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Sula sulared-footed booby

By Rebecca Frank

Geographic Range

Red-footed boobies are found in tropical and sub-tropical waters across the globe (they are found in the Oriental, Ethiopian, Neotropical, and Australian regions; they are also found on oceanic islands). They take long hunting trips of up to 150 km from their breeding grounds but do not migrate. One of the largest populations is on the Galapagos Islands. (Alten, 1998; del Hoyo, et al., 1992; eNature.com, 2002)

Habitat

Red-footed boobies make their nests in the tops of trees on islands and coasts in tropical regions. They may also nest in low scrub. They inhabit islands and coastal regions in the tropics, because they prey on fish in pelagic regions of the ocean. (Alten, 1998; del Hoyo, et al., 1992; eNature.com, 2002; Raikow, 2004)

Physical Description

Sula sula is the smallest booby, and is well suited for its long flights out to sea in search of prey. It has strong neck muscles, and a wedge-shaped tail. It has a long, tapering bill with serrated cutting edges to help catch and eat its prey. Its external nostrils are closed to allow for plunge-diving, but it has developed secondary nostrils beside the mouth which are automatically covered by flaps when it plunges. The skin around its face is generally bare. The eyes are beside the bill, face forward, and have very pale irises. The wings are long, pointed, and situated fairly far back on the body. They help the bird to fly in high winds (which it does by alternating powerful flaps with gliding) and also to dive. When diving, the wings close around the body of the bird, making it more aerodynamic. The legs are short and strong, and the feet are large and totipalmate (webbed between all four toes). The feet are highly vascular because it is through the feet that heat is transmitted from the parent to the offspring. The legs are set far back on the body, helping it to swim. The feet and legs are also red, thus giving the bird its name. Sula sula is very buoyant, having developed a series of air-sacs which are extensions of the bronchi. They help in its plunge-diving.

The plumage of Sula sula must serve two purposes, camouflage and body temperature maintenance. The underpart of the bird is generally white, so as to provide countershading to help prevent its prey from seeing it. Also, "in an environment where both salt and the sun intensify the effects of feather abrasion, dark, melanin-rich feathers on the upper parts help to provide stronger resistance" (del Hoyo et al., 1992). The plumage is molted continuously so as not to hinder the bird's flight capability at any one time, however, molt is suspended during breeding. Feathers are renewed 1 to 2 times yearly. Sula sula lacks a brood patch because it would interfere with streamlining and insulation. There are several morphs of this bird, often making it difficult to identify without noting the color of its feet. The morphs are: the white-tailed brown morph, the white headed and white tailed brown morph, the white morph (which has black on its wings), the black-tailed white morph (found on the Galapagos Islands), and the golden white morph (found on the Christmas Islands).

Red-footed boobies are 70 to 71 cm long, on average and have a wingspan of 91 to 101 cm. They weigh from 900 to 1003 g. Females tend to be slightly larger than males. (Alten, 1998; del Hoyo, et al., 1992; eNature.com, 2002; Raikow, 2004)

  • Sexual Dimorphism
  • female larger
  • Range mass
    900 to 1003 g
    31.72 to 35.35 oz
  • Range length
    64 to 76 cm
    25.20 to 29.92 in
  • Average length
    70-71 cm
    in
  • Range wingspan
    91 to 101 cm
    35.83 to 39.76 in

Development

The Red-Footed Booby lays a single egg. The eggs are a pale color, and are covered in a chalky residue. The parent keeps the egg warm by placing its feet on the egg. As the parent stands on the egg, it is usually very strong. The egg is generally 5% of the mother's total weight. Incubation lasts for 41-45 days, and the parents take turns guarding/warming it in stints which last anywhere from 12-60 hours. Upon hatching, the chick is near-naked, having no feathers. It broods on the feet of its parents for the first few days, and is not left unattended until is is approximately one month old when it can regulate its own body temperature. Chicks are generally a whitish-brown color. The young feed from the parent, eating from it's mouth. The fledgling phase lasts from 100-139 days, and post-fledgling care lasts for about 190 days. Juveniles are brown or grayish-brown with yellow-gray legs. Red-Footed Boobies molt several times per year, going through several stages between the brown juvenile and the white adult. They are ready to breed at 2-3 years.

(del Hoyo, 1992; Nelson, 1978.)

Reproduction

Since red-footed boobies are colonial and highly social, mating/courtship rituals and displays are very important. The higher the population density, the more ritualized their behavior. They show off their wings and feet, and display postures. Movement is displayed by the "Bill-Up-Face-Away" posture. The "Facing-Away" and "Bill Tucking" postures inhibit aggression. Males posture with their tails, beaks, and wings facing upward and call for mates. Once a monogamous pair mates, they will return to the same nest year-to-year to mate. (Alten, 1998; del Hoyo, et al., 1992)

Red-footed boobies mate approximately once every 15 months, depending on food availability. They are known for their somewhat flimsy, unstable nests which are often damaged by storms. They often build their nests in trees. Their choice of nest location may be a way to avoid competition for space, since other species of boobies nest on the ground. Pairs mate and lay one egg at a time, raising that egg to maturity. Incubation lasts between 41 and 45 days and the young fledge as young as 91 days old. In El Niño Southern Oscillation years (when food is scarce) fledging may occur at more than 139 days old (Schreiber et al., 1996). Red-footed boobies reach maturity in two to three years. (del Hoyo, et al., 1992; Schreiber, et al., 1996)

  • Breeding interval
    Breeding occurs every 15 months.
  • Breeding season
    Breeding is not seasonal.
  • Range eggs per season
    1 to 1
  • Average eggs per season
    1
    AnAge
  • Range time to hatching
    41 to 45 days
  • Range fledging age
    91 to >139 days
  • Range age at sexual or reproductive maturity (female)
    2 to 3 years
  • Range age at sexual or reproductive maturity (male)
    2 to 3 years

Red-footed boobies nest colonially with hundreds of mating pairs together in one location. Pairs mate and lay one egg at a time, raising that egg to maturity. Incubation lasts between 41 and 45 days and the young fledge in one month. Both the male and female red-footed booby care for the altricial young. If food is scarce the parents may abandon the young in order to ensure their own survival, but if food is abundant they may care for the juvenile for a long time, teaching it how to hunt. Because this bird has such a long lifespan, it can afford to raise one juvenile at a time, and still produce many young during its lifetime. (del Hoyo, et al., 1992)

  • Parental Investment
  • no parental involvement
  • altricial
  • pre-hatching/birth
    • protecting
  • pre-weaning/fledging
    • provisioning
      • male
      • female
  • pre-independence
    • provisioning
      • male
      • female

Lifespan/Longevity

Red-footed boobies live as sexually reproductive adults for approximately 23 years but can live for more than 40 years.

  • Range lifespan
    Status: wild
    40 (high) years
  • Average lifespan
    Status: wild
    23 years
  • Average lifespan
    Status: wild
    275 months
    Bird Banding Laboratory

Behavior

Red-footed boobies are highly social birds, and as such have developed highly ritualized behaviors. They have colonial nesting grounds, with as many as several hundred pairs in one location. They can breed in mixed colonies, living with other Sulids. They are mostly diurnal, but have also been known to hunt nocturnally when squid come to the surface of the water. Feather care, particularly oiling, is important as it prevents waterlogging and helps with heat retention. This "involves a bird impregnating its plumage with the waterproofing secretion produced by the preen gland at the base of its tail" (del Hoyo et al., 1992). Other heat regulating methods include exposing the webs of the feet and possibly excreting on them for evaporative cooling. Another method of heat loss is for the bird to hang its wings away from its body to increase its surface area and allow more heat to escape from its body. In order to retain/acquire heat, the bird may sun itself with its wings spread, to allow the dark feathers to absorb heat. The fishing trips that it takes out to sea may last for several days, as it flies farther out than any other Sulid. It may also follow ships out, and use them to perch. (Alten, 1998; del Hoyo, et al., 1992)

Home Range

We do not have information on home range for this species at this time.

Communication and Perception

There are a variety of calls used by red-footed boobies. Male and female calls are different, due to structural differences in the trachea and syrinx. The male produces mild, plaintive whistles while the female produces trumpeting honks or quacks. The juveniles sound like females. The posturing that is typically used in courtship is also a form of communication. (del Hoyo, et al., 1992)

Food Habits

Sula sula preys on fish. It is known to hunt up to 150 km out to sea, much farther than other Sulids. It plunge-dives to moderate depths (approximately 4 to 10 m) in order to acquire fish, which it catches and swallows on its return to the surface. Red-footed boobies can fly higher than other Sulids (10 to 30 m) when searching for food because of their binocular vision. Once prey are sighted, the bird will dive straight down into the water, reaching its top speed just before entry. The larger females can often catch food that is deeper than the smaller males because of their weight. Sometimes it will also use its wings to swim deeper underwater (15 to 20 m) to reach prey. Red-footed boobies can also catch prey in midflight, due to their smaller size and better agility than other species of booby. This is a particularly effective method for hunting flying fish as they jump out of the water. They are also known to hunt squid at night, as their large eyes allow effective nocturnal hunting. Red-footed boobies are communal hunters and once one bird has spotted food, all will dive. The food is swallowed before the bird emerges from the water; this prevents other individuals from stealing it.

Two favorite foods of red-footed boobies are flying fish, which they are often able to catch in midflight, and squid (that they catch during night hunting). However, they will eat whatever fish are available. (Alten, 1998; del Hoyo, et al., 1992; eNature.com, 2002)

  • Animal Foods
  • fish
  • mollusks

Predation

Due to the fact that this particular bird lives in isolated oceanic areas, and often spends much of its time very far from land, it does not have many predators.

Ecosystem Roles

Red-footed boobies play an important role in their ecosystem; they have an impact on the fish that they prey on. They do not interact with many other organisms, as they live in such isolated marine areas, often staying far out to sea. (Alten, 1998)

Economic Importance for Humans: Positive

In some areas people rely on red-footed boobies as a food source. In the past, people who hunted them were always aware of the detrimental effects of their hunting, and as such were cautious not to overhunt the populations. Today, people collect sulids and their eggs and sell them across the world. This has gotten out of control and the exploitation has become a concern.

Conservation parks have been established so that people can visit and enjoy these birds without harming them. (del Hoyo, et al., 1992)

Economic Importance for Humans: Negative

There are no known adverse affects of red-footed boobies on humans.

Conservation Status

Sula sula is not globally threatened, because it is so widely dispersed. It is one of the most abundant and widespread of all the Sulids. Despite this, the population size has been decreasing steadily over recent centuries. The biggest threats to these birds are deforestation and the fishing industry. Because they live in trees, deforestation destroys their habitat/nesting grounds, and the fishing industry depletes their food source.

While they are not threatened on a global level, in some areas human pressure on their habitats is threatening specific populations. In addition, people collect sulids and their eggs and sell them across the world. This has gotten out of control and the exploitation has become a concern. Red-footed boobies are protected in some areas now. Conservation parks have been set up so that people can visit and enjoy these birds without harming them. Red-footed boobies are protected under the US Migratory Bird Treaty Act. (Alten, 1998; del Hoyo, et al., 1992)

Other Comments

It has been proposed that the name "booby" comes from the spanish word "bobo" meaning stupid or dunce and refers to the bird's characteristic lack of fear of man.

Contributors

Alaine Camfield (editor), Animal Diversity Web.

Rebecca Frank (author), University of Michigan-Ann Arbor, Kerry Yurewicz (editor), University of Michigan-Ann Arbor.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

choruses

to jointly display, usually with sounds, at the same time as two or more other individuals of the same or different species

coastal

the nearshore aquatic habitats near a coast, or shoreline.

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

diurnal
  1. active during the day, 2. lasting for one day.
ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

food

A substance that provides both nutrients and energy to a living thing.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pelagic

An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).

piscivore

an animal that mainly eats fish

polymorphic

"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

scrub forest

scrub forests develop in areas that experience dry seasons.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

year-round breeding

breeding takes place throughout the year

References

Alten, M. 1998. A Tale of Three Boobies. International Wildlife, 28(1): 28.

Gough, G., J. Sauer. 2002. "Patuxent Bird Glossary, Patuxent Wildlife Research Center" (On-line). Accessed 03/08/04 at http://www.mbr-pwrc.usgs.gov/.

Nelson, B. 1978. The Sulidae: Gannets and Boobies. NY: Oxford University Press.

Raikow, R. 2004. "Grolier Multimedia Encyclopedia" (On-line). Accessed 03/08/04 at http://gme.grolier.com/.

Rauzon, M., D. Drigot. 1999. Red-Footed Booby Use of Artificial Nesting Platforms. Waterbirds, 22(3).

Schreiber, E., R. Schreiber, G. Schenk. 1996. Red-footed booby (Sula sula). Birds of North America, 241: 1-19. Accessed November 14, 2006 at http://bna.birds.cornell.edu/BNA/account/Red-footed_Booby/.

del Hoyo, J., A. Eliott, J. Sargatal. 1992. Handbook of the Birds of the World, Vol. 1 (Ostrich to Ducks). Lynx Editions.

eNature.com, 2002. "Red-footed Booby" (On-line). Accessed 03/08/04 at http://www.enature.com/.

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