blue-footed booby

blue-footed booby, (Sula nebouxii), large seabird inhabiting arid islands and coastal areas along the eastern Pacific Ocean from Baja California in Mexico south to Peru. The species is distinguished from the cormorants, gannets, and other boobies classified in the family Sulidae by its blue webbed feet. Like several other members of this family, however, blue-footed boobies plunge-dive into the ocean for fish. The species, which is also known for its awkward gait and its indifference to people (an animal behavior that has allowed for the bird’s extensive study), derives its common name from bobo, a Spanish word meaning “foolish” or “clownish.” Blue-footed boobies are divided into two subspecies: S. nebouxii nebouxii is found along the Pacific coasts of North America and South America, whereas S. nebouxii exisa inhabits the Galapagos Islands.

Natural history

Adult blue-footed boobies are predominantly brown in color with white undersides and a neck with feathers that alternate between brown and white. In addition to the birds’ aforementioned blue feet, they have gray-blue facial disks that terminate in long gray beaks. They are moderately large birds, with females being slightly larger than males (see also sexual dimorphism). In adults, body length ranges from 81 to 90 cm (31.9 to 35.4 inches), with a weight that averages between 1.5 and 2 kg (3 and 4.5 pounds). Fully grown blue-footed boobies also have long, brown, wedge-shaped wings, which together measure 1.5 meters (5 feet). The down of juvenile birds is white, which is later replaced with grayish brown and brown plumage as the birds age. Young also begin life with whitish feet.

The species observes its prey from the sky before diving from heights of 30 meters (100 feet) into the water. Blue-footed boobies hunt for fish in groups, and they communicate with each other aloft by whistling to alert others of the presence of fish. The species is adapted for diving and swimming; its nostrils are permanently closed, and it possesses a specialized air sac in the skull. This air sac protects the bird from the impacts associated with striking the ocean and the pressures that come with swimming as deep as 25 meters (80 feet) below the surface. Blue-footed boobies prey on anchovies, sardines, mackerel, and flying fish, as well as squid. The species has few natural predators, though Galapagos hawks and short-eared owls prey on eggs and chicks that inhabit the Galapagos Islands.

Blue-footed boobies are monogamous, and they form pairs that last as least as long as the breeding season. Blue-footed boobies can also breed throughout the year. Courtship begins with a male gifting stones or other small objects to a female, before he performs an elaborate high-stepping display. The male’s blue feet are essential to this process; the blue coloration is derived from the intake of carotenoids, a pigment found in fish. Females are attracted to mates with a brighter color blue, which is an indicator of the male’s maturity and health. Studies also indicate that males show a preference for females with vibrant blue feet rather than females with duller-colored feet.

Females incorporate the objects presented to them by the males as the foundation of their nests, which are made in small depressions in the ground. After fertilization, female blue-footed boobies lay two to three eggs in the nest. Both parents use their feet, which are laden with blood vessels that transmit heat, to incubate the eggs until the eggs hatch 41–45 days later. Both parents provide food to their chicks, with the male bringing home most of the food for the chicks’ first month of life, while the female protects and warms the chicks by supporting each of them on the tops of her feet. During the second month, after which the chicks leave the nest and go off on their own, the female becomes the principal food provider. Studies have shown that during food shortages, the parents will withhold food from smaller chicks in order to provision the largest. Both sexes reach sexual maturity by age 6; however, some females are capable of breeding as early as age 1, and some males become sexually mature as early as age 2. Blue-footed boobies can live as long as 18 years in captivity.

Conservation status

Although blue-footed booby populations have undergone a modest decline in the early 21st century, the International Union for Conservation of Nature and Natural Resources (IUCN) has classified the blue-footed booby as a species of least concern since 2004. The IUCN notes that the blue-footed booby’s large geographic range combined with its slow rate of population decline does not warrant making it a priority for conservation; however, scientists note that periodic climatic phenomena (such as El Niño) and the effects of climate change and ocean acidification appear to be reducing the abundance of prey in some areas, such as the Galapagos Islands, which has resulted in local population declines.