View source for Masked booby

{{Short description|Species of bird}}
{{protection padlock|small=yes}}
{{Use dmy dates|date=June 2019}}
{{speciesbox
| status = LC
| status_system = IUCN3.1
| status_ref = <ref name="iucn status 12 November 2021">{{cite iucn |author=BirdLife International |date=2018 |title=''Sula dactylatra'' |volume=2018 |page=e.T22736173A132666363 |doi=10.2305/IUCN.UK.2018-2.RLTS.T22736173A132666363.en |access-date=12 November 2021}}</ref>
| image = Starr 080606-6808 Coronopus didymus.jpg
| image_caption = Adult, subsp. ''personata'', [[Midway Atoll]]
| image_alt = white seabird with long pale bill standing on a beach and angled part toward camera
| genus = Sula
| species = dactylatra
| authority = [[René-Primevère Lesson|Lesson]], 1831
| subdivision_ranks = Subspecies
| subdivision = See text
| range_map = Suladactylatrargemap.png
| range_map_caption = Range (in green)
}}

The '''masked booby''' ('''''Sula dactylatra'''''), also called the '''masked gannet''' or the '''blue-faced booby''', is a large [[seabird]] of the [[booby]] and [[gannet]] family, [[Sulidae]]. First described by the French naturalist [[René-Primevère Lesson]] in 1831, the masked booby is one of six species of booby in the genus ''[[Sula (bird)|Sula]]''. It has a typical sulid body shape, with a long pointed yellowish bill, long neck, aerodynamic body, long slender wings and pointed tail. The adult is bright white with black wings, a black tail and a dark face mask; at {{convert|75|-|85|cm|in|abbr=on}} long, it is the largest species of booby. The sexes have similar plumage. This species ranges across tropical oceans, except in the eastern [[Atlantic]] and eastern Pacific. In the latter, it is replaced by the [[Nazca booby]] (''Sula granti''), which was formerly regarded as a [[subspecies]] of masked booby.

Nesting takes place in [[Bird colony|colonies]], generally on islands and [[atoll]]s far from the mainland and close to deep water required for foraging. Territorial when breeding, the masked booby performs [[Agonistic behaviour|agonistic displays]] to defend its nest. Potential and mated pairs engage in courtship and greeting displays. The female lays two chalky white eggs in a shallow depression on flat ground away from vegetation. The chicks are born featherless, but are soon covered in white [[Down feather|down]]. The second chick born generally does not survive and is killed by its elder sibling. These birds are spectacular plunge [[Diving bird|divers]], plunging into the ocean at high speed in search of prey—mainly [[flying fish]]. The species faces few threats; although its population is declining, it is considered to be a [[least-concern species]] by the [[International Union for Conservation of Nature]] (IUCN).

== Taxonomy ==
The French naturalist [[René Lesson]] was a member of the crew on the ''[[French ship Astrolabe (1811)|La Coquille]]'', captained by [[Louis Isidore Duperrey]], on its voyage around the world undertaken between August 1822 and March 1825.<ref name=cretella>{{cite journal | last=Cretella | first=Massimo | year=2010 | title=The complete collation and dating of the section ''Zoologie'' of the ''Coquille'' voyage | journal=Bollettino Malacologico | volume=46 | pages=83–103 [83–84] | url=https://biodiversitylibrary.org/page/51117488 | access-date=30 May 2019 | archive-date=30 May 2019 | archive-url=https://web.archive.org/web/20190530155919/https://www.biodiversitylibrary.org/page/51117488 | url-status=live }}</ref> In the multi-volume publication by Duperrey about the voyage, Lesson authored the ornithological sections. In his 1829 account of the visit to [[Ascension Island]] in the [[South Atlantic Ocean]], Lesson mentioned encountering masked boobies, and in a footnote proposed the [[binomial name]] ''Sula dactylatra''.<ref>{{cite book |last=Lesson |first=René |author-link=René Lesson |editor=Duperrey, Louis Isidore |year=1829 |title=Voyage autour du Monde, Exécuté par Ordre du Roi, Sur la Corvette de Sa Majesté, ''La Coquille'', pendant les années 1822, 1823, 1824 et 1825 |language=fr |location=Paris |publisher=Arthus Bertrand |volume=1, Part 2 |page=494 |url=https://biodiversitylibrary.org/page/38661432 |access-date=4 March 2018 |archive-date=10 October 2018 |archive-url=https://web.archive.org/web/20181010055829/https://www.biodiversitylibrary.org/page/38661432 |url-status=live }} The title page gives the year as 1828 but the ''livraison'' containing page 494 was published in 1829 (See Cretella, 2010)</ref> Lesson subsequently provided a [[species description|formal description]] of the masked booby in 1831.<ref>{{cite book | last=Lesson | first=René | author-link=René Lesson | year=1831 | title=Traité d'Ornithologie, ou Tableau Méthodique | language=fr | place=Paris | publisher=F.G. Levrault | page=601 | url=https://biodiversitylibrary.org/page/35997585 | access-date=30 May 2019 | archive-date=30 May 2019 | archive-url=https://web.archive.org/web/20190530155909/https://www.biodiversitylibrary.org/page/35997585 | url-status=live }}</ref> The [[specific epithet]] combines the [[Ancient Greek]] {{lang|grc|δάκτυλος}} ({{Transliteration|grc|dáktul}}), meaning {{gloss|finger}}, and the Latin {{lang|la|ater}}, meaning {{gloss|black}}. "Black fingers" refers to the splayed wingtips in flight.<ref name="fraser13">{{cite book |last1=Gray |first1=Jeannie |last2=Fraser |first2=Ian |title=Australian Bird Names: A Complete Guide |url=https://books.google.com/books?id=W1TCqHVWQp0C&pg=PT151 |year=2013 |publisher=Csiro Publishing |location=Collingwood, Victoria |isbn=978-0-643-10471-6 |page=151 |access-date=6 June 2020 |archive-date=30 October 2023 |archive-url=https://web.archive.org/web/20231030204902/https://books.google.com/books?id=W1TCqHVWQp0C&pg=PT151#v=onepage&q&f=false |url-status=live }}</ref> The Swedish zoologist [[Carl Jakob Sundevall]] described the species as ''Dysporus cyanops'' in 1837<ref>{{cite journal | title=''Dysporus cyanops'' | last= Sundevall | first = Carl Jakob | journal=Physiographiska Sällskapets Tidskrift | volume= I | issue= 3| page= 218 [footnote] | year= 1838 | url= https://archive.org/details/physiographiskas00phys/page/218 | language=sv}}</ref> from a [[subadult]] collected in the Atlantic Ocean on 6{{nbsp}}September 1827.<ref>{{cite web |last1=Johanson |first1=Kjell Arne |title=NRM 569854 Dysporus cyanops Sundevall, 1838 |url=http://www.nrm.se/forskningochsamlingar/zoologi/samlingar/vertebrater/typsamlingfaglar/icketattingar/sulidae/nrm569854.3441.html |website=Maturhistoriska riksmuseet |access-date=3 March 2019 |language=sv |archive-date=6 March 2019 |archive-url=https://web.archive.org/web/20190306042642/http://www.nrm.se/forskningochsamlingar/zoologi/samlingar/vertebrater/typsamlingfaglar/icketattingar/sulidae/nrm569854.3441.html |url-status=live }}</ref> The species name was derived from the Ancient Greek words {{lang|grc|κύανος}} ({{Transliteration|grc|kúanos}}), meaning {{gloss|blue}},{{sfn|Liddell|Scott|1980|p=397}} and {{lang|grc|ὄψ}} ({{Transliteration|grc|óps}}), meaning {{gloss|face}}.{{sfn|Liddell|Scott|1980|p=804}}

The English ornithologist and bird artist [[John Gould]] described ''Sula personata'' in 1846 from Australia,<ref name="Gould">{{cite journal |author=Gould, John |author-link=John Gould |year=1846 |url=https://biodiversitylibrary.org/page/12862671 |title=Descriptions of eleven new species of Australian birds |journal=Proceedings of the Zoological Society of London |volume=14 |pages=18–21 |doi=10.1111/j.1469-7998.1846.tb00135.x |access-date=4 March 2018 |archive-date=5 December 2018 |archive-url=https://web.archive.org/web/20181205103233/https://www.biodiversitylibrary.org/page/12862671 |url-status=live }}</ref> the species name being the Latin adjective {{lang|la|personata}}, meaning {{gloss|masked}}.<ref>{{cite book |last=Simpson |first=D.P. |title=Cassell's Latin Dictionary |publisher=Cassell Ltd. |year=1979 |edition=5th |location=London |page=442 |isbn=978-0-304-52257-6}}</ref> Gould adopted the name ''Sula cyanops'' in his 1865 ''[[Handbook to the Birds of Australia]]''.<ref>{{cite book | last=Gould | first=John | author-link=John Gould | year=1865 | title=Handbook to the Birds of Australia | publisher=self-published | place=London | volume=2 | pages=506–507 | url=https://biodiversitylibrary.org/page/13966531 | access-date=29 May 2019 | archive-date=29 May 2019 | archive-url=https://web.archive.org/web/20190529141812/https://www.biodiversitylibrary.org/page/13966531 | url-status=live }}</ref> Sundevall's binomial name was followed as Lesson's 1829 record did not sufficiently describe the species; however, in 1911, the Australian amateur ornithologist [[Gregory Mathews]] pointed out that although Lesson's 1829 account did not describe the bird, his 1831 account did, and thus predated Sundevall by six years, and hence ''Sula dactylactra'' had [[Principle of Priority|priority]].<ref>{{cite journal |url=https://biodiversitylibrary.org/page/3109633 |journal=Novitates Zoologicae |year=1911 |volume=18 |pages=9–10 |title=On some necessary alterations in the nomenclature of birds |first=Gregory |last=Mathews |doi=10.5962/bhl.part.1688 |access-date=4 March 2018 |archive-date=5 December 2018 |archive-url=https://web.archive.org/web/20181205145730/https://www.biodiversitylibrary.org/page/3109633 |url-status=live |doi-access=free }}</ref> The [[American Ornithological Society|American Ornithological Union]] followed in the 17th supplement to their checklist in 1920.<ref>{{cite journal |url=https://sora.unm.edu/sites/default/files/journals/auk/v037n03/p0439-p0449.pdf |title=Seventeenth supplement to the American Ornithologists' Union check-list of North American Birds |journal=Auk |year=1920 |volume=37 |issue=3 |pages=439–449 |doi=10.2307/4073271 |jstor=4073271 |access-date=4 March 2018 |archive-date=22 October 2021 |archive-url=https://web.archive.org/web/20211022055447/https://sora.unm.edu/sites/default/files/journals/auk/v037n03/p0439-p0449.pdf |url-status=live }}</ref>

[[File:Masked Booby, Grand Turk, TC.jpg|thumb|right|Subsp. ''dactylatra'' In flight, [[Grand Turk Island]]|alt=predominantly white underside of bird in flight]]
"Masked booby" has been designated the official [[common name]] by the [[International Ornithologists' Union]] (IOC).<ref name="ioclist">{{cite web |editor1-last=Gill |editor1-first=Frank |editor1-link=Frank Gill (ornithologist) |editor2-last=Donsker |editor2-first=David |year=2017 |title=Hamerkop, Shoebill, pelicans, boobies, cormorants |work=World Bird List Version 7.1 |url=http://www.worldbirdnames.org/bow/pelicans/ |publisher=International Ornithologists' Union |access-date=31 January 2018 |archive-date=12 June 2018 |archive-url=https://web.archive.org/web/20180612141518/http://www.worldbirdnames.org/bow/pelicans/ |url-status=live }}</ref> The species has also been called the masked gannet, blue-faced booby, white booby (for its plumage), and whistling booby (for its distinctive call).<ref name="fraser13" /> The Australian ornithologist Doug Dorward promoted the name "white booby" as he felt the blue coloration of its face was less prominent than that of the [[red-footed booby]] (''Sula sula'').{{sfn|Dorward|1962|p=174}}

The masked booby is one of six species of booby in the genus ''[[Sula (bird)|Sula]]''.<ref name="ioclist" /> A 2011 genetic study (''depicted below'') using both [[Nuclear DNA|nuclear]] and [[mitochondrial DNA]] showed the masked and [[Nazca booby|Nazca boobies]] (''Sula granti'') to be each other's closest relatives, their lineage diverging from a line that gave rise to the [[blue-footed booby|blue-footed]] (''Sula nebouxii'') and [[Peruvian booby|Peruvian boobies]] (''Sula variegata''). The masked and Nazca boobies were divergent enough to indicate that the latter, formerly regarded as a [[subspecies]] of the former, should be classified as a separate species. Molecular evidence suggests they most likely diverged between 0.8 and 1.1&nbsp;million years ago. Complex water currents in the eastern Pacific may have established an environmental barrier leading to [[speciation]].<ref>{{cite journal |last1=Patterson |first1=S.A. |last2=Morris-Pocock |first2=J.A. |last3=Friesen |first3=V.L |year=2011 |title=A multilocus phylogeny of the Sulidae (Aves: Pelecaniformes) |journal=Molecular Phylogenetics and Evolution |volume=58 |issue=2 |pages=181–191 |doi=10.1016/j.ympev.2010.11.021 |pmid=21144905 |bibcode=2011MolPE..58..181P }}</ref> Subfossil bones 14,000 years old belonging to the species have been found in deposits on [[Saint Helena|St. Helena]] Island.<ref>{{cite book|url=https://archive.org/details/paleornithology23olso|title=Paleornithology of St. Helena Island, South Atlantic Ocean. Smithsonian contributions to paleobiology.Number 23.|author=Olson, Storrs L.|publisher=Smithsonian Institution|year=1975|page=[https://archive.org/details/paleornithology23olso/page/24 24]}}</ref><!-- cites para -->

{{clade| style=font-size:100%; line-height:100%
   |1={{clade
      |1=[[Red-footed booby]] (''Sula sula'')
      |2={{clade
         |1=[[Brown booby]] (''Sula leucogaster'')
         |2={{clade
            |1={{clade
               |1=Masked booby (''Sula dactylatra'')
               |2=[[Nazca booby]] (''Sula granti'')
               }}
            |2={{clade
               |1=[[Blue-footed booby]] (''Sula nebouxii'')
               |2=[[Peruvian booby]] (''Sula variegata'')
               }}
            }}
         }}
      }}
   }}

===Intraspecific variation and subspecies===
There is a [[Cline (biology)|clinal]] change in size across the masked booby's range. Birds in the Atlantic are the smallest, with the size increasing westwards though the Pacific to the Indian Ocean, where the largest individuals are found.<ref name="hbw">{{cite web |last1=Orta |first1=J. |last2=Jutglar |first2=F. |last3=Garcia |first3=E.F.J. |last4=Kirwan |first4=G.M. |last5=Boesman |first5=P. |editor1-last=del Hoyo |editor1-first=Josep |editor2-last=Elliott |editor2-first=Andrew |editor3-last=Sargatal |editor3-first=Jordi |editor4-last=Christie |editor4-first=David A. |editor5-last=de Juana |editor5-first=Eduardo |year=2017 |title=Masked booby (''Sula dactylatra'') |work=Handbook of the Birds of the World Alive |publisher=Lynx Edicions |url=https://www.hbw.com/species/masked-booby-sula-dactylatra |location=Barcelona, Spain |access-date=2 March 2019 |url-access=subscription |archive-date=30 October 2023 |archive-url=https://web.archive.org/web/20231030204906/https://birdsoftheworld.org/bow/species/masboo/cur/introduction |url-status=live }}</ref> Genetic analysis using [[mtDNA control region]] sequences shows that populations in the Indian and Pacific Oceans greatly expanded around 180,000 years ago, and that these became separated from Atlantic populations around 115,000 years ago. Furthermore, within each ocean, there is evidence of reduced [[gene flow]] between populations that does not correspond with any physical barrier.<ref name=steeves05>{{cite journal |last1=Steeves |first1=Tammy E. |last2=Anderson | first2=David J. | last3=Friesen | first3=Vicki L. |title=A role for nonphysical barriers to gene flow in the diversification of a highly vagile seabird, the masked booby (''Sula dactylatra'') |journal=Molecular Ecology |date=2005 |volume=14 |issue=12 |pages=3877–3887 |doi=10.1111/j.1365-294X.2005.02713.x |pmid=16202102 |bibcode=2005MolEc..14.3877S |s2cid=25708378 |url=https://www.researchgate.net/publication/7563338}}</ref>

Four subspecies are recognized by the International Ornithologists' Union.<ref name="ioclist" />
[[File:Suladactfam3.jpg|thumb|right|A breeding pair of subsp. ''tasmani'' and their chick, [[Norfolk Island]]| alt=Two white birds and a fluffy white chick in long grass with sea in background]]
* ''S. d. dactylatra'' <small>Lesson, 1831</small>
:Breeds in the [[Caribbean]] and some Atlantic islands including [[Ascension Island]]. There is significant genetic divergence between birds on [[Boatswain Bird Island]] off Ascension and those from [[Monito Island]] off Puerto Rico.<ref name=steeves05/>
* ''S. d. melanops'' <small>Hartlaub, 1859</small>
:Breeds in the western Indian Ocean.<ref name="Redman Stevenson Fanshawe 2016">{{cite book |last1=Redman |first1=Nigel |last2=Stevenson |first2=Terry |last3=Fanshawe |first3=John |title=Birds of the Horn of Africa: Ethiopia, Eritrea, Djibouti, Somalia, and Socotra – Revised and Expanded Edition |series=Princeton Field Guides |publisher=Princeton University Press |location=Princeton, New Jersey |year=2016 |isbn=978-0-691-17289-7 |url=https://books.google.com/books?id=QOs9DwAAQBAJ&pg=PA44 |page=44 |access-date=4 December 2018 |archive-date=7 February 2023 |archive-url=https://web.archive.org/web/20230207205623/https://books.google.com/books?id=QOs9DwAAQBAJ&pg=PA44 |url-status=live }}</ref> The German ornithologist [[Gustav Hartlaub]] described this [[taxon]] in 1859 from [[Maydh Island]] off the coast of Somalia near the [[Maydh|town of the same name]]. He noted its black mask and blue-grey feet to be distinct from Sundevall's ''cyanops'' with a blue face, and Lesson's ''dactylatra'' with yellow feet.<ref>{{cite journal |journal=The Ibis |year=1859 |volume=1 |issue=4 |url=https://biodiversitylibrary.org/page/8610835 |pages=337–352 [351–352] |last=Hartlaub |first=G. |title=List of birds observed and collected during a voyage in the Red Sea |access-date=6 March 2018 |archive-date=5 December 2018 |archive-url=https://web.archive.org/web/20181205145735/https://www.biodiversitylibrary.org/page/8610835 |url-status=live }}</ref> The subspecies name is derived from the Ancient Greek words {{lang|grc|μέλανος}} ({{Transliteration|grc|mélanos}}), meaning {{gloss|black}},{{sfn|Liddell|Scott|1980|p=431}} and {{lang|grc|ὄψ}} ({{Transliteration|grc|óps}}), meaning {{gloss|face}}.
* ''S. d. tasmani'' <small>van Tets, Meredith, Fullagar & Davidson, 1988</small> (includes ''S.&nbsp;d.&nbsp;fullagari'' as a [[junior synonym]]): Tasman booby
:The form breeding on [[Lord Howe Island|Lord Howe]] and the [[Kermadec Islands]]. The New Zealand naturalist [[Walter Oliver]] had noted that this bird had dark brown rather than pale irises in 1930, but it was not until 1990 that it was formally investigated by R. M. O'Brien and J. Davies and found to also have longer wings than other populations. They classified it as a new subspecies: ''S.&nbsp;d.&nbsp;fullagari''.<ref>{{cite journal |last1=O'Brien |first1=R.M. |first2=J. |last2=Davies |title=A new subspecies of Masked Booby ''Sula dactylatra'' from Lord Howe, Norfolk and Kermadec Islands |url=http://marineornithology.org/PDF/18/MO_1990_01.pdf |journal=Marine Ornithology |year=1990 |volume=18 |issue=1 |pages=1–7 |access-date=5 March 2018 |archive-date=27 April 2018 |archive-url=https://web.archive.org/web/20180427073338/http://www.marineornithology.org/PDF/18/MO_1990_01.pdf |url-status=live }}</ref> Meanwhile, large prehistoric specimens known from the Lord Howe and [[Norfolk Island]] had been classified as a separate species, ''S. tasmani'', in 1988, thought to have become extinct due to Polynesian and then European seafarers and settlers.<ref name=vantets88>{{cite journal |last1=van Tets |first1=G.F. |last2=Meredith |first2=C.W. |last3=Fullagar |first3=P.J. |last4=Davidson |first4=P.M. |year=1988 |title=Osteological differences between ''Sula'' and ''Morus'', and a description of an extinct new species of ''Sula'' from Lord Howe and Norfolk Islands, Tasman Sea |journal=Notornis |volume=35 |pages=35–57 [53] |url=https://notornis.osnz.org.nz/system/files/Notornis_35_1.pdf |access-date=3 March 2018 |archive-date=17 February 2021 |archive-url=https://web.archive.org/web/20210217201243/https://www.notornis.osnz.org.nz/system/files/Notornis_35_1.pdf |url-status=dead }}</ref> However, the paleoecologist Richard Holdaway and colleagues cast doubt on the distinctness of the fossil taxon in 2001,<ref>{{cite journal | title=Avifauna from the Emily Bay settlement site, Norfolk Island: a preliminary account |journal=Records of the Australian Museum Supplement |volume=27 |year=2001 |pages=85–100 |last1=Holdaway |first1=Richard |last2=Anderson |first2=Atholl |author2-link=Atholl Anderson |doi=10.3853/j.0812-7387.27.2001.1343 | doi-access=free }}</ref> and a 2010 review by the New Zealand biologist Tammy Steeves and colleagues of the fossil material and DNA found the two overlapped considerably, and hence the extinct and living entities were found to be the same taxon, now known as ''S.&nbsp;d.&nbsp;tasmani'' as this name has priority over ''S.&nbsp;d.&nbsp;fullagari''.<ref>{{cite journal |title=Merging ancient and modern DNA: extinct seabird taxon rediscovered in the North Tasman Sea |first1=Tammy E. |last1=Steeves |first2=Richard N. |last2=Holdaway |first3=Marie L. |last3=Hale |first4=Emma |last4=McLay |first5=Ian A. W. |last5=McAllan |first6=Margaret |last6=Christian |first7=Mark E. |last7=Hauber |first8=Michael |last8=Bunce |doi=10.1098/rsbl.2009.0478 |pmid=19675005 |journal=Biology Letters |volume=6 |issue=1 |pages=94–97 |year=2010 |pmc=2817237}}</ref> Fieldwork in the Kermadec Islands indicates the bills of adults are bright yellow, and that adult males had brighter yellow feet than females.<ref name=ismar>{{cite journal |title=Morphology of the recently re-classified Tasman Masked Booby ''Sula dactylatra tasmani'' breeding on the Kermadec Islands |journal=Marine Ornithology |volume=38 |issue=2 |pages=105–109 |year=2010 |url=http://eprints.uni-kiel.de/19516/1/38_2_105-109.pdf |first1=Stefanie M. H. |last1=Ismar |first2=Karen |last2=Baird |first3=Selina |last3=Patel |first4=Craig D. |last4=Millar |first5=Mark E. |last5=Hauber |access-date=22 July 2018 |archive-date=22 July 2018 |archive-url=https://web.archive.org/web/20180722095717/http://eprints.uni-kiel.de/19516/1/38_2_105-109.pdf |url-status=dead }}</ref>
* ''S. d. personata'' <small>Gould, 1846</small> (includes ''S.&nbsp;d.&nbsp;californica'' and ''S.&nbsp;d.&nbsp;bedouti'')
:Breeds in the central and western Pacific and around Australia, as well as off Mexico and on [[Clipperton Island]] in the Pacific Ocean off the coast of Central America. Birds of the latter two locations have been separated as subspecies ''californica'', and the north west Australian population has been named as subspecies ''bedouti'', but neither is usually considered distinct;<ref name="ioclist" /> the American biologist Robert Pitman and colleagues found no consistent differences between these three subspecies.<ref name=pitman1998>{{Cite journal|last1=Pitman|first1=Robert L.|last2=Jehl|first2=Joseph R. Jnr.|year=1998|title=Geographic variation and reassessment of species limits in the "Masked" Boobies of the Eastern Pacific Ocean|jstor=4163925|journal=The Wilson Bulletin|volume=110|issue=2|pages=155–170|url=https://sora.unm.edu/sites/default/files/journals/wilson/v110n02/p0155-p0170.pdf|access-date=28 May 2019|archive-date=26 January 2021|archive-url=https://web.archive.org/web/20210126215607/https://sora.unm.edu/sites/default/files/journals/wilson/v110n02/p0155-p0170.pdf|url-status=live}}</ref>

== Description ==
[[File:Kure Masked Booby juveniles.jpg|thumb|left|Juveniles of subsp ''personata'' on [[Kure Atoll]] in the [[Hawaiian Islands|Hawaiian island]] chain| alt= Seven brownish birds sitting on a large log on a beach]]
The largest species of booby, the masked booby ranges from {{convert|75|to|85|cm|in|abbr=on}} long, with a {{convert|160|-|170|cm|in|abbr=on}} wingspan and {{convert|1.2|-|2.2|kg|lb|abbr=on}} weight. It has a typical [[sulidae|sulid]] body shape, with a long pointed bill, long neck, aerodynamic body, long slender wings and pointed tail. The adult is bright white with dark wings and a dark tail.{{sfn|Marchant|Higgins|1990|p=763}}<!-- cites 3 previous sentences--> The sexes have similar plumage with no seasonal variation, but females are on average slightly heavier and larger than males.{{sfn|Marchant|Higgins|1990|pp=763, 771–772}}<!--p.763 for similar plumage, p.771 for size, p.772 for weights--> The bare skin around the face, throat and [[Lore (anatomy)|lores]] is described either as black or blue-black. It contrasts with the white plumage and gives a mask-like appearance.{{sfn|Marchant|Higgins|1990|pp=763, 771}} The bill of the [[nominate subspecies]] is pale yellow with a greenish tinge, sometimes greyish at the base.<ref name="hbw"/> Conical in shape, the bill is longer than the head and tapers to a slightly downcurved tip. Backward-pointing [[serration]]s line the mandibles.{{sfn|Marchant|Higgins|1990|p=772}} The [[Flight feather#Primaries|primaries]], [[Flight feather#Secondaries|secondaries]], [[Flight feather#Tertials|humerals]] and [[Flight feather#Rectrices|rectrices]] are brown-black. The inner webs of the secondaries are white at the base. The underwing is white except for the brown-black flight-feathers that are not covered by the white [[Flight feather#Tectrices|coverts]].{{sfn|Marchant|Higgins|1990|p=770}} The legs are yellow-orange or olive.<ref name="hbw"/> The iris is yellow.{{sfn|Marchant|Higgins|1990|p=771}}

The subspecies differ slightly in size and sometimes also in the colour of the irises, bill, legs and feet. The race ''melanops'' has an orange-yellow bill and olive-grey legs, the race ''tasmani'' has dark brown irises and dark grey-green legs and the race ''personata'' has olive to blueish-grey legs.<ref name="hbw"/> For the subspecies ''tasmani'' and the nominate ''dactylatra'', during the breeding season, the leg colour of male birds contains more yellow-red than those of the females.<ref name=ismar/><ref>{{ cite journal | last1=Rull | first1=I.L. | last2=Nicolás | first2=L. | last3=Neri-Vera | first3=N. | last4=Argáez | first4=V. | last5=Martínez | first5=M. | last6=Torres | first6=R. | year=2016 | title=Assortative mating by multiple skin color traits in a seabird with cryptic sexual dichromatism | journal=Journal of Ornithology | volume=157 | issue=4 | pages=1049–1062 | doi=10.1007/s10336-016-1352-4 | bibcode=2016JOrni.157.1049R | s2cid=11376276 }}</ref>

The juvenile is a streaked or mottled grey-brown on the head and upperparts, with a whitish neck collar. The wings are dark brown and underparts are white. Its bill is yellowish, face is blue-grey and iris a dark brown. Older immature birds have a broader white collar and rump,{{sfn|Marchant|Higgins|1990|p=763}} and more and more white feathers on the head until the head is wholly white by 14 to 15 months of age. Full adult plumage is acquired three to four months before the bird turns three years old.{{sfn|Marchant|Higgins|1990|p=771}}<!-- cites 2 previous sentences-->

The masked booby is usually silent at sea, but is noisy at the nesting colonies. The main call of male birds is a descending whistle; that of females is a loud honk.{{sfn|Marchant|Higgins|1990|p=769}}

The adult masked booby is distinguished from the related Nazca booby by its yellow rather than orange bill, larger size and less distinctive sexual dimorphism. The latter nests on steep cliffs rather than flat ground.<ref name=pitman1998/> The white [[morph (zoology)|morph]] of the red-footed booby is similar but smaller.<ref name="hbw"/> [[Abbott's booby]] (''Papasula abbotti'') has a more wholly black upperwing, and a longer neck and tail and larger head, while the [[Cape gannet]] (''Morus capensis'') and the [[Australasian gannet]] (''Morus serrator'') have a buff-yellow crown, shorter tail, white {{Birdgloss|tertiaries|humerals}} and a grey rather than yellowish bill. The juvenile masked booby resembles the [[brown booby]] (''Sula leucogaster''), though adults of that species have clearly demarcated brown and white plumage.{{sfn|Marchant|Higgins|1990|p=763}}

== Distribution and habitat ==
The masked booby is found across tropical oceans between the [[30th parallel north]] and [[30th parallel south]]. In the Indian Ocean it ranges from the coastlines of the Arabian Peninsula and East Africa across to Sumatra and Western Australia, though it is not found off the coast of the Indian subcontinent. Off the Western Australian coastline it is found as far south as the [[Dampier Archipelago]]. In the Pacific, it ranges from Brisbane eastwards. It is found in the Caribbean and Atlantic Ocean south to Ascension Island.{{sfn|Marchant|Higgins|1990|p=764}}<!-- cites para --> In the eastern Pacific off the coast of Colombia and Ecuador, the masked booby is replaced by the Nazca booby.<ref name=pitman1998/> A [[Vagrancy (biology)|vagrant]] was rescued in 2015 in [[Newport, Oregon]].<ref>{{cite web |title=Rare Tropical Booby fills up on Northwest Seafood, Catches Flight South |url=https://aquarium.org/tag/masked-booby/ |publisher=Oregon Coast Aquarium |date=7 October 2015 |access-date=1 June 2019 |archive-date=1 June 2019 |archive-url=https://web.archive.org/web/20190601211908/https://aquarium.org/tag/masked-booby/ |url-status=live }}</ref>

In the Atlantic, Caribbean birds occasionally wander north to warm southern [[Gulf Stream]] waters off the eastern seaboard of the United States, with single records from [[Island Beach State Park|Island Beach]] in New Jersey and New York.<ref>{{cite book |last1=Boyle |first1=William J. Jr. |title=The Birds of New Jersey: Status and Distribution |date=2011 |publisher=Princeton University Press |location=Princeton, New Jersey |isbn=978-1-4008-3828-8 |page=51 |url=https://books.google.com/books?id=5ejUSy8sn5cC&pg=PA51 |access-date=6 June 2020 |archive-date=30 October 2023 |archive-url=https://web.archive.org/web/20231030204906/https://books.google.com/books?id=5ejUSy8sn5cC&pg=PA51#v=onepage&q&f=false |url-status=live }}</ref> There are summer records from [[Delaware Bay]],<ref>{{cite book |last1=Brady |first1=Alan |title=Atlantic Seabird Photo Journal: Off New York, New Jersey, Delaware and Maryland Coasts to Canyons 1967–2006 |date=2009 |publisher=Xlibris Corporation |location=Bloomington IN |isbn=978-1-4500-8159-7 |pages=75–76 |url=https://books.google.com/books?id=MPDwZPQtD-8C&pg=PA75 |access-date=6 June 2020 |archive-date=30 October 2023 |archive-url=https://web.archive.org/web/20231030204906/https://books.google.com/books?id=MPDwZPQtD-8C&pg=PA75#v=onepage&q&f=false |url-status=live }}</ref> and [[Worcester County, Maryland]],<ref>{{cite book |last1=Beehler |first1=Bruce M. |title=Birds of Maryland, Delaware, and the District of Columbia |date=2019 |publisher=JHU Press |location=Baltimore, Maryland |isbn=978-1-4214-2733-1 |page=365 |url=https://books.google.com/books?id=odWLDwAAQBAJ&pg=PA365 |access-date=6 June 2020 |archive-date=30 October 2023 |archive-url=https://web.archive.org/web/20231030204908/https://books.google.com/books?id=odWLDwAAQBAJ&pg=PA365#v=onepage&q&f=false |url-status=live }}</ref> as well as waters off the coast of Spain.<ref name=Peterson1967>{{Cite book |last1=Peterson |first1=Roger Tory |last2=Mountfort |first2=Guy |last3=Hollom |first3=P.A.S. |year=2001 |orig-year=1967 |title=A Field Guide to the Birds of Britain and Europe |page=241 |url=https://books.google.com/books?id=s12BdfjtWtsC&pg=PA241 |publisher=Houghton Mifflin Harcourt |location=New York |isbn=978-0-618-16675-6 |access-date=6 June 2020 |archive-date=30 October 2023 |archive-url=https://web.archive.org/web/20231030205410/https://books.google.com/books?id=s12BdfjtWtsC&pg=PA241#v=onepage&q&f=false |url-status=live }}</ref>

During the monsoon season (midyear), the masked booby is an occasional vagrant along the western coast of India, with records from [[Kerala]], Karnataka,<ref>{{cite journal|author=Madhyastha, N.A.|year=1987|title=First report of masked booby ''Sula dactylara'' from the shores of coastal Karnataka|url=https://biodiversitylibrary.org/page/49081508|journal=Journal of the Bombay Natural History Society|volume=84|page=434|access-date=13 June 2019|archive-date=28 March 2021|archive-url=https://web.archive.org/web/20210328130706/https://www.biodiversitylibrary.org/page/49081508|url-status=live}}</ref> and [[Maharashtra]] states.<ref>{{cite journal |title=Recent records of masked booby (''Sula dactylatra'') along the western coast of India |first=Raju |last=Kasambe |journal=Newsletter for Birdwatchers |pages=59–60 |volume=50 |issue=4 |year=2010 | url=https://www.researchgate.net/publication/265652060 }}</ref> It is a vagrant to the [[Caroline Islands]] north of New Guinea.<ref>{{cite journal |last1=Wiles |first1=G.J. |first2=D.J. |last2=Worthington |first3=R.E. |last3=Beck, Jr. |first4=H.D. |last4=Pratt |first5=C.F. |last5=Aguon |first6=R.L. |last6=Pyle |year=2000 |title=Noteworthy bird records for Micronesia, with a summary of raptor sightings in the Mariana Islands, 1988–1999 |journal=Micronesica |volume=32 |issue=2 |pages=257–284 [260] |url=http://micronesica.org/sites/default/files/16_wiles_etal.pdf |access-date=26 April 2018 |archive-date=22 April 2018 |archive-url=https://web.archive.org/web/20180422033603/http://micronesica.org/sites/default/files/16_wiles_etal.pdf |url-status=live }}</ref>

=== Breeding colonies ===
[[File:Starr 060228-6311 Chenopodium oahuense.jpg|thumb|right|Breeding sites in areas relatively free of vegetation, Oahu| alt=Birds nesting across a flat rocky area near the sea]]
Breeding colonies are located on remote islands, atolls and cays.{{sfn|Marchant|Higgins|1990|p=763}} Lord Howe Island is the southernmost colony.{{sfn|Marchant|Higgins|1990|p=764}} Deep water nearby is important for feeding. As an example, waters around [[Raine Island]], at the edge of the [[Great Barrier Reef]], are anywhere from {{convert|180|to|3700|m|ft|abbr=on}} deep.{{sfn|Marchant|Higgins|1990|p=763}} On these landforms, masked boobies select sites of generally flat, bare or exposed open ground that lie above the high-tide level with access to the ocean.{{sfn|Marchant|Higgins|1990|p=764}} During the breeding season, the species remains near the colony. At other times, juveniles and some adults disperse widely, though some remain at the colony year-round. Most (but not all) birds return to breed at the colony of their birth; once they begin breeding at a site, they will return there annually.{{sfn|Marchant|Higgins|1990|p=763}}<!-- cites previous 3 sentences-->

The largest masked booby colony is on Clipperton Island in the eastern Pacific Ocean,<ref name="hbw"/> a desert atoll southwest of Mexico. In 2003, 112,000 birds were counted, having recovered from 150 individuals in 1958. The population had suffered from the introduction of [[feral pigs]] in the 1890s. These pigs preyed on the crabs that ate the vegetation. After the elimination of pigs in 1964, the crab population rose and vegetation largely disappeared. This was beneficial to the boobies, as they prefer open ground.<ref name="Pitman et al. 2005">{{cite journal |last1=Pitman |first1=Robert L. |first2=Lisa T. |last2=Ballance |first3=Charly |last3=Bost |year=2005 |title=Clipperton Island: pigsty, rat hole and booby prize |journal=Marine Ornithology |url=http://mundo.cabrillo.edu/~ncrane/Clipperton/ratsandpigs.pdf |volume=33 |issue=2 |pages=193–194 |access-date=1 March 2019 |archive-date=19 November 2020 |archive-url=https://web.archive.org/web/20201119121316/http://mundo.cabrillo.edu/~ncrane/Clipperton/ratsandpigs.pdf |url-status=dead }}</ref> Clipperton is on a narrow ridge surrounded by deep water.<ref name="Weimerskirch08">{{cite journal |last1=Weimerskirch |first1=Henri |first2=Matthieu |last2=Le Corre |first3=Charles A. |last3=Bost |title=Foraging strategy of masked boobies from the largest colony in the world: relationship to environmental conditions and fisheries |journal=Marine Ecology Progress Series |date=2008 |volume=362 |pages=291–302 |doi=10.3354/meps07424 |url=https://www.int-res.com/articles/meps2008/362/m362p291.pdf |bibcode=2008MEPS..362..291W |doi-access=free |access-date=31 May 2019 |archive-date=10 August 2020 |archive-url=https://web.archive.org/web/20200810185743/https://www.int-res.com/articles/meps2008/362/m362p291.pdf |url-status=live }}</ref> The colony on Lord Howe Island numbered in the thousands at the time of the island's discovery in 1788, but has declined to under 500 pairs—mostly on offshore islets with the remainder on two hard-to-access headlands—by 2005. Hunting by humans is thought to have played a role; although rats were introduced to the island in 1918, there has been no evidence they are able to kill chicks or eggs—possibly due to the size of the adult boobies.<ref name=Priddel05>{{cite journal |last1=Priddel |first1=David |first2=Ian |last2=Hutton |first3=Samantha|last3= Olson |first4= Robert |last4=Wheeler | title=Breeding biology of Masked Boobies (''Sula dactylatra tasmani'') on Lord Howe Island, Australia |journal=Emu |date=2005 |volume=105 |issue=2 |pages=105–113 |doi=10.1071/MU04028|bibcode=2005EmuAO.105..105P |s2cid=55658891 }}</ref> The masked booby was first recorded breeding on [[Phillip Island (Norfolk Island)|Philip Island]] off Norfolk Island in 1908, with devegetation by feral animals creating the open ground preferred by the species. By 2007, an estimated 300 pairs were breeding over the island, though the island flora's regeneration after the removal of feral animals might begin to limit suitable nesting sites.<ref name=priddel10>{{cite journal |last1=Priddel |first1=David |first2=Nicholas |last2=Carlile |first3=Olwyn |last3=Evans |first4=Beryl |last4=Evans |first5=Honey |last5=McCoy |title=A review of the seabirds of Phillip Island in the Norfolk Island Group |journal=Notornis |date=2010 |volume=57 |pages=113–127 |url=http://notornis.osnz.org.nz/system/files/Priddel%20et%20al.%202010.pdf |access-date=2 June 2019 |archive-date=21 February 2021 |archive-url=https://web.archive.org/web/20210221161051/http://notornis.osnz.org.nz/system/files/Priddel%20et%20al.%202010.pdf |url-status=dead }}</ref> In 2006, two pairs nested in a brown booby colony on Morros del Potosí (White Friars Rocks) near [[Zihuatanejo]] in southern Mexico.<ref>{{cite journal |last1=Castillo-Guerrero |first1=Alfredo |first2=Juan Pablo |last2=Ceyca |first3=Eric |last3=Mellink |title=A nesting record of the Masked Booby from Guerrero, Southern Mexico |journal=Western Birds |date=2007 |volume=38 |pages=229–231 |url=https://www.researchgate.net/publication/235654578 |access-date=4 July 2019 |archive-date=28 March 2021 |archive-url=https://web.archive.org/web/20210328130840/https://www.researchgate.net/publication/235654578_A_nesting_record_of_the_Masked_Booby_from_Guerrero_Southern_Mexico |url-status=live }}</ref>

Major nesting areas in the Atlantic include [[Rocas Atoll]] off the coast of Brazil,<ref>{{cite journal | last1=Mancini | first1=P.L. | last2=Serafini | first2=P.P. | last3=Bugoni | first3=L. | year=2016 | title=Breeding seabird populations in Brazilian oceanic islands: historical review, update and a call for census standardization | journal=Revista Brasileira de Ornitologia | volume=24 | issue=2 | pages=94–115 [99] | doi=10.1007/BF03544338 | url=https://www.researchgate.net/publication/308878960 | doi-access=free | access-date=6 June 2020 | archive-date=28 March 2021 | archive-url=https://web.archive.org/web/20210328130840/https://www.researchgate.net/publication/308878960_Breeding_seabird_populations_in_Brazilian_oceanic_islands_Historical_review_update_and_a_call_for_census_standardization | url-status=live }}</ref> Ascension Island in the south Atlantic,<ref name=ratcliffe/><!--4,500 pairs--> and five islands of the [[Campeche Bank]] in the [[Gulf of Mexico]].<ref>{{ cite report | last1=Tunnell | first1=John W. | last2=Chapman | first2=Brian R.| year=2000 | title=Seabirds of the Campeche Bank Islands, southeastern Gulf of Mexico | series=Atoll Research Bulletin No. 482 | location=Washington DC | publisher=Smithsonian | hdl=10088/4870 | hdl-access=free }}<!--4,519 active nests on five of the islands--></ref><ref>{{cite journal | last1=Morales-Vera | first1=T.E. | last2=Ruz-Rosado | first2=F.D. | last3=Velarde | first3=E. | last4=Keith | first4=E.O. | year=2017 | title=Status of seabird nesting populations on Arrecife Alacranes, Gulf of Mexico | journal=Marine Ornithology | volume=45 | pages=175–185 | url=https://sora.unm.edu/sites/default/files/45_2_175-185_0.pdf | access-date=11 June 2019 | archive-date=13 April 2021 | archive-url=https://web.archive.org/web/20210413002641/https://sora.unm.edu/sites/default/files/45_2_175-185_0.pdf | url-status=live }}</ref> The species attempted to nest at [[Dry Tortugas]] in the Gulf of Mexico over 1984 and 1985;<ref>{{cite journal |last1=Clapp |first1=Roger | first2= William B. Jr | last2=Robertson |title=Nesting of the Masked Booby on the Dry Tortugas, Florida: The first record for the contiguous United States |journal=Colonial Waterbirds |date=1986 |volume=9 |issue=1 |pages=113–116 |doi=10.2307/1521152|jstor=1521152 |bibcode=1986ColWa...9..113C }}</ref> 19 pairs were recorded there in 1998.<ref>{{cite web |title=Dry Tortugas National Park |url=https://www.audubon.org/important-bird-areas/dry-tortugas-national-park |publisher=National Audubon Society |access-date=1 June 2019 |date=2016-09-12 |archive-date=8 February 2022 |archive-url=https://web.archive.org/web/20220208174226/https://www.audubon.org/important-bird-areas/dry-tortugas-national-park |url-status=live }}</ref>

== Behaviour ==
{| style="float:right;"
|-
|[[File:Masked Boobies Courting (6741932765).jpg|200px|thumb|right|Subsp. ''personata'', Courting display,<br> [[French Frigate Shoals]]|alt=Two white birds touching bills.]]
|-
|[[File:Sula dactylatra MHNT.ZOO.2010.11.45.6.jpg|200px|thumb|right|Egg|alt=Whitish egg on black background]]
|-
|[[File:Masked Booby Chicken.jpg|200px|thumb|right|Egg and chick of subsp. ''dactylatra'' in nest, [[Ascension Island]]|alt=Tiny naked chick nestled in feet of larger parent bird.]]
|}
The masked booby generally flies at least {{convert|7|m|ft|abbr=on}} in height, and at speeds of up to {{convert|70|km/h|mph|abbr=on}}. It alternates between gliding and active flying with strong periodic wingbeats. It is often encountered alone, or in a small group when returning to its colony.{{sfn|Marchant|Higgins|1990|p=763}}<!-- cites 2 preceding sentences -->

Regarding the masked booby's longevity, a bird tagged at [[Nepean Island (Norfolk Island)|Nepean Island]] (off Norfolk Island) in September 1979 was recovered and released after being caught in fishing gear 24 years and 9.9 months later some {{cvt|713|km}} away off the [[Isle of Pines (New Caledonia)|Isle of Pines]], New Caledonia in July 2004. The longest distance travelled is {{cvt|3152|km}}; a bird tagged at Raine Island in the [[Great Barrier Reef]] in December 1981 was picked up and released at Phillip Island (off Norfolk Island) in December 1986.<ref>{{cite web|url=http://www.environment.gov.au/cgi-bin/biodiversity/abbbs/abbbs-search.pl?taxon_id=1021|title=ABBBS Database Search: Sula dactylatra (Masked booby)|last=Australian Bird & Bat Banding Scheme (ABBBS)|date=2018|work=Bird and bat banding database|publisher=Australian Government Department of the Environment and Energy|access-date=1 June 2019|archive-date=30 October 2023|archive-url=https://web.archive.org/web/20231030205417/http://www.environment.gov.au/cgi-bin/biodiversity/abbbs/abbbs-search.pl?taxon_id=1021|url-status=live}}</ref><!-- cites previous two sentences -->

===Breeding and courtship===
The masked booby begins breeding by around four or five years of age, though can occasionally do so at three years old.<ref name=florida/> Adults form [[Monogamy in animals|monogamous]] relationships with many pairs remaining together over multiple breeding seasons. Highly territorial when nesting, single males and mated pairs engage in [[Agonistic behaviour|agonistic displays]] to mark their ground against neighbours and interlopers. The male advertises his territory to females by ''flight circuiting''—making a short flight and holding his wings in a 'V' shape and making a call as he lands. The mated pair engages in ''outposting'' as other boobies fly overhead, stretching their necks out and forward. More direct trespassers are confronted with a ''yes-no headshaking'', in which the booby shakes its head from side to side or up and down and ruffles its head feathers to make its head look bigger and facial markings more prominent. It may cock its tail and hold its wings up away from its body.{{sfn|Marchant|Higgins|1990|p=767}}<!-- cites 3 preceding sentences --> Neighbouring boobies may escalate by jabbing and lunging at each other. In the ''pelican posture'', a bird tucks the tip of its bill into its chest, possibly positioned to avoid injury to others. This posture is used against intruders or as advertising for a mate.{{sfn|Marchant|Higgins|1990|p=768}}<!-- cites 2 preceding sentences -->

There are several displays related to the establishment and maintenance of pair-bonding. The male initiates ''sky-pointing'' when a female approaches or leaves his territory. In this display, he paces slowly with his neck and bill pointed upwards—between vertical and 45 degrees—with wings partly raised and whistling faintly with an open bill. In a ''gazing'' display, one bird stares at another of the opposite sex; this generally leads to other displays. Pairs engage in a (mostly) gentler form of jabbing display, and [[Preening (bird)#Allopreening|allopreening]]. In an ''oblique headshake'', a bird flings its head vigorously. The male may also parade in front of the female, walking with an exaggerated high-stepping gait and intermittently tucking his head in his breast, after collecting nesting material and before the pair begins laying. The male presents small sticks and debris as nesting material in a gesture of symbolic nest-building, which leads to copulation. Afterwards, the pair engages in more symbolic nest-building.{{sfn|Marchant|Higgins|1990|p=768}}<!-- cites para --> The twigs and debris are cleared away later as none is actually used in adorning the nest while in use.{{sfn|Marchant|Higgins|1990|p=769}}

Breeding takes place at different times of year throughout its range. On the [[Cocos (Keeling) Islands]], egg-laying takes place from January to July, peaking in June, with juvenile birds from April to December. On Moulter Cay in the [[Coral Sea]], breeding takes place year-round, with egg-laying peaking from September to early November, while on nearby Raine Island birds begin laying in or after August, likely peaking September to early November.{{sfn|Marchant|Higgins|1990|p=769}} Eggs are laid between May and September on Lord Howe Island,<ref name=Priddel05/> and early July to early January (peaking in September) on Phillip Island.<ref name=priddel10/>

In the northern hemisphere, egg-laying on [[Kure Atoll]] can be any time from January to early July, peaking in February and March.<ref name=woodward72>{{cite journal | last=Woodward | first=Paul W. | year=1972 | title=The natural history of Kure Atoll, Northwestern Hawaiian Islands | journal=Atoll Research Bulletin| volume=164 | issue=164 | pages=1–318 [148–167] | hdl=10088/6078 | doi=10.5479/si.00775630.164.1 }}</ref> On Clipperton Island, egg-laying peaks in November to coordinate with peak fish productivity of the surrounding waters in January (for growing chicks).<ref name="Weimerskirch08"/> Masked boobies lay at any time in the Caribbean, peaking between March and September.<ref name=florida>{{cite book |last1=Nellis |first1=David W. |title=Common Coastal Birds of Florida and the Caribbean |date=2001 |publisher=Pineapple Press Inc |location=Sarasota, Florida |isbn=978-1-56164-191-8 |pages=95–97 |url=https://books.google.com/books?id=-REZ4R8wBg4C&pg=PA95 |access-date=6 June 2020 |archive-date=30 October 2023 |archive-url=https://web.archive.org/web/20231030205413/https://books.google.com/books?id=-REZ4R8wBg4C&pg=PA95#v=onepage&q&f=false |url-status=live }}</ref>

The nest is a cleared area {{cvt|0.75|to|1|m}} in diameter, within which is a clearly demarcated {{cvt|25|to|30|cm|0}} shallow ({{cvt|1|-|2|cm|1}} deep) depression. A clutch of two chalky white eggs is laid, with an interval of five to eight days between the laying of each egg. Occasionally nests with three eggs are reported; these are probably due to an egg from another nest rolling downhill into the nest.{{sfn|Marchant|Higgins|1990|p=769}}<!-- cites previous 3 sentences --> The eggs have an average size of {{cvt|64|x|45|mm}} and weigh {{cvt|75|g}}.{{sfn|Marchant|Higgins|1990|p=769}} They are incubated by both adults for 45 days.<ref name=Priddel05/> Parents incubate the eggs by resting on their {{Birdgloss|tarsi}} and wrapping their webbed feet over the eggs, with the outermost toes resting on the ground. Their feet are more vascular at this time.{{sfn|Dorward|1962|pp=185–186}} When first hatched, the chicks are about {{cvt|10|cm}} long and weigh around {{cvt|40|-|60|g}}, with a sparse covering of white down over their grey to pinkish-grey skin. [[Altricial]] and [[nidicolous]], their eyes are open at birth. Their down thickens as they age, and the chicks are quite fluffy by week 5–6. The primaries and rectrices appear by week 8, and {{Birdgloss|scapulars}} appear by week 10. They begin losing their down from week 12 onwards, until they are wholly covered by juvenile plumage by week 15 or 16, and [[fledge]] at around 120 days (17 weeks) of age.{{sfn|Marchant|Higgins|1990|p=770}} After leaving the nest, young birds are dependent on their parents for 3–4 weeks before dispersing out to sea.{{sfn|Dorward|1962|p=179}}<ref>{{cite book|url=https://archive.org/details/breedingbiologyo00kepl |title=Breeding Biology of the Blue-faced Booby (Sula dactylatra personata) on Green Island, Kure Atoll|last=Kepler | first=Cameron B.|publisher=Nuttall Ornithology Club|year=1969|place=Cambridge, MA | oclc=248142 | pages=[https://archive.org/details/breedingbiologyo00kepl/page/33 33]–34 }}</ref>

Although two eggs are often laid, the younger chick almost always perishes within a few days. This has been observed widely across the species' range. Dorward suspected [[siblicide]] on Ascension Island.{{sfn|Dorward|1962|pp=194–197}} Siblicide has been observed in the Nazca booby on the [[Galapagos Islands]],<ref>{{cite journal |last1=Anderson |first1=Atholl |author1-link=Atholl Anderson |title=The role of parents in sibilicidal brood reduction of two booby species |journal=The Auk |year=1995 |volume=112 |issue=4 |pages=860–869 |doi=10.2307/4089018 |jstor=4089018 |url=https://sora.unm.edu/sites/default/files/journals/auk/v112n04/p0860-p0869.pdf |access-date=28 May 2019 |archive-date=28 May 2019 |archive-url=https://web.archive.org/web/20190528134502/https://sora.unm.edu/sites/default/files/journals/auk/v112n04/p0860-p0869.pdf |url-status=live }}</ref> and is assumed to occur in the masked booby as well.{{sfn|Dorward|1962|pp=194–197}}<ref name=Priddel05/>

=== Feeding ===
[[File:Cheilopogon melanurusPCCA20070623-3956B.jpg|thumb|left|Flying fish, such as the [[Atlantic flyingfish]], are a common prey item.]]
The masked booby is a spectacular diver, plunging vertically or near-vertically from heights of anywhere from {{convert|12|to|100|m|ft|abbr=on|round=5}}—but more commonly {{convert|15|to|35|m|ft|abbr=on|round=5}}—above the water into the ocean at high speed, to depths of up to {{convert|3|m|ft|abbr=on}} in search of fish.{{sfn|Marchant|Higgins|1990|p=765}} It generally swallows its catch underwater.{{sfn|Marchant|Higgins|1990|p=766}} Fieldwork at Clipperton Island showed that masked boobies flew on average to {{convert|103|km|mi|abbr=on}} from their colony, with a maximum range of {{convert|242|km|mi|abbr=on}}, while feeding their chicks. They did not rest at sea at night, though part of their return trip was at night time for longer expeditions.<ref name="Weimerskirch08"/> The masked booby forages with the [[white-bellied storm petrel]] (''Fregetta grallaria'') and [[Bulwer's petrel]] (''Bulweria bulwerii'') at times.<ref>{{cite journal |first1=David G. |last1=Ainley |first2=Robert J. |last2=Boekelheide |title=An ecological comparison of oceanic seabird communities of the South Pacific Ocean |journal=Studies in Avian Biology |year=1984 |volume=8 |pages=2–23 [18] |url=https://sora.unm.edu/node/139193 |access-date=6 March 2018 |archive-date=11 August 2020 |archive-url=https://web.archive.org/web/20200811193408/https://sora.unm.edu/node/139193 |url-status=live }}</ref> [[Frigatebird]]s often harass the species until they disgorge their catch and steal their food.<ref name="hbw" />

Fish, particularly [[flying fish]], up to {{convert|28|cm|in|abbr=on}} long (rarely up to {{convert|41|cm|in|abbr=on}}) form the bulk of its diet, along with [[cephalopod]]s.<ref name="hbw" /> Species eaten include various species of flying fish such as [[blue flyingfish]] (''Exocoetus volitans''), [[mirrorwing flyingfish]] (''Hirundichthys speculiger''), [[sailfin flyingfish]] (''Parexocoetus brachypterus''), [[Cheilopogon atrisignis|glider flyingfish]] (''Cheilopogon atrisignis'') and [[Atlantic flyingfish]] (''Cheilopogon melanurus''), other fish such as [[yellowtail amberjack]] (''Seriola lalandi''), [[skipjack tuna]] (''Katsuwonus pelamis''), [[mackerel scad]] (''Decapterus macarellus''), [[pompano dolphinfish]] (''Coryphaena equiselis''), [[mahi-mahi]] (''Coryphaena hippurus''), [[brown chub]] (''Kyphosus bigibbus''), [[redbarred hawkfish]] (''Cirrhitops fasciatus''), [[snake mackerel]] (''Gempylus serpens''), [[frigate tuna]] (''Auxis thazard''), [[Pacific saury]] (''Cololabis saira''), [[Euleptorhamphus viridis|ribbon halfbeak]] (''Euleptorhamphus viridis''), [[flat needlefish]] (''Ablennes hians'') and mullet of the genus ''[[Mugil]]'', and the [[Sthenoteuthis oualaniensis|purpleback flying squid]] (''Sthenoteuthis oualaniensis'').{{sfn|Marchant|Higgins|1990|p=766}}<!-- cites para -->

==Predators and parasites==
[[Silver gull]]s (''Chroicocephalus novaehollandiae'') and [[buff-banded rail]]s (''Gallirallus philippensis'') prey on eggs and young. On some islands such as Ascension and Saint Helena, feral cats have been a threat to masked boobies.<ref name=ratcliffe>{{cite journal | last1=Ratcliffe | first1=Norman | last2=Bella | first2=Mike | last3=Pelembe | first3=Tara | last4=Boyle | first4=Dave | last5=Benjamin | first5=Raymond | last6=White | first6=Richard | last7=Godley | first7=Brendan | last8=Stevenson | first8=Jim | last9=Sanders | first9=Sarah | year=2010 | title=The eradication of feral cats from Ascension Island and its subsequent recolonization by seabirds | journal=Oryx | volume=44 | issue=1 | pages=20–29 | doi=10.1017/S003060530999069X | doi-broken-date=1 November 2024 | s2cid=51902194 | url=http://www.ascension-island.gov.ac/wp-content/uploads/2012/12/Ratcliffe-et-al-2009-The-eradication-of-feral-cats-from-Ascension-Island-and-its-subsequent-recolonization-by-seabirds.pdf | doi-access=free | access-date=2 June 2019 | archive-date=2 February 2017 | archive-url=https://web.archive.org/web/20170202210602/http://www.ascension-island.gov.ac/wp-content/uploads/2012/12/Ratcliffe-et-al-2009-The-eradication-of-feral-cats-from-Ascension-Island-and-its-subsequent-recolonization-by-seabirds.pdf | url-status=live }}</ref><ref>{{cite journal | last1=Bolton | first1=M. | last2=Watt | first2=R. | last3=Fowler | first3=E. | last4=Henry | first4=L. | last5=Clingham | first5=E. | year=2011 | title=Re-colonisation and successful breeding of masked boobies ''Sula dactylatra'' on mainland St Helena, South Atlantic, in the presence of feral cats ''Felis catus'' | journal=Seabird | volume=24 | pages=60–71 | doi=10.61350/sbj.24.60 | s2cid=131226663 | url=http://www.seabirdgroup.org.uk/journals/seabird-24/seabird-24-60.pdf | access-date=2 June 2019 | archive-date=2 June 2019 | archive-url=https://web.archive.org/web/20190602122927/http://www.seabirdgroup.org.uk/journals/seabird-24/seabird-24-60.pdf | url-status=live }}</ref> The tick species ''Ornithodoros (Alectorobius) muesebecki'' was described parasitising nesting blue-faced boobies off the Arabian coast.<ref>{{cite journal|author=Hoogstraal, Harry|year=1969|title=''Ornithodoros'' (''Alectorobius'') ''muesebecki'' n. sp., a parasite of the blue-faced booby (''Sula dactylatra melanops'') on Hasikiya Island, Arabian Sea|url=https://biodiversitylibrary.org/page/16277876|journal=Proceedings of the Entomological Society of Washington|volume=71|pages=368–374|access-date=13 June 2019|archive-date=15 April 2019|archive-url=https://web.archive.org/web/20190415115833/https://www.biodiversitylibrary.org/page/16277876|url-status=live}}</ref> The [[Argasidae|argasid]] tick ''[[Ornithodoros capensis]]'' and the [[Ixodidae|ixodid]] tick ''[[Amblyomma loculosum]]'' have also been recorded as parasites, the latter possibly spreading [[Babesiosis|piroplasmosis]] caused by ''[[Babesia]]'' among boobies.<ref>{{cite journal|last1=Peirce|first1=M.A.|last2=Feare|first2=C.J.|year=1978|title=Piroplasmosis in the masked booby ''Sula dactylatra melanops'' in the Amirantes, Indian Ocean|url=https://biodiversitylibrary.org/page/40824665|journal=Bulletin of the British Ornithologists' Club|volume=98|pages=38–40|access-date=13 June 2019|archive-date=20 March 2022|archive-url=https://web.archive.org/web/20220320145054/https://www.biodiversitylibrary.org/page/40824665|url-status=live}}</ref> On Raine Island and Pandora Cay, nests have been destroyed by [[green sea turtle]]s (''Chelonia mydas'') as they pass through booby colonies and dig their own nests in large numbers.<ref>{{cite journal |last1=King |first1=B.R. |title=Seabird Islands No. 43/1 – Raine Island, Great Barrier Reef, Queensland |journal=Corella |date=1986 |volume=10 |issue=3 |pages=73–77 |url=https://absa.asn.au/wp-content/uploads/2015/01/C10373.pdf |access-date=13 June 2019 |archive-url=https://web.archive.org/web/20190415111354/https://www.absa.asn.au/wp-content/uploads/2015/01/C10373.pdf |archive-date=15 April 2019 |url-status=dead }}</ref> Rats prey on eggs and young of many seabirds, though the size of masked boobies probably prevents direct predation. On Clipperton Island, rats prey on the crab that eats vegetation.<ref name="Pitman et al. 2005"/>

== Relationship with humans ==
The [[Taíno]] ate masked and red-footed boobies that nested on [[Grand Turk Island]] around 1000 years ago. The two species subsequently vanished from the Turks and Caicos Islands. A booby yielded around 1–2&nbsp;kg (2–5&nbsp;lb) of meat. European sailors in the area also caught and ate tame boobies.<ref>{{cite book | title=Talking Taino: Caribbean Natural History from a Native Perspective | first1=William F. | last1=Keegan | first2=Lisabeth A. | last2=Carlson | page=44 | url=https://books.google.com/books?id=Qy8LESKyJS0C&pg=PA44 | publisher=University of Alabama Press | location=Tuscaloosa | year=2008 | isbn=978-0-8173-5508-1 | access-date=6 June 2020 | archive-date=30 October 2023 | archive-url=https://web.archive.org/web/20231030205414/https://books.google.com/books?id=Qy8LESKyJS0C&pg=PA44#v=onepage&q&f=false | url-status=live }}</ref> Masked booby young and eggs were eaten by the crew of {{HMS|Supply|1759|6}} on Lord Howe Island.<ref name=vantets88/>

==Conservation status==
The [[International Union for Conservation of Nature]] (IUCN) lists the masked booby as a species of [[least concern]], though the population worldwide is decreasing.<ref name="iucn status 12 November 2021" /> At Clipperton Island, the colony was benefitted by the presence of [[yellowfin tuna]] (''Thunnus albacares''), which drove their prey item—flying fish—to the surface, facilitating predation by boobies. It may be that overfishing of tuna adversely impacts the availability of fish there.<ref name="Weimerskirch08"/> In 2005, 508 young masked boobies at the colony suffered from "[[angel wing]]", a congenital deformity of one or both wings resulting in flightlessness. This coincided with a season of high nestling mortality that was likely related to low numbers of yellowfin tuna due to possible overfishing at a crucial time in the breeding season.<ref>{{cite journal |last1=Pitman |first1=Robert L. | first2= Lisa T. | last2=Ballance | first3=Charles A. | last3=Bost |title=Incidence of Wing Deformities ('Angel Wing') Among Masked Boobies at Clipperton Island: Life History Consequences and Insight into Etiology |journal=The Wilson Journal of Ornithology |date=2012 |volume=124 |issue=3 |pages=597–602 | jstor=23324568 | doi=10.1676/11-208.1|s2cid=85187886 }}</ref> The warm phase ([[El Niño]]) of the [[El Niño–Southern Oscillation]] in 1982 and 1983 negatively impacted breeding on Christmas Island as the higher water temperatures reduced food supply. Where usually 1500 pairs nested, no young were observed over this period; 50–60 pairs were observed breeding in October 1983.<ref name="Schreiber84">{{cite journal |last1=Schreiber |first1=Ralph W. |last2=Schreiber |first2=Elizabeth Anne |title=Central Pacific Seabirds and the El Niño Southern Oscillation: 1982 to 1983 Perspectives |journal=Science |date=1984 |volume=225 |issue=4663 |pages=713–716 | jstor=1693159|doi=10.1126/science.225.4663.713 |pmid=17810291 |bibcode=1984Sci...225..713S |s2cid=40459951 }}</ref> The Australian government has rated both subspecies occurring in Australian waters as [[Climate change vulnerability|vulnerable to climate change]]. The low-lying colonies of subspecies ''personata'' are at risk from rising sea levels, and the rising sea temperatures are calculated to reduce food productivity, which may impact on breeding success of both subspecies.<ref>{{cite book |last1=Garnett |first1=Stephen |first2=Donald |last2=Franklin |title=Climate Change Adaptation Plan for Australian Birds |date=2014 |publisher=Csiro Publishing |location=Collingwood, Victoria |isbn=978-0-643-10803-5 |page=111 |url=https://books.google.com/books?id=607nAwAAQBAJ&pg=PA111 |access-date=6 June 2020 |archive-date=30 October 2023 |archive-url=https://web.archive.org/web/20231030205916/https://books.google.com/books?id=607nAwAAQBAJ&pg=PA111#v=onepage&q&f=false |url-status=live }}</ref>

== References ==
{{Reflist}}

=== Cited texts ===
{{Commons category|Sula dactylatra}}
{{Wikispecies|Sula dactylatra}}
{{refbegin}}
* {{cite journal |first=Douglas Fyffe | last= Dorward |title=Comparative biology of the White Booby and the Brown Booby ''Sula'' spp. at Ascension |journal=[[Ibis (journal)|Ibis]] | volume=103B |issue=2 |pages=174–220 |date=1962 |doi=10.1111/j.1474-919X.1962.tb07244.x }}
* {{cite book |first1=Henry George |last1=Liddell |author-link=Henry Liddell |first2=Robert |last2=Scott |author-link2=Robert Scott (philologist) |year=1980 |orig-year=1871 |title=A Greek-English Lexicon |publisher=[[Oxford University Press]] |location=Oxford |isbn=978-0-19-910207-5 |title-link=A Greek-English Lexicon |edition=Abridged }}
* {{cite book |editor1-last=Marchant |editor1-first=S. |editor2-last=Higgins |editor2-first=P.G. |year=1990 |chapter=''Sula dactylatra'' Masked booby |title=Handbook of Australian, New Zealand & Antarctic Birds. Volume 1: Ratites to ducks; Part B, Australian pelican to ducks |place=Melbourne, Victoria |publisher=Oxford University Press |isbn=978-0-19-553068-1 |pages=763–772 |chapter-url=http://nzbirdsonline.org.nz/sites/all/files/127_Masked%20Booby.pdf |access-date=25 May 2019 |archive-date=7 May 2019 |archive-url=https://web.archive.org/web/20190507235327/http://nzbirdsonline.org.nz/sites/all/files/127_Masked%20Booby.pdf |url-status=live }}
{{refend}}
{{Suliformes}}

{{Taxonbar|from=Q602084}}

{{featured article}}

[[Category:Boobies|Masked booby]]
[[Category:Birds of the Caribbean]]
[[Category:Birds of Hawaii]]
[[Category:Birds of Norfolk Island]]
[[Category:Birds of the Middle East]]
[[Category:Birds of Ascension Island]]
[[Category:Birds of the Atlantic Ocean]]
[[Category:Birds of the Indian Ocean]]
[[Category:Birds of the Pacific Ocean]]
[[Category:Birds described in 1831|Masked booby]]
[[Category:Taxa named by René Lesson]]
[[Category:Fauna of the Pantropical realm]]