Blue-footed booby

Blue-footed Booby
Conservation status
	; Least Concern (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Order:	Suliformes
Family:	Sulidae
Genus:	Sula
Species:	S. nebouxii
Binomial name
	Sula nebouxii; Milne-Edwards, 1882
	Range shown by red area

The Blue-footed Booby (Sula nebouxii) is a bird in the Sulidae family which includes ten species of long-winged seabirds. The natural breeding habitat of the Blue-footed Booby is tropical and subtropical islands of the Pacific Ocean, most famously, the Galápagos Islands, Ecuador.

Etymology

The name booby comes from the Spanish term bobo (which means 'stupid' or 'fool' or 'clown') because the Blue-footed Booby is, like other seabirds, clumsy on land.^[2]

Description

The Blue-footed Booby is on average 81 cm (32 in) long and weighs 1.5 kg (3.3 lb), with females being slightly larger than males. It has long pointed wings and a wedge shaped tail. They have strong, thick necks. The booby's eyes are placed on either side of their bill and oriented towards the front, enabling excellent binocular vision. The Blue-footed Booby's eyes are yellow. The male has more yellow in its iris than the female. The Blue-footed Booby has permanently closed nostrils made for diving, necessitating breathing through the corners of their mouths. Their feet range from a pale turquoise to a deep aquamarine in color. Males and younger birds are observed to have lighter feet than females.^{[citation needed]}

Distribution and habitat

Blue-footed Boobies are distributed among the continental coasts of the eastern Pacific Ocean to the Galápagos Islands and California.^{[citation needed]}

The Blue-footed Booby is strictly a marine bird. Their only need for land is to breed, which they do along rocky coasts.^{[citation needed]}

Breeding

The courtship of the Blue-footed Booby consists of the male flaunting his blue feet and dancing to impress the female. During the dance, the male will spread his wings and stamp his feet on the ground. The Blue-footed Booby is a monogamous animal although they may have the potential to be bigamous.^[3] They reunite at their breeding grounds. The breeding cycle of the booby is every 8 to 9 months.^{[citation needed]} When mating, the female parades and the male points his head and tail high to the sky and his wings back to show off to the female. The male Blue-footed Booby also makes a high-piping whistle noise. Males do a dance to attract the females. The dance includes the males lifting their blue feet high and throwing their heads up. The blue-footed booby is not a seasonally reproducing species. They are opportunistic breeders.^{[citation needed]}

Foot pigmentation

The brightness of male foot colour is dependent on access to food.^[4] The male's foot colouration is extremely sensitive, with changes perceivable by female birds within a 48 hour period. As the Blue-footed Booby is a monogamous species with biparental care,^[4] the female is able to make day-by-day alterations to her investment in the pairing, dependent on male quality, which makes male foot colour a secondary sexual characteristic. During egg laying, the female is able to alter her reproductive investment through changing egg size, dependent on the perceived quality of her male partner.

As well as short-term variation, the strength of male foot colour has been shown to decrease in the long term as senescence proceeds, probably due to the effects of oxidative damage.^[5]

Rearing young

The female Blue-footed Booby lays two or three eggs. 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 (a patch of bare skin on the underbelly), it uses its feet to keep the eggs warm. The chicks cannot control their body temperature up until about one month old. Eggs are laid about five days apart. Blue-foots are one of only two species of booby that raise more than one chick. This may be because of the males specialized diving in shallow waters. They must be fed frequently, so the adults constantly hunt for fish. The 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. Boobies may use and defend two or three nesting sites until they develop a preference a few weeks before the eggs are laid. Usually two to three eggs are laid, and one to two chicks are hatched. The incubation period is 41–45 days. They nest on bare black lava in a small dip in the ground. The female will turn to face the sun throughout the day, so the nest is surrounded by excretion. These nests are done in large colonies. The male and female share quite a bit of their 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.

Brood Reduction

The Blue-footed booby is an excellent model animal to study because of its small brood size, easily accessible nest, and high tolerance to human proximity. Many studies have been done in the past few decades regarding parent-offspring conflict and siblicidal brood reduction.

Brood hierarchy due to Asynchronous Hatching

The Blue-footed booby lays one to three eggs in one nest at a time, although 80% of nests only contain two eggs.^[6] The two eggs are laid five days apart. After the first egg is laid, it is immediately incubated, resulting in a difference in chick hatching times. The first chick is hatched four days before the other, so it gets a four-day head start in growth compared to its younger sibling. This asynchronous hatching serves two main purposes. It spaces out the difficult period where newborn chicks are too feeble to accept regurgitated food and also reduces the chance of total brood loss to predators such as the milk snake ^[7] . Experiments have shown that asynchronous hatching may also reduce sibling rivalry. Experimentally manipulated synchronous broods produced more aggressive chicks, while in asynchronous broods chicks were less violent since a clear brood hierarchy was more easily established. Although asynchronous hatching is not vital for the formation of brood hierarchies (the experimentally synchronous broods established them as well), it does aid in efficient brood reduction when food levels are low. The subordinate chicks in asynchronous broods died more quickly. Thus relieving the parents of the burden of feeding both offspring when resources are insufficient to properly do so.^[8]

Facultative Siblicide

Blue-footed booby chicks practice facultative siblicide, which means causing the death of a sibling based on environmental conditions. The chick that hatches first, often referred to as the A-chick, will kill the younger, B-chick, if there is a food shortage. The A-chicks grow faster than B-chicks and this initial size disparity is retained for at least the first two months of life.^[9] During lean times, the A-chick may attack the B-chick by pecking vigorously, or it may simply drag its younger sibling by the neck and oust it from the nest. Experiments where the necks of chicks were taped to inhibit food ingestion showed that sibling aggression increased sharply when the weight of the A-chicks dropped below 20-25% of their potential in weight. There was a steep increase in pecking below that threshold, indicating that siblicide is triggered by the dominant chick’s weight, and not simply by the size difference between the siblings. It was also discovered that younger broods (those less than six weeks old) had three times the rate of pecking than older broods. This is perhaps due to the relative inability of younger brood B-chicks to defend themselves from the attack.^[10] The elder sibling also harms the younger one by controlling access to the food delivered by the parents. A-chicks always receive food before B-chicks. This is not for lack of trying on the B-chick’s part, since subordinate chicks beg just as much as dominant ones. However, the dominant chicks are able to divert the parents’ attention to themselves, as their large size and conspicuity serve as more effective stimuli^[11].

However, another experiment showed that booby chicks do not operate exclusively by the leftovers hypothesis, where younger chicks are fed only after the elder ones are completely satiated. The researchers found that there is a certain degree of tolerance of the younger sibling during short-term periods of food shortages. This tolerance hypothesis presents that the elder chicks will reduce food intake moderately, just enough so that the younger sibling does not starve. Although this system works during short-term food shortages, it is unsustainable during prolonged periods of dearth, because then the elder sibling becomes aggressive and siblicidal.^[12]

Parental Role in Siblicide

Blue-footed Booby parents are passive spectators of this intrabrood conflict. They do not intervene in their offspring’s struggles, even when they are upon the point of siblicide. Booby parents even appear to facilitate the demise of the younger sibling by creating and maintaining the inequality between the two chicks. They reinforce the brood hierarchy by feeding the dominant chick more often that the subordinate one. Thus, they respond to the brood hierarchy and not to the level of begging when deciding which chick to feed, as both chicks beg in equal amounts. This level of passivity towards the very possible death of their younger offspring may be an indication that brood reduction is advantageous for the parents.^[13] The Insurance egg hypothesis views the second egg and resulting chick as insurance for the parent in case the first egg does not hatch, or if food levels are higher than expected. ^[14] The parents’ behavior may make it seem like they are cooperating with the elder, dominant chick, and there appears to be very little evolutionary conflict between the parents and the A-chick.

However, Booby parents may not be as indifferent as they seem. The parental behavior may in actuality be masking parent-offspring conflict, as the following experiments indicate. One team of researchers discovered that Blue-footed Booby parents make steep-sided nests that serve to deter the early ejection of the younger chick by the older one. This is in direct contrast to another species of Booby, the Masked Booby, where siblicide is obligate due to the ease in which older siblings can eject younger ones from their flat nests. When the blue-footed Booby nests were experimentally flattened, the parents restored them to their original steepness. ^[15] In another experiment, Blue-footed Booby chicks were swapped into nests of the Masked Booby. These chicks were then more likely to engage in siblicide, which reveals that the type of parental care somehow affects the level of siblicde. ^[16] Parents also appeared to respond more frequently to chicks that were in poorer body conditions during periods of food deprivation. ^[17] 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. Heavier eggs give rise to heavier chicks that have greater fitness, which indicates that parents may have tried to level the playing field from the start to give the second chick a heightened chance of survival. ^[18] Hormonal analysis of eggs also shows that there appears to be no parental favoritism in regards to androgen allocation, meaning that androgen levels are about the same in both eggs. However, the researchers note that this could be because the species have evolved more simple ways to manipulate asymmetries in order to maximize the parents’ reproductive output.^[19] Thus, these 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.

Hunting and feeding

The Blue-footed Booby's diet consists mainly of fish. Blue-footed Boobies are specialized fish eaters feeding on small school fish like sardines, anchovies, mackerel, and flying fish. They also feed on squid and offal.^{[citation needed]} The Blue-foot dives into the ocean, sometimes from a great height, and swims underwater in pursuit of its prey. It hunts singly, in pairs, or in larger flocks. They 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 the rest of the group and they will all dive together. Surprisingly, individuals do not eat with the hunting group, preferring to eat on their own, usually in the early morning or late afternoon.^{[citation needed]}

When they spot a school of fish, they will all dive in unison. They will point their bodies down like arrows and dive into the water. Plunge diving can be done from heights of 33–100 ft (10–30.5 m) and even up to 330 ft (100 m). These birds hit the water around 60 mph (97 km/h) and can go to depths of 82 ft (25 m) below the water surface.^{[citation needed]} The prey are usually eaten while the birds are still underwater. Males and females fish differently, which could contribute to the reasons that Blue-foots — unlike other boobies — raise more than one young.^{[citation needed]} The male is smaller and the tail is larger for its body, which enables the male to fish in shallow areas instead of just deep waters. The tail can flatten out, enabling him to change direction in the shallow water. The female is larger and can carry more food. The food is then regurgitated to the young. The males feed the young for the first part of the incubation period. This is done because the males can bring back food more quickly than the female. When the demand for more food increases, the female provides the food to the young.^{[citation needed]}

Communication

Blue-foots will make raucous or polysyllabic grunts or shouts and thin whistle noise. 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.

Mates can recognize each other by their calls. In a recent study, researchers have analysed calls of blue-footed boobies and did a playback experiment. An individual signature was present and acoustic variables differed between sexes. Individual identity was encoded by temporal (male) and spectral (female) parameters. Male and female signals were equally effective for mate recognition. The decoding process (acoustic cues used to encode the individual identity) may differ between the sexes^[20]

Gallery

Male courtship display
On Seymour Island
On Española
On Isla de la Plata
Displaying by raising a foot
Keeping an egg cool
Booby with Offspring at the Galapagos Islands
Blue footed Booby on North Seymour Island,Galapagos
In flight
In flight

References

^ Template:IUCN
^ 'Blue-Footed Booby Sula nebouxii' NationalGeographic.com
^ Castillo-Guerrero, José Alfredo; Mellink, Eric; Aguilar, Aarón (2005). "Bigamy in the Blue-Footed Booby and the Brown Booby?". Waterbirds. 28 (3): 399–401. doi:10.1675/1524-4695(2005)028[0399:BITBBA]2.0.CO;2. JSTOR 4132556.
^ ^a ^b Velando, Alberto; Beamonte-Barrientos, René; Torres, Roxana (2006). "Pigment-based skin colour in the blue-footed booby: An honest signal of current condition used by females to adjust reproductive investment". Oecologia. 149 (3): 535–42. doi:10.1007/s00442-006-0457-5. PMID 16821015.
^ Torres, Roxana; Velando, Alberto (2007). "Male reproductive senescence: The price of immune-induced oxidative damage on sexual attractiveness in the blue-footed booby". Journal of Animal Ecology. 76 (6): 1161–8. doi:10.1111/j.1365-2656.2007.01282.x. PMID 17922712.
^ Velando, Alberto (2003). "Differential body condition regulation by males and females in response to experimental manipulations of brood size and parental effort in the blue-footed booby". Journal of Animal Ecology. 72. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
^ Drummond, Hugh (1986). "Parent-Offspring Cooperation in the Blue-footed Booby (Sula nebouxii): Social Roles in Infanticidal Brood Reduction". Behavioral Ecology and Sociobiology. 19 (5): 365–372. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
^ Osorno, Jose Luis (1995). "The Function of Hatching Asynchrony in the Blue-footed Booby". Behavioral Ecology and Sociobiology. 37 (4): 265–273. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
^ Drummond, Hugh (1986). "Parent-Offspring Cooperation in the Blue-footed Booby (Sula nebouxii): Social Roles in Infanticidal Brood Reduction". Behavioral Ecology and Sociobiology. 19 (5): 365–372. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
^ Drummond, Hugh (1989). "Food Shortage Influences Sibling Aggression in the Blue-footed Booby". Animal Behavior. 37: 806–819. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
^ Drummond, Hugh (1986). "Parent-Offspring Cooperation in the Blue-footed Booby (Sula nebouxii): Social Roles in Infanticidal Brood Reduction". Behavioral Ecology and Sociobiology. 19 (5): 365–372. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
^ Anderson, D. J. (1995). "Evidence of Kin-Selected Tolerance by Nestlings in a Siblicidal Bird". Behavioral Ecology and Sociobiology. 37 (3): 163–168. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
^ Drummond, Hugh (1989). "Food Shortage Influences Sibling Aggression in the Blue-footed Booby". Animal Behavior. 37: 806–819. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
^ Velando, Alberto (2003). "Differential body condition regulation by males and females in response to experimental manipulations of brood size and parental effort in the blue-footed booby". Journal of Animal Ecology. 72. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
^ Anderson, David J. (1995). "The Role of Parents in Siblicidal Brood Reduction of Two Booby Species". The Auk. 112 (4): 860–869.
^ Loughweed, Lynn W. (1999). "Parent Blue-footed Boobies Suppress Siblicidal Behavior of Offspring". Behavioral Ecology and Sociobiology. 45 (1): 11–18.
^ Villasenor, Emma (2007). ""Honest Begging in the Blue-footed Booby: Signaling Food Deprivation and Body Condition". Behavioral Ecology and Sociobiology. 61 (7). {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
^ D'Alba, Liliana (2007). "Seasonal Egg-Mass Variation and Laying Sequence in a Bird with Facultative Brood Reductions". The Auk. 124 (2): 643–652. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
^ Drummond, Hugh (2008). "Do Mothers Regulate Facultative and Obligate Siblicide by Differentially Provisioning Eggs with Hormones?". J. Avian Biology. 39. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
^ "Males use time whereas females prefer harmony: individual call recognition in the dimorphic blue-footed booby". Retrieved 5 July 2012. {{cite web}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)