The Amazonian manatee (Trichechus inunguis), commonly referred to as cowfish in Brazil,[4] is a species of manatee that lives in the Amazon Basin in Brazil, Peru, Colombia and Ecuador.[2] It has thin, wrinkled brownish or gray colored skin, with fine hairs scattered over its body and a white chest patch.[5][6] It is the smallest of the three extant species of manatee.[7]
The specific name, inunguis is Latin for "nailless". The genus name Trichechus, comes from Latin meaning "hair", referencing the whiskers around the manatee's mouth.[5]
The Amazonian manatee is the smallest member of the manatee family and
can be distinguished by its smoother rubbery skin and lack of vestigial
nails on its flippers.[8]
Ranges of body weight and size observed are 7.5–346 kg (17–763 lb) and
76.0–225 cm (2 ft 5.9 in – 7 ft 4.6 in) for captive males, 8.1–379 kg
(18–836 lb) and 71.0–266 cm (2 ft 4.0 in – 8 ft 8.7 in) for captive
females, and 120.0–270 kg (264.6–595.2 lb) and 162.0–230 cm (5 ft
3.8 in – 7 ft 6.6 in) for free-ranging manatees, respectively.[9] The maximum actual Amazonian manatee weight reported is 379 kilograms (836 lb).[9] Calves of the species are born weighing 10–15 kg (22–33 lb) and 85–105 cm (33–41 in) long.[9]
The Amazonian Manatees increase in length approximately 1.6-2.0 mm per
day. This length is measured along the curvature of the body so absolute
length can differ between individuals. As calves, they gain an average
of 1 kilogram per week.[10]
Amazonian manatees, similar to all living manatee species in the family Trichechidae, have polyphyodont teeth. Their teeth are continuously replaced horizontally from the caudal portion of the jaw to the rostral
portion throughout the manatee's life, a unique trait among mammals.
Only the closest living relative of order Sirenia, elephants, show a
similar characteristic of teeth replacement, but elephants have a
limited set of these replacement teeth. As the teeth migrate rostrally
in the manatee, the roots will be resorbed and the thin enamel will wear
down until the tooth is eventually shed. Referred to as cheek teeth,
differentiation of manatee teeth into molars and premolars has not
occurred, and manatees additionally do not have incisors or canine
teeth. These teeth migrate at a rate of about 1–2 mm/month, based on
wear and chewing rates.[12]
The Amazonian manatee lacks nails on its flippers, setting it apart from other manatees.[5]
Additionally, Amazonian manatees have a very small degree of rostral
deflection (30.4°), which can be used as an indication of where in the water column
the animal feeds. A small degree of deflection means that the end of
the snout is straighter with regard to the caudal portion of the jaw.
Animals with a greater degree of deflection, such as D. dugong at
about 70° of deflection, are more of a benthic species, feed on the
seafloor, and have snouts that point almost completely ventrally. Only T. senegalensis
has a smaller rostral deflection of about 25.8°. This is believed to
maximize the efficiency of feeding. A small degree of rostral deflection
allows Amazonian manatees to feed more effectively at the surface of
the water, where much of their food is found.[13]
The Amazonian manatee is the only sirenian that lives exclusively in freshwater habitat.[9]
The species relies on changes in the peripheral circulation for its
primary mechanism for thermoregulation by using sphincters to deflect
blood flow from areas of the body in close contact with water. They also
rely on subcutaneous fat to reduce heat loss.[14]
Manatees have nostrils, not blowholes like cetaceans, which close when underwater to keep water out and open when above water to breathe.[15] Although manatees can remain under water for extended periods, surfacing for air about every five minutes is common.[16][17] The longest documented submergence of an Amazonian manatee in captivity is 14 minutes.[18]
Manatees make seasonal movements synchronized with the flood regime of the Amazon Basin.[8] They are found in flooded forests and meadows during the flood season, when food is abundant.[8]
The Amazonian manatee has the smallest degree of rostral deflection
(25° to 41°) among sirenians, an adaptation to feed closer to the water
surface.[19] It is both nocturnal and diurnal and lives its life almost entirely underwater.[20] Only its nostrils protrude from the surface of the water while it searches river and lake bottoms for vegetation.[20]
The Amazonian and West Indian manatees are the only manatees
known to vocalize. They have been observed vocalizing alone and with
others, particularly between cows and their calves.[21]
The manatees themselves feed on a variety of aquatic macrophytes, including aroids (especially Pistia, aka "water lettuce"[20][22]), grasses, bladderworts, hornworts, water lilies, and particularly, water hyacinths.[23] They are also known to eat palm fruits that fall into the water.[20] Maintaining a herbivorous diet, the manatee has a similar post-gastric digestive process to that of the horse.[19] The manatee consumes approximately 8% of its body weight in food per day.[19]
During the July–August dry season when water levels begin to
fall, some populations become restricted to the deep parts of large
lakes, where they often remain until the end of the dry season in March.[8]
They are thought to fast during this period, their large fat reserves
and low metabolic rates – only 36% of the usual placental mammal
metabolic rate – allowing them to survive for up to seven months with
little or no food.[8]
The Amazonian manatee is a seasonal breeder
with a gestational period of 12–14 months and a prolonged calving
period. Most births take place between December and July, with about 63%
between February and May, during a time of rising river levels in their
native region.[24] After the calf is born, it will begin to eat while staying with its mother for 12 – 18 months.[25]
As of 1977 the population count of the Amazonian manatee was estimated to be around 10,000.
Amazonian manatees occur through most of the Amazon River
drainage, from the headwaters, in Colombia, Ecuador and Peru to the
mouth of the Amazon (close to the Marajó Island) in Brazil over an
estimated seven million square kilometers.[2] However, their distribution is patchy, concentrating in areas of nutrient-rich flooded forest, which covers around 300,000 km2[2]
They also inhabit environments in lowland tropical areas below 300 m
asl, where there is large production of aquatic and semi-aquatic plants;
they are also found in calm, shallow waters, away from human
settlements[2]
The Amazonian manatee is completely aquatic and never leaves the water.[8] It is the only manatee to occur exclusively in freshwater environments.[27]
The Amazonian manatee favors backwater lakes, oxbows, and lagoons with
deep connections to large rivers and abundant aquatic vegetation[27] They are mainly solitary but sometimes they will gather in small groups consisting of up to eight individuals.[25]
They engage in long seasonal movements, moving from flooded areas
during the wet season to deep water-bodies during the dry season[2]
The main threat to the Amazonian manatee is illegal hunting. They are
hunted for subsistent and local use, not commercially. The hunting has
led to the large decline in the population and low population numbers.
Between 1935 and 1954, over 140,000 manatees are estimated to have been
killed. Despite the laws in place against hunting, hunting continues to
occur even in protected areas. Traditional harpoons are the most common weapon used against the manatees, but in Ecuador they are also known to be caught in Arapaima fish traps.[2]
They are mainly hunted for their high value meat but the fat and
skin are also used for cooking and in medicines. The meat is sold
locally to neighbors or at produce markets. It can be illegally sold as
sausage or mixira in public markets in Brazil and Ecuador. Mixira is a
meat preserved in its own fat and is expensive which drives the hunters.[2]
There are no national management plans for the Amazonian Manatee, except in Colombia.
Hunting remains the largest problem and continues in much of its range, even within reserves.[2]
In 1986, it was estimated that the hunting levels in Ecuador were
unsustainable and it would be gone from this country within 10–15 years.[23] While hunting still occurs, an increasing risk to its continued survival in Ecuador is now believed to be the risk of oil spills.[2] The oil exploration also means an increase in boat traffic on the rivers.[2]
The Amazonian manatees of Peru have experienced much of their
decline due to hunting by human populations for meat, blubber, skin and
other materials that can be collected from the manatee.[18] Such hunting is carried out with harpoons, gillnets, and set traps.[18] Much of this hunting occurs in the lakes and streams near the Pacaya-Samiria National Reserve in northeastern Peru.[18] The species is slow-moving, docile, and is often found feeding at the surface of the lakes and rivers it inhabits.[8]
Manatees are also at risk from pollution, accidental drowning in
commercial fishing nets, and the degradation of vegetation by soil
erosion resulting from deforestation.[8]
Additionally, the indiscriminate release of mercury in mining
activities threatens the entire aquatic ecosystem of the Amazon Basin.[8]
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.
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 75–85 cm (30–33 in) 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 colonies, generally on islands and atolls far from the mainland and close to deep water required for foraging. Territorial when breeding, the masked booby performs 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. The second chick born generally does not survive and is killed by its elder sibling. These birds are spectacular plunge 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).
The French naturalist René Lesson was a member of the crew on the La Coquille, captained by Louis Isidore Duperrey, on its voyage around the world undertaken between August 1822 and March 1825.[2]
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 nameSula dactylatra.[3] Lesson subsequently provided a formal description of the masked booby in 1831.[4] The specific epithet combines the Ancient Greekδάκτυλος (dáktul), meaning 'finger', and the Latin ater, meaning 'black'. "Black fingers" refers to the splayed wingtips in flight.[5] The Swedish zoologist Carl Jakob Sundevall described the species as Dysporus cyanops in 1837[6] from a subadult collected in the Atlantic Ocean on 6September 1827.[7] The species name was derived from the Ancient Greek words κύανος (kúanos), meaning 'blue',[8] and ὄψ (óps), meaning 'face'.[9]
The English ornithologist and bird artist John Gould described Sula personata in 1846 from Australia,[10] the species name being the Latin adjective personata, meaning 'masked'.[11] Gould adopted the name Sula cyanops in his 1865 Handbook to the Birds of Australia.[12]
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 priority.[13] The American Ornithological Union followed in the 17th supplement to their checklist in 1920.[14]
"Masked booby" has been designated the official common name by the International Ornithologists' Union (IOC).[15]
The species has also been called the masked gannet, blue-faced booby,
white booby (for its plumage), and whistling booby (for its distinctive
call).[5]
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).[16]
The masked booby is one of six species of booby in the genus Sula.[15] A 2011 genetic study (depicted below) using both nuclear and mitochondrial DNA showed the masked and Nazca boobies (Sula granti) to be each other's closest relatives, their lineage diverging from a line that gave rise to the blue-footed (Sula nebouxii) and 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 million
years ago. Complex water currents in the eastern Pacific may have
established an environmental barrier leading to speciation.[17] Subfossil bones 14,000 years old belonging to the species have been found in deposits on St. Helena Island.[18]
There is a 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.[19] 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.[20]
Breeds in the western Indian Ocean.[21] The German ornithologist Gustav Hartlaub described this taxon in 1859 from Maydh Island off the coast of Somalia near the 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.[22] The subspecies name is derived from the Ancient Greek words μέλανος (mélanos), meaning 'black',[23] and ὄψ (óps), meaning 'face'.
The form breeding on 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. d. fullagari.[24] 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.[25] However, the paleoecologist Richard Holdaway and colleagues cast doubt on the distinctness of the fossil taxon in 2001,[26]
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. d. tasmani as this name has priority over S. d. fullagari.[27]
Fieldwork in the Kermadec Islands indicates the bills of adults are
bright yellow, and that adult males had brighter yellow feet than
females.[28]
A breeding pair of subsp. tasmani and their chick, Norfolk Island
Breeds in the western Indian Ocean.[21] The German ornithologist Gustav Hartlaub described this taxon in 1859 from Maydh Island off the coast of Somalia near the 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.[22] The subspecies name is derived from the Ancient Greek words μέλανος (mélanos), meaning 'black',[23] and ὄψ (óps), meaning 'face'.
The form breeding on 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. d. fullagari.[24] 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.[25] However, the paleoecologist Richard Holdaway and colleagues cast doubt on the distinctness of the fossil taxon in 2001,[26]
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. d. tasmani as this name has priority over S. d. fullagari.[27]
Fieldwork in the Kermadec Islands indicates the bills of adults are
bright yellow, and that adult males had brighter yellow feet than
females.[28]
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;[15] the American biologist Robert Pitman and colleagues found no consistent differences between these three subspecies.[29]
The largest species of booby, the masked booby ranges from 75 to
85 cm (30 to 33 in) long, with a 160–170 cm (63–67 in) wingspan and
1.2–2.2 kg (2.6–4.9 lb) weight. It has a typical 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.[30] The sexes have similar plumage with no seasonal variation, but females are on average slightly heavier and larger than males.[31] The bare skin around the face, throat and lores is described either as black or blue-black. It contrasts with the white plumage and gives a mask-like appearance.[32] The bill of the nominate subspecies is pale yellow with a greenish tinge, sometimes
greyish at the base.[19] Conical in shape, the bill is longer than the head and tapers to a slightly downcurved tip. Backward-pointing serrations line the mandibles.[33] The primaries, secondaries, humerals and 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 coverts.[34] The legs are yellow-orange or olive.[19] The iris is yellow.[35]
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.[19] 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.[28][36]
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,[30]
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.[35]
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.[37]
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.[29] The white morph of the red-footed booby is similar but smaller.[19]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 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.[30]
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.[38] In the eastern Pacific off the coast of Colombia and Ecuador, the masked booby is replaced by the Nazca booby.[29] A vagrant was rescued in 2015 in Newport, Oregon.[39]
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 in New Jersey and New York.[40] There are summer records from Delaware Bay,[41] and Worcester County, Maryland,[42] as well as waters off the coast of Spain.[43]
During the monsoon season (midyear), the masked booby is an
occasional vagrant along the western coast of India, with records from Kerala, Karnataka,[44] and Maharashtra states.[45] It is a vagrant to the Caroline Islands north of New Guinea.[46]
Breeding sites in areas relatively free of vegetation, Oahu
Breeding colonies are located on remote islands, atolls and cays.[30] Lord Howe Island is the southernmost colony.[38] 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 180 to 3,700 m (590 to 12,140 ft) deep.[30]
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.[38]
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.[30]
The largest masked booby colony is on Clipperton Island in the eastern Pacific Ocean,[19]
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.[47]
Clipperton is on a narrow ridge surrounded by deep water.[48]
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.[49] The masked
booby was first recorded breeding on 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.[50] In 2006, two pairs nested in a brown booby colony on Morros del Potosí (White Friars Rocks) near Zihuatanejo in southern Mexico.[51]
Major nesting areas in the Atlantic include Rocas Atoll off the coast of Brazil,[52] Ascension Island in the south Atlantic,[53] and five islands of the Campeche Bank in the Gulf of Mexico.[54][55] The species attempted to nest at Dry Tortugas in the Gulf of Mexico over 1984 and 1985;[56] 19 pairs were recorded there in 1998.[57]
The masked booby generally flies at least 7 m (23 ft) in height, and
at speeds of up to 70 km/h (43 mph). 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.[30]
Regarding the masked booby's longevity, a bird tagged at 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 713 km
(443 mi) away off the Isle of Pines, New Caledonia in July 2004. The longest distance travelled is 3,152 km (1,959 mi); 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.[58]
The masked booby begins breeding by around four or five years of age, though can occasionally do so at three years old.[59] Adults form monogamous
relationships with many pairs remaining together over multiple breeding
seasons. Highly territorial when nesting, single males and mated pairs
engage in 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.[60] 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.[61]
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
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.[61] The twigs and debris are cleared away later as none is actually used in adorning the nest while in use.[37]
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.[37] Eggs are laid between May and September on Lord Howe Island,[49] and early July to early January (peaking in September) on Phillip Island.[50]
In the northern hemisphere, egg-laying on Kure Atoll can be any time from January to early July, peaking in February and March.[62]
On Clipperton Island, egg-laying peaks in November to coordinate with
peak fish productivity of the surrounding waters in January (for growing
chicks).[48] Masked boobies lay at any time in the Caribbean, peaking between March and September.[59]
The nest is a cleared area 0.75 to 1 m (2 ft 6 in to 3 ft 3 in)
in diameter, within which is a clearly demarcated 25 to 30 cm (10 to
12 in) shallow (1–2 cm (0.4–0.8 in) 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.[37] The eggs have an average size of 64 mm × 45 mm (2.5 in × 1.8 in) and weigh
75 g (2.6 oz).[37] They are incubated by both adults for 45 days.[49] Parents incubate the eggs by resting on their 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.[63]
When first hatched, the chicks are about 10 cm (3.9 in) long and weigh
around 40–60 g (1.4–2.1 oz), 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 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.[34] After leaving the nest, young birds are dependent on their parents for 3–4 weeks before dispersing out to sea.[64][65]
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.[66] Siblicide has been observed in the Nazca booby on the Galapagos Islands,[67] and is assumed to occur in
The masked booby is a spectacular diver, plunging vertically or
near-vertically from heights of anywhere from 12 to 100 m (40 to
330 ft)—but more commonly 15 to 35 m (50 to 115 ft)—above the water into
the ocean at high speed, to depths of up to 3 m (9.8 ft) in search of
fish.[68] It generally swallows its catch underwater.[69]
Fieldwork at Clipperton Island showed that masked boobies flew on
average to 103 km (64 mi) from their colony, with a maximum range of
242 km (150 mi), 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.[48] The masked booby forages with the white-bellied storm petrel (Fregetta grallaria) and Bulwer's petrel (Bulweria bulwerii) at times.[70]Frigatebirds often harass the species until they disgorge their catch and steal their food.[19]
Silver gulls (Chroicocephalus novaehollandiae) and buff-banded rails (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.[53][71] The tick species Ornithodoros (Alectorobius) muesebecki was described parasitising nesting blue-faced boobies off the Arabian coast.[72] The argasid tick Ornithodoros capensis and the ixodid tick Amblyomma loculosum have also been recorded as parasites, the latter possibly spreading piroplasmosis caused by Babesia among boobies.[73] On Raine Island and Pandora Cay, nests have been destroyed by green sea turtles (Chelonia mydas) as they pass through booby colonies and dig their own nests in large numbers.[74]
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.[47]
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–
The International Union for Conservation of Nature (IUCN) lists the masked booby as a species of least concern, though the population worldwide is decreasing.[1] 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.[48] 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.[76] 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.[77] The Australian government has rated both subspecies occurring in Australian waters as 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.[78]
Breeding sites in areas relatively free of vegetation, Oahu
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.
