Instruct: Given a question, retrieve passages that answer the question.
Query: What do blue-footed boobies eat?
The natural breeding habitats of the blue-footed booby are the tropical and subtropical islands of the Pacific Ocean. It can be found from the Gulf of California down along the western coasts of Central and South America down to Peru. Approximately one half of all breeding pairs nest on the Galápagos Islands.[3] Its diet mainly consists of fish, which it obtains by diving and sometimes swimming underwater in search of its prey. It sometimes hunts alone, but usually hunts in groups.[4]
The blue color of the blue-footed booby's webbed feet comes from carotenoid pigments obtained from its diet of fresh fish. Carotenoids act as antioxidants and stimulants for the blue-footed booby's immune function, suggesting that carotenoid-pigmentation is an indicator of an individual's immunological state.[17] Blue feet also indicate the current health condition of a booby. Boobies that were experimentally food-deprived for forty-eight hours experienced a decrease in foot brightness due to a reduction in the amount of lipids and lipoproteins that are used to absorb and transport carotenoids. Thus, the feet are rapid and honest indicators of a booby's current level of nourishment.[17] As blue feet are signals that reliably indicate the immunological and health condition of a booby, coloration is favored through sexual selection.
Blue-footed boobies make raucous or polysyllabic grunts or shouts and thin whistling noises. The males of the species have been known to throw up their head and whistle at a passing, flying female. Their ritual displays are also a form of communication.
However, booby parents may not be as indifferent as they seem. Experimental evidence suggests that the parental behavior described above may be masking parent-offspring conflict. It was discovered that blue-footed booby parents make steep-sided nests that serve to deter the early ejection of the younger chick by the older sibling. This is in direct contrast to the masked booby, a species in which siblicide is obligate due to the ease in which older siblings can eject younger chicks from their flat nests. When blue-footed booby nests were experimentally flattened, parents restored them to their original steepness.[31] In another experiment, blue-footed booby chicks that were placed in masked booby nests were more likely to engage in siblicide, which reveals that parental care somehow affects the level of siblicide.[32] Parents also appear to respond more frequently to chicks that are in poorer body conditions during periods of food deprivation.[33] Egg-mass analysis shows that in clutches produced at the beginning of the breeding season, the second egg in a nest were, on average, 1.5% heavier than the first. Since heavier eggs give rise to heavier chicks that have greater fitness, this evidence indicates that parents may try to rectify any disadvantages that accompany a late hatching date by investing more into the second egg.[34] Hormonal analysis of eggs also shows that there appears to be no parental favoritism in regards to androgen allocation. It is important to note, however, that this may simply be that the species has evolved simpler ways to manipulate asymmetries and maximize parental reproductive output.[35] Experiments show that what may at first appear to be parental cooperation with the elder chick may in fact mask a genetic parent-offspring conflict.[36]
The name booby comes from the Spanish word bobo ("stupid", "foolish", or "clown") because the blue-footed booby is, like other seabirds, clumsy on land.[3] They are also regarded as foolish for their apparent fearlessness of humans.[2]
Blue-footed boobies are less likely to commit siblicide and if they do, they commit it later after hatching than masked boobies. In a study, the chicks of blue-footed and masked boobies were switched to see if the rates of siblicide would be affected by the foster parents. It turns out that the masked boobies that were placed under the care of blue-footed booby parents committed siblicide less often than they would normally. Similarly, the blue-footed booby chicks placed with the masked booby parents committed siblicide more often than they normally did, indicating that parental intervention also affects the offspring's behavior.
Sea birds (magnificent frigatebird, brown booby, masked booby, terns, double-crested cormorant ("Phalacrocorax auritus"), pelican, petrels) nest on the cliffs and uninhabited islands. In particular, on Grand-Îlet, a natural reserve of the archipelago which houses species of booby found nowhere else on "les Saintes": red-footed booby ("Sula sula") and blue-footed booby ("Sula nebouxii"). But in the context of global warming and invasive foreign species implanted by the humans (e.g. red lionfish), the environment and the biodiversity of these islands are considered to be very vulnerable and to be protected. It is therefore recommended that visitors do not take plants or capture animals to avoid disturbing the species in their natural biotope, and do not pollute the ecosystem.
In these three booby species, hatching order indicates chick hierarchy in the nest. The A-chick is dominant to the B-chick, which in turn is dominant to the C chick, etc. (when there are more than two chicks per brood) Masked booby and Nazca booby dominant A-chicks always begin pecking their younger sibling(s) as soon as they hatch; moreover, assuming it is healthy, the A-chick usually pecks its younger sibling to death or pushes it out of the nest scrape within the first two days that the junior chick is alive. Blue-footed booby A-chicks also express their dominance by pecking their younger sibling. However, unlike the obligately siblicidal masked and Nazca booby chicks, their behavior is not always lethal. A study by Lougheed and Anderson (1999) reveals that blue-footed booby senior chicks only kill their siblings in times of food shortage. Furthermore, even when junior chicks are killed, it does not happen immediately. According to Anderson, the average age of death of the junior chick in a masked booby brood is 1.8 days, while the average age of death of the junior chick in a blue-footed booby brood may be as high as 18 days. The difference in age of death in the junior chick in each booby species is indicative of the type of siblicide that the species practices. Facultatively siblicidal blue-footed booby A-chicks only kill their nest mate(s) when necessary. Obligately siblicidal masked and Nazca booby A-chicks kill their sibling no matter if resources are plentiful or not; in other words, siblicidal behavior occurs independently of environmental factors.
There are no subspecies of Peruvian booby, but some members of the species have been seen to hybridize with blue-footed boobies.
Like other sexually size-dimorphic birds, female blue-footed boobies usually favor the smaller sex during times of food scarcity. Booby chicks do not show clear differences in size based on sex, but females do grow faster than males, which means they require greater parental investment. Blue-footed boobies display behavior that is described in the Flexible Investment Hypothesis, which states that a female will adjust the allocation of resources to maximize her lifetime reproductive success. This was shown in an experiment in which females had their flight feathers trimmed, so that they had to expend more energy during flights to obtain food for their broods. Female chicks of such mothers were more strongly affected than their brothers, in that they had lower masses and shorter wing lengths.[25]
This species is distinctive, and only likely to be confused with species that do not generally share its range. The Cape gannet is a rare vagrant to Australasian waters and has an all-black tail, while the masked and red-footed boobies are generally restricted to tropical waters. Although both have mostly white plumage, they lack the buff colouring of the head and have white tails. The masked booby has a blue-black face and less black on the wing, while the red-footed booby has red feet.
In one experiment, siblicide was shown to be somehow related to parental care. When non-obligate siblicidal blue-footed boobies were swapped with obligate siblicidal masked booby chicks, it was found that the blue-footed chicks exhibited more siblicidal behavior.
Concerns of a decline in the booby population of the Galápagos Islands prompted a research project in its cause. The project, completed in April 2014, confirmed the population decline.[38] The blue-footed booby population appears to be having trouble breeding and thus is slowly declining. The decline is feared to be long-term, but annual data collection is needed for a firm conclusion that this is not a normal fluctuation.
The blue-footed booby is on average 81cm (32in) long and weighs 1.5kg (3.3lb), with the female being slightly larger than the male. Its wings are long and pointed and brown in color. The neck and head of the blue-footed booby are light brown with white streaks while the belly and underside exhibit pure white plumage.[12] Its eyes are placed on either side of its bill and oriented towards the front, enabling excellent binocular vision. Its eyes are a distinctive yellow, with the male having more yellow in its irises than the female. Blue-footed booby chicks have black beaks and feet and are clad in a layer of soft white down. The subspecies S. n. excisa that breeds on the Galápagos Islands is larger than the nominate subspecies and has lighter plumage especially around the neck and head.[9]
The blue-footed booby is a specialized fish eater, feeding on small schooling fish such as sardines, anchovies, mackerel, and flying fish. It will also take squid and offal. The blue-footed booby hunts by diving into the ocean after prey, sometimes from a great height, and can also swim underwater in pursuit of its prey. It can hunt singly, in pairs, or in larger flocks. Boobies travel in parties of about 12 to areas of water with large schools of small fish. When the lead bird sees a fish shoal in the water, it will signal to the rest of the group and they will all dive in unison, pointing their bodies down like arrows.[4]
The blue-footed booby is one of only two species of booby that raises more than one chick in a breeding cycle.
The female blue-footed booby lays two or three eggs. Eggs are laid about four to five days apart. Both male and female take turns incubating the eggs, while the non-sitting bird keeps watch. Since the blue-footed booby does not have a brooding patch, it uses its feet to keep the eggs warm. The incubation period is 41–45 days. Usually, one to two chicks are hatched from the two to three eggs originally laid. The male and female share parental responsibilities. The male will provide food for the young in the first part of their life because of his specialized diving. The female will take over when the demand is higher.[10] Chicks feed off the regurgitated fish in the adult's mouth. If the parent blue-footed booby does not have enough food for all of the chicks, it will only feed the biggest chick, ensuring that at least one will survive.[5]
The island is frequented by sea turtles, which come to reproduce there, but it is the home of the seabirds: magnificent frigatebird ("Fregata magnificens"), brown booby, masked booby, terns, double-crested cormorant ("Phalacrocorax auritus"), pelican, petrels nest on the cliff of the island. Red-footed booby ("Sula sula") and blue-footed booby ("Sula nebouxii") are only observable on Grand-Îlet, among the islands of Guadeloupe department. The waste of these birds results in a strong concentration of guano on the rocks and beaches.
The blue-footed booby (Sula nebouxii) is a marine bird native to subtropical and tropical regions of the eastern Pacific Ocean. It is one of six species of the genus Sula – known as boobies. It is easily recognizable by its distinctive bright blue feet, which is a sexually selected trait. Males display their feet in an elaborate mating ritual by lifting them up and down while strutting before the female. The female is slightly larger than the male and can measure up to 90cm (35in) long with a wingspan of up to 1.5m (5ft).[2]
Boobies are another group of seabirds known for their mating displays. Brown ("Sula leucogaster"), red-footed ("S. sula") and blue-footed boobies ("S. nebouxii") have at least nine described parts to their mating display. Sky pointing in boobies is similar to albatrosses; in the brown booby, sky pointing is described as a display where the male throws his head backwards, stretches his neck out, and usually gives a whistling vocalization. Parading is a well-known display in boobies as well; in this display, one individual in the pair - usually the male - walks upright, with his tail erect, swaying in an exaggerated manner from side to side while taking small steps. In blue-footed and red-footed boobies, parading also includes lifting and flaunting their brightly colored feet at their prospective partner.
The blue-footed booby is monogamous, although it has the potential to be bigamous.[16] It is an opportunistic breeder, with the breeding cycle occurring every 8 to 9 months.[22] The courtship of the blue-footed booby consists of the male flaunting his blue feet and dancing to impress the female. The male begins by showing his feet, strutting in front of the female. Then, he presents nest materials and finishes the mating ritual with a final display of his feet.[23] The dance also includes "sky-pointing", which involves the male pointing his head and bill up to the sky while keeping the wings and tail raised.[24]
Mates can recognize each other by their calls. Researchers have analyzed calls of blue-footed boobies and conducted playback experiments. Although calls differed between sexes, unique individual signatures were present. It was found that both males and females can discriminate the calls of their mates from others.[37]
Food problems may be the cause of an observed failure of the birds to even try to breed. The results of the research suggest this is related to a decline in sardines (Sardinops sagax), an important part of the boobies’ diet. Earlier work on Española Island saw successful breeding in blue-footed boobies that have access to sardines, in which case their diet consists essentially wholly of sardines. However, sardines have been largely absent from the Española area since 1997, as has been shown from Nazca boobies there, who also prefer sardines but can breed using other prey. In 2012–13, roughly only half of prey items in the boobies' diet were sardines. No evidence was seen of other possible causes for the decline, such as effects of humans, introduced predators, or disease.[39]
Compared to other species of boobies such as the blue-footed booby, siblicide is obligatory in the masked booby. One reason is because the masked boobies build very shallow flat nests, so older chicks can expel their younger siblings with relative ease. Blue-footed booby parents, meanwhile, build nests with steeper sides, thus preventing some older chicks from engaging in siblicidal behaviour.
Red-footed boobies are spectacular divers, plunging into the ocean at high speeds to catch prey. They mainly eat small fish or squid which gather in groups near the surface.