d. melanops), varying in bill color and size. The blue-footed booby has two subspecies (S. n. nebouxii, S. n. excisa), with the latter endemic to the Galápagos. The Nazca, Peruvian, and Abbott's boobies each lack recognized subspecies. The Nazca booby was recognized as distinct from the masked booby in 2000 due to differences in plumage, vocalizations, and genetics. The Cocos booby was recognized as distinct from the brown booby in 2024 based on morphological, genetic, and behavioral evidence.
Fossil records include prehistoric boobies such as Papasula abbotti costelloi from the late Holocene on Ua Huka (French Polynesia), extinct due to human activity.[101]
Taxonomy and systematics
Classification
Boobies are classified within the family Sulidae, which encompasses both gannets and boobies, and the order Suliformes, previously included under Pelecaniformes before taxonomic revisions based on molecular phylogenetics restructured the order in 2010.[9] The primary genus for boobies is Sula, comprising approximately seven recognized species: the red-footed booby (Sula sula), brown booby (Sula leucogaster), blue-footed booby (Sula nebouxii), masked booby (Sula dactylatra), Nazca booby (Sula granti), Peruvian booby (Sula variegata), and Cocos booby (Sula brewsteri).[10] These species are distinguished from gannets, now placed in the genus Morus, through historical taxonomic revisions that separated the genera in the late 20th century, relying on morphological differences such as skeletal structure in the cranium, sternum, and pelvis, as well as genetic evidence from DNA sequencing.[11] Species recognition within Sula is supported by criteria including genetic divergence, particularly in mitochondrial DNA analyses, where interspecies differences typically range from 2-5% in cytochrome b sequences, indicating sufficient isolation for full species status, as seen in the split of the Nazca booby from the masked booby. Subspecies classifications further refine this taxonomy; for instance, the brown booby (Sula leucogaster) includes the subspecies Sula leucogaster leucogaster (Atlantic and Caribbean populations) and Sula leucogaster plotus (Indo-Pacific populations), which exhibit minor differences in distribution and plumage adapted to regional conditions. Recent taxonomic revisions, such as the 2024 split of the Cocos booby (Sula brewsteri, including subspecies like etesiaca) from the brown booby complex based on morphology and genetics, highlight ongoing refinements within the genus.[12][13]Evolution
The boobies (genus Sula) within the family Sulidae originated during the Miocene epoch, approximately 23 to 5 million years ago, with the earliest definitive fossils of the genus appearing in early Miocene deposits along the Pacific coast of South America, such as those from the Chilcatay Formation in Peru. Earlier Sulidae fossils, including possible stem-group representatives, date to the late Oligocene in Europe (e.g., Sula ronzoni from France), but unambiguous Sula records are confined to the Miocene in both Europe and North America, indicating a gradual diversification of plunge-diving seabirds in expanding marine environments. The adaptive radiation of Sulidae, including boobies, is linked to the post-Cretaceous-Paleogene (K-Pg) extinction event around 66 million years ago, which decimated marine reptile predators and allowed for the proliferation of teleost fish populations and open-ocean ecosystems that favored specialized piscivores. This ecological vacancy enabled Sulidae to evolve advanced dive-fishing adaptations, with boobies representing a derived clade specialized for deep-water pursuits. Phylogenetic analyses within the order Suliformes position boobies as sister to gannets (Morus), with molecular clock estimates indicating their divergence occurred around 20–25 million years ago in the early Miocene, supported by fossil-calibrated Bayesian models. Key evolutionary traits in boobies, such as streamlined bodies and robust skeletal structures for aerial plunges, are evident in comparative anatomy of Miocene Sulidae fossils, including partial humeri and coracoids assigned to Sula from North American and European deposits that show elongated wing elements adapted for high-speed dives. Speciation events in boobies have been influenced by ocean currents and island formation, which created vicariant barriers and promoted genetic isolation among tropical and subtropical populations, as seen in phylogeographic patterns across the Pacific and Atlantic.Physical description
Morphology
Boobies, members of the genus Sula within the family Sulidae, are medium to large seabirds exhibiting a streamlined, cigar-shaped body adapted for aerial and aquatic locomotion. They typically measure 70–90 cm in length, with wingspans ranging from 130–170 cm and body weights between 0.8–2.4 kg across species.[14] Sexual size dimorphism is pronounced, with females generally 10–20% larger and heavier than males, influencing overall proportions and mass distribution.[3] Key morphological features include a long, pointed, dagger-like bill that is stout and conical, often with serrated edges in certain species for securing prey. The wings are long and narrow, positioned far back on the body to facilitate dynamic soaring over open water, while the tail is short and wedge-shaped for maneuverability. Legs are short and set posteriorly, supporting a primarily pelagic lifestyle, and the feet are fully webbed (totipalmate), with all four toes connected by extensive webbing to enhance swimming efficiency.[1][3] Skeletal and soft-tissue adaptations enable boobies to withstand the rigors of plunge-diving from heights up to 30 m. These include robust neck musculature and a flexible yet stable vertebral column that absorbs impact forces, reducing injury risk during high-speed water entry.[15] Subcutaneous air sacs, particularly prominent around the head and neck, provide cushioning against deceleration, while the overall pneumatic skeletal system aids in buoyancy management during brief underwater pursuits.[16] Morphological variations occur across species, notably in leg length and foot webbing extent; for instance, the blue-footed booby (Sula nebouxii) possesses relatively longer legs than congeners, which can accentuate certain structural traits when combined with species-specific coloration. Juvenile boobies undergo distinct developmental stages, beginning as downy chicks covered in thick, insulating natal down for thermoregulation, transitioning to a mottled juvenile plumage that is typically darker and less refined than the adult form before reaching maturity.[3]Plumage and coloration
Adult boobies in the genus Sula generally display predominantly white body plumage in maturity, contrasted by dark brown to black flight feathers on the wings and tail, a pattern observed across several species. For instance, the masked booby (Sula dactylatra) features a clean white head, neck, and underbody with black primaries, secondaries, and tail feathers, while the Nazca booby (Sula granti) shares a similar mostly white adult plumage accented by black remiges and rectrices.[17][18] In contrast, the brown booby (Sula leucogaster) exhibits chocolate-brown upperparts and a sharply demarcated white belly, with the upperwing coverts matching the back in tone.[19] The red-footed booby (Sula sula) shows plumage polymorphism, with a white morph displaying overall white feathering except for dark flight feathers and a brown morph featuring entirely dark brown plumage, though both share a white tail.[20] Species-specific coloration in bare parts further distinguishes boobies, particularly in the feet and facial regions. The blue-footed booby (Sula nebouxii) is notable for its bright blue feet, resulting from carotenoid pigments derived from its diet of fresh fish, which concentrate in the skin to produce the aquamarine hue.[21] Conversely, the red-footed booby's coral-red feet arise from carotenoid pigments derived from their diet, with the feet also being highly vascularized to facilitate heat transfer during incubation.[22] The masked booby bears a striking black facial mask encompassing the eyes and extending to the bill base, enhancing its distinctive appearance. Additional bare skin features include orbital rings, which vary from blue in some species like the blue-footed booby to yellow in others such as the masked booby. Boobies also possess inflatable gular pouches beneath the bill, which aid in thermoregulation by allowing evaporative cooling through rapid fluttering during heat stress.[23] Juvenile boobies undergo ontogenetic changes in plumage, starting with downy white natal covering that is replaced by mottled brown-gray feathers within weeks. For example, young masked boobies display dark chocolate-brown overall plumage with a white collar on the upper back and white breast, gradually lightening over time.[17] This transitional phase persists for 1-3 years, during which scattered adult-like white feathers appear amid the brownish tones, culminating in full adult coloration.[24] Adults typically molt annually in a pre-breeding cycle, replacing body feathers and some wing coverts to refresh their appearance ahead of the reproductive season.[25] These diverse plumage patterns and bare part colorations within the genus Sula serve to facilitate species recognition, as the unique combinations—such as foot hues and facial masks—allow for visual differentiation among sympatric species.[19]Distribution and habitat
Geographic range
Boobies of the genus Sula exhibit a predominantly pantropical distribution, occurring across the Pacific, Atlantic, and Indian Oceans between approximately 30°N and 30°S latitude.[26] This range encompasses tropical and subtropical marine environments, where the birds forage over open oceans and breed on remote islands. The genus is well-represented in oceanic archipelagos, with breeding colonies concentrated on predator-free or low-disturbance sites.[27] Among the species, the brown booby (Sula leucogaster) has the broadest core range, occurring widely in all three major ocean basins, including the eastern Pacific from Mexico to Peru, the Indo-Pacific from Hawaii to Australia, and the Atlantic and Caribbean from the Gulf of Mexico to Ascension Island. In 2024, the American Ornithological Society split the brown booby complex, recognizing the Cocos booby (Sula brewsteri) as a separate species endemic to Cocos Island off Costa Rica.[27][28] In contrast, the blue-footed booby (Sula nebouxii) is restricted to the eastern Pacific, breeding on islands from northern Peru through the Galápagos Archipelago to Mexico's Baja California and Gulf of California regions.[29] The red-footed booby (Sula sula), meanwhile, favors Indo-Pacific islands, with a pantropical presence extending to the Caribbean, Atlantic, and Pacific, including key sites in the Hawaiian Islands and seas north of Australia.[30] The masked booby (Sula dactylatra) mirrors the pantropical pattern, nesting on hundreds of islands across tropical oceans.[26] Boobies utilize over 100 major breeding colonies worldwide, often on isolated oceanic islands suitable for nesting in open, flat terrains.[27] For instance, Ascension Island in the South Atlantic hosts significant masked booby populations, while the brown booby has an estimated global breeding population of 70,000–100,000 pairs (as of 2024) dispersed among numerous sites.[26][31] Vagrant records occasionally extend beyond core ranges, such as masked booby sightings in Europe, including reports from the United Kingdom.[32] Historical range expansions for several species have been facilitated by the eradication of human-introduced rats on previously colonized islands, allowing recolonization and population recovery.[33] These patterns are influenced by habitat availability on remote islands with minimal terrestrial vegetation and access to productive marine foraging grounds.[27] Recent observations as of 2024 indicate potential range expansions northward for species like the brown and blue-footed boobies, possibly driven by climate change and shifts in prey distribution.[34]Habitat preferences
Boobies, members of the genus Sula in the family Sulidae, exhibit a strong preference for tropical and subtropical marine waters, where they exploit nutrient-rich upwelling zones teeming with fish prey. These zones, such as the Humboldt Current off the coast of Peru, provide optimal foraging opportunities for species like the Peruvian booby (S. variegata) and blue-footed booby (S. nebouxii), enhancing productivity through cold, nutrient-laden waters that support dense schools of small fish.[35][36] They are strictly marine birds, avoiding freshwater systems and cold-water habitats beyond subtropical latitudes, as their physiology is tuned to warm oceanic conditions typically between 20°C and 30°C sea surface temperatures.[37][38] For nesting, boobies select remote oceanic islands, atolls, and coral cays characterized by sparse vegetation and minimal terrestrial predator presence, favoring ground-level sites over mainland coasts to reduce threats from mammals like foxes or rats. These isolated locations, often at elevations from sea level to around 100 m, allow for large colonies while providing proximity to productive offshore waters; for instance, brown boobies (S. leucogaster) commonly nest on open coral atolls or low volcanic stacks in the tropical Pacific and Atlantic.[2][38] In foraging, boobies target surface waters to depths of 10–20 m over coral reefs, continental shelves, or pelagic zones, using plunge dives to pursue epipelagic fish and squid. This shallow diving range aligns with their preference for warm, stratified waters where prey aggregates near the surface, and they show sensitivity to sea surface temperature fluctuations that could alter prey distribution. Adaptations such as supraorbital nasal salt glands enable efficient excretion of excess salt ingested from seawater and marine prey, facilitating prolonged residence in saline marine environments without dehydration.[39][40][41]Behavior and ecology
Foraging and diet
Boobies primarily feed on small schooling fish such as anchovies, sardines, and mackerel, along with squid, which together comprise 80-90% of their diet by mass; occasional crustaceans like shrimp and prawns supplement this intake.[42][43][44] These prey items are targeted in pelagic waters where they form dense schools, allowing boobies to exploit predictable aggregations influenced by ocean currents and upwelling. As secondary predators in marine food webs, boobies occupy a mid-trophic level, preying on herbivores and small carnivores while serving as prey for larger piscivores like tuna.[35][45] Foraging typically involves high-altitude soaring up to 30 meters above the water surface to scan for prey, followed by steep vertical plunge-dives at speeds of 60-100 km/h, enabling submersion to depths of 1-5 meters to pursue targets.[46][47][48] These dives are powered by strong neck muscles and air sacs that cushion impact, with birds using their keen eyesight to detect schools from afar. Daily foraging ranges extend 50-200 km from breeding colonies, with activity following diurnal patterns that peak around dawn and dusk when prey schools are most active near the surface.[49][50][51] During breeding, boobies increase energy demands, consuming prey equivalent to 20-30% of their body weight daily to support chick provisioning and maintain condition.[52] Interspecific differences in foraging are evident, particularly in the red-footed booby, which incorporates a higher proportion of flying fish into its diet through aerial pursuits, snatching them mid-flight rather than relying solely on dives.[53] This arboreal species often forages farther offshore than plunge-diving relatives like the blue-footed or masked boobies, adapting to tropical conditions where flying fish escape predators by leaping from the water.[54][55]Breeding and reproduction
Boobies in the genus Sula exhibit breeding seasonality that varies by species and location, often occurring year-round in tropical regions with peaks during the dry season to align with prey availability.[56] Clutch sizes typically range from 1 to 3 eggs, with most species laying 1–2 chalky-white or blue-tinged eggs at intervals of 4–6 days.[1] Incubation lasts 40–45 days on average, performed biparentally using the broad webs of their feet to cover and warm the eggs, as boobies lack brood patches.[57] Nests are simple scrapes on the ground, often lined with guano, pebbles, or sparse vegetation such as twigs and grass, though red-footed boobies may nest in trees using similar materials.[38] Breeding occurs in dense colonies, with site densities reaching up to 3,300 pairs per hectare in some locations, facilitating synchronous reproduction and predator defense but increasing competition for space.[58] Boobies maintain mostly monogamous mating systems, forming serial pair bonds that can last multiple seasons, though divorce rates vary from 10–40% across species, often driven by female choice for better provisioning partners.[59] Courtship involves elaborate displays, including high-stepping foot parades by males to showcase coloration, such as the bright blue feet of blue-footed boobies (Sula nebouxii), which signal health and attract mates. Parental investment is biparental throughout the reproductive cycle, with both sexes sharing incubation and guarding duties; males often provision more fish to chicks due to their foraging efficiency on smaller prey items.[57] Chicks fledge after 90–120 days in the nest, remaining dependent on parents for an additional 4–6 months post-fledging, during which adults continue to feed them at sea to build foraging skills.[60] Annual fecundity averages 0.5–1 fledgling per breeding pair, reflecting high chick mortality from siblicide or starvation in multi-egg clutches.[61] El Niño events significantly reduce reproductive success by up to 50% through warmer sea temperatures that deplete fish stocks, leading to deferred breeding, smaller clutches, and lower fledging rates.[61]Social structure
Boobies are highly social seabirds that typically form dense colonies during the breeding season but maintain loose aggregations for roosting and foraging during non-breeding periods.[62] Non-breeding juveniles often roost together in large numbers, while adults may join smaller groups at resting sites near foraging areas. Hierarchies at foraging sites are influenced by arrival order, with earlier arrivals securing preferred positions for plunge-diving into prey schools.[63] Communication among boobies involves a range of vocalizations and displays to coordinate group activities and defend resources. For instance, honking calls are used to signal territory defense and deter intruders, while sky-pointing displays—where a bird raises its bill skyward—serve to assert dominance or maintain spacing within flocks. Bill-clattering, a rapid snapping of the bill, occurs during aggressive interactions to intimidate rivals at shared roosts or feeding grounds.[64][65] Kleptoparasitism is a common interspecific interaction for boobies, particularly with frigatebirds, which pursue returning foragers in aerial chases to force regurgitation of food; attacks peak near dusk when boobies approach colonies. Boobies counter these raids by executing evasive steep dives into the water or vocalizing aggressively to ward off harassers. Occasional intra-species food theft also occurs, where dominant individuals steal catches from subordinates during group foraging.[66][67] Boobies frequently engage in group foraging, forming loose flocks of 10–50 individuals that follow tuna schools herding prey to the surface, allowing enhanced prey detection through collective visual cues from diving conspecifics or mixed-species assemblages.[68] These flocks improve foraging efficiency by concentrating efforts on ephemeral prey patches but dissolve quickly after feeding bouts. Alloparenting is rare among boobies but has been observed in red-footed booby colonies, where non-parental helpers—often immature siblings—assist in provisioning and guarding chicks to support family units under variable food conditions.[69]Conservation
Threats and challenges
Booby populations face significant threats from invasive predators on breeding islands, where rats and cats prey heavily on eggs and chicks. In ground-nesting species like the brown booby, feral cats have been documented killing multiple individuals per season, contributing to high chick mortality rates of up to 95% in affected seabird colonies.[70] Invasive rats similarly suppress breeding success by preying on chicks, with studies showing near-total losses in unprotected sites.[71] These predators, introduced by human activity, exacerbate habitat loss by altering island ecosystems and reducing recruitment in booby colonies.[71] Climate variability, particularly El Niño events, disrupts booby foraging by reducing fish stocks through altered ocean currents and warmer sea surface temperatures. During the 1997-1998 El Niño, sardine populations collapsed around the Galápagos, leading to chronic breeding failures and a halving of productivity in Nazca booby colonies.[72] Similar impacts occurred in the 1982-1983 event, where blue-footed booby populations declined by 50% due to food shortages.[73] These events force shifts to lower-quality prey, resulting in widespread nest abandonment and population declines.[74] Human activities pose direct risks through bycatch, egg collection, and guano mining. Longline fisheries incidentally hook thousands of boobies annually, with global seabird bycatch estimates exceeding 160,000 individuals, including significant numbers of masked and brown boobies in tropical waters.[75] Egg harvesting from colonies, particularly in the Pacific and Indian Oceans, reduces reproductive output and disturbs breeding sites.[76] Guano mining on islands like those off Peru disrupts Peruvian booby colonies by damaging nesting grounds and causing adult abandonment.[77] Pollution affects boobies via plastic ingestion and contaminant accumulation. Plastics, mistaken for prey, have been found in the stomachs of brown booby chicks.[78] In some necropsies of tropical seabirds, including boobies, plastics comprise notable portions of gut contents, leading to obstruction and reduced foraging efficiency.[79] Heavy metals bioaccumulate in booby tissues through marine food chains, with elevated levels reported in feather and blood samples from polluted regions, impairing reproduction and survival.[80] Natural threats include hurricanes, which destroy nests and flood colonies. Hurricane Hugo in 1989 caused over 300 red-footed boobies to abandon nesting due to vegetation loss and site damage in the Virgin Islands.[81] Dense colonies are also vulnerable to avian diseases, though specific outbreaks like cholera are less documented in boobies compared to waterfowl.Status and protection
The global population of boobies in the genus Sula is estimated to number in the millions of individuals across all species, with the red-footed booby (S. sula) alone comprising approximately 1.4 million mature individuals.[71] Overall, populations remain stable for most species, though declines have been noted in at least three, including the red-footed booby due to habitat loss and invasive predation. Recent surveys indicate positive developments, such as the red-footed booby population at Aldabra Atoll increasing to over 45,000 pairs as of 2023, the largest in the Indian Ocean.[82] The blue-footed booby (S. nebouxii) has shown localized declines, particularly in the Galápagos Islands where breeding pairs dropped from around 20,000 in the 1960s to approximately 6,400 as of 2012, though its global trend is considered stable with ongoing decreases.[83][84] According to the IUCN Red List, the majority of booby species are classified as Least Concern, reflecting their large ranges and relatively robust populations, such as the brown booby (S. leucogaster) with over 200,000 individuals.[85] Conservation efforts for boobies include the designation of critical breeding sites as Ramsar wetlands, such as the Galápagos Islands, which protect habitats for species like the blue-footed and Nazca boobies (S. granti). Since 2000, invasive species eradication programs on over 20 islands worldwide have benefited seabird populations, including boobies, by reducing predation and improving nesting success rates by up to 40% in targeted areas.[86] International agreements under the Convention on Migratory Species (CMS) provide coverage for migratory booby populations, such as the red-footed booby, promoting coordinated protection across range states.[87] Additionally, fishery regulations mandating circle hooks in longline fisheries have reduced seabird bycatch, including boobies, by minimizing hook ingestion and entanglement.[88] Ongoing monitoring is conducted through annual censuses and surveys by organizations like BirdLife International and Partners in Flight, which track population trends and inform conservation actions.[84] Recovery plans exist for vulnerable species, including a national plan for the masked booby (S. dactylatra) in key sites like Ascension Island to address overfishing impacts.[89]Species
Diversity
The genus Sula includes seven extant booby species: the blue-footed booby (S. nebouxii), Peruvian booby (S. variegata), masked booby (S. dactylatra), Nazca booby (S. granti), brown booby (S. leucogaster), red-footed booby (S. sula), and Cocos booby (S. brewsteri). In 2024, the Cocos Island population of the brown booby (formerly S. l. brewsteri) was elevated to full species status as the Cocos booby (Sula brewsteri), increasing the total to seven.[28] The Peruvian booby is widely recognized as distinct from the blue-footed booby, despite evidence of infrequent hybridization and asymmetrical gene flow between them in northern Peru.[90][91] Booby species display considerable morphological diversity, particularly in body size and nesting adaptations. The red-footed booby is the smallest, with adults weighing 850–1,100 g and measuring 69–79 cm in length, while the masked booby is the largest, reaching masses of 1.5–2.2 kg and lengths of 81–91 cm.[92] Nesting habits vary markedly; the red-footed booby is the only species that constructs arboreal nests in trees or shrubs using twigs, providing protection from ground predators, whereas the other species predominantly nest on the ground, cliffs, or rocky ledges.[93][7] Ecologically, boobies exploit a range of marine niches, from pelagic to coastal foraging strategies. Species like the red-footed booby and Cocos booby forage extensively in open-ocean pelagic waters, often hundreds of kilometers from colonies, while others, such as the brown and Peruvian boobies, prefer coastal and shelf-edge habitats closer to shore.[94] Certain species are island endemics, including the Cocos booby (Sula brewsteri), which breeds primarily on Cocos Island and nearby atolls in the eastern Pacific with recent range expansion westward, and Abbott's booby (Papasula abbotti), which is restricted to breeding on Christmas Island in the Indian Ocean, where it nests exclusively in tall rainforest trees.[95][96] Genetic analyses reveal low inbreeding levels across booby populations, even in isolated colonies, attributed to philopatry balanced by occasional long-distance dispersal.[97] Hybridization is rare but documented in specific cases, such as between brown and blue-footed boobies in the Gulf of California.[98] Phylogenetic studies indicate that Sula species cluster into two main clades, roughly corresponding to white-bellied forms (e.g., masked, Nazca, and red-footed boobies) and those with more extensive dark plumage on the underparts (e.g., blue-footed, Peruvian, brown, and Cocos boobies), reflecting evolutionary divergence driven by habitat specialization.[99]List of species
The boobies comprise eight recognized extant species in the genera Sula and Papasula, all within the family Sulidae. These seabirds are primarily tropical and subtropical in distribution, with key distinguishing features including plumage patterns, foot coloration, and bill shape. Below is a table summarizing the scientific name, common name, primary breeding range, population estimate, and IUCN Red List status for each species.| Scientific Name | Common Name | Breeding Range Summary | Population Estimate | IUCN Status |
|---|---|---|---|---|
| Sula sula | Red-footed booby | Pantropical oceans, on islands and atolls across the Atlantic, Pacific, and Indian Oceans (excluding eastern Atlantic). | 1.4 million mature individuals | Least Concern (LC)[71] |
| Sula nebouxii | Blue-footed booby | Eastern Pacific Ocean, along the western coast of the Americas from Mexico to northern Peru, including the Galápagos Islands. | >90,000 mature individuals | Least Concern (LC)[84] |
| Sula leucogaster | Brown booby | Pantropical, breeding on islands and coastal sites in the Atlantic, Pacific, and Indian Oceans (excluding eastern Pacific populations now recognized as Cocos booby). | 140,000–200,000 individuals (as of 2024, post-split) | Least Concern (LC)[85][31] |
| Sula dactylatra | Masked booby | Tropical and subtropical waters worldwide, breeding on oceanic islands in the Pacific, Atlantic, and western Indian Oceans (absent from eastern Atlantic and northern Indian Oceans). | Not quantified (described as fairly common) | Least Concern (LC)[76] |
| Sula granti | Nazca booby | Eastern Pacific Ocean, breeding on islands from the Galápagos (Ecuador) north to off Baja California (Mexico), including Malpelo Island (Colombia). | <50,000 individuals | Least Concern (LC)[72] |
| Sula variegata | Peruvian booby | Southeastern Pacific Ocean, along the Humboldt Current from northern Peru to central Chile. | ~1 million individuals (fluctuating with El Niño events) | Least Concern (LC)[77] |
| Sula brewsteri | Cocos booby | Eastern tropical Pacific Ocean, breeding on islands including Cocos Island (Costa Rica), Clipperton Island (France), and Malpelo Island (Colombia), with recent expansion westward. | ~130,000 individuals (roughly 65,000 breeding pairs as of 2024) | Least Concern (LC) (not separately assessed)[100] |
| Papasula abbotti | Abbott's booby | Indian Ocean, breeding exclusively on Christmas Island (Australia). | ~6,000 mature individuals | Endangered (EN)[95] |