What’s brown, white and blue, and moves like a TikTok dance challenge? A 3.3 pound (1.5 kilogram) wild ocean bird that’s named after a Spanish insult and whose numbers are slipping into endangered territory.
We’re talking about the blue-footed booby (Sula nebouxii). These birds, with their dark brown wings and signature bright blue feet, stand about 32 inches (81 centimeters) in height and are one of a half-dozen species in the family Sulidae. They have long bills, cigar-shaped bodies and narrow, angular wings. Along with the salt-and-pepper coloring of its body, the blue-footed booby has a high-stepping mating dance the males use to attract females. Male boobies raise one foot at a time in a move known as sky-pointing that’s accompanied by horizontally extended wings, raised heads and a long, hollow-sounding call.
But don’t expect to hear a cacophony when the bird is flying or hunting. “The blue-footed booby is one of those unique birds that hardly makes a sound when at sea,” says Diana Ludwiczak, owner of the “How I Got Into Veterinary School” blog, who became fascinated with blue-footed boobies when she joined a student avian club. “When and if you get the rare opportunity to hear a blue-footed booby squabble over prey it’s easy to melt into a million pieces. Their vocalizations will delight and satisfy any amateur bird enthusiast.”
And so may their webbed feet. This particular feature, when found on aquatic birds like blue-footed boobies, are known as totipalmate feet. This means that all four toes of the foot are joined by webbing that makes the birds’ feet as efficient as flippers in the water. Webbed feet also help blue-footed boobies regulate their body temperature. If they become too cold, they can balance on one leg and tuck the other foot into their downy white belly feathers. If they become too hot, the average blue-footed booby cools off by pooping on its own cerulean feet.
A Nickname That Stuck
The blue-footed booby is believed to have gotten its name from early explorers who cannibalized the Spanish word “bobo.” The word at the time meant, loosely, “stupid.” It referred largely to the way booby birds moved clumsily on land and the unwitting way they approached humans without fear.
The reference stuck, but so did our fascination with learning more about the bird, including its population counts and reproduction rates. Researchers have studied their habitats, mating rituals, parenting styles and food preferences, and even the penchant of older siblings to peck their younger sibling competitors to death.
About half the population of blue-footed boobies lives in the Galápagos Islands, a chain of 19 volcanic islands in the Pacific Ocean about 605 miles (1,000 kilometers) west of South America. The islands are part of their closest neighboring country, Ecuador, which in 1959 declared 97 percent of the islands’ land area a national park and preserved the surrounding waters as a marine reserve. This declaration was preceded by Charles Darwin’s visit to the islands in 1835, where the flora and fauna developing in extreme isolation inspired his evolutionary theory.
The other half of the blue-footed booby population ranges along the western coasts of North, Central and South America, with most of these coastal denizens concentrated in Mexico, Columbia, Ecuador and Peru. The blue-footed boobies leave their nesting grounds at daylight to hunt their preferred prey, which takes them on flights over cold oceanic water to fertile areas where deep swells ascend to the surface and are rich with sardines, anchovies and small fish of the open sea. Occasionally, blue-footed boobies dine on squid as well, diving — as they do to catch all prey — into the water from great heights at high speed and snapping their targets in their beaks as they rise toward the surface. Even during egg-rearing season, male and female pairs will take turns flying out to catch dinner, with one staying behind to keep the eggs warm.
Rocky Homelife, Successful Flock
Like other seabirds, the blue-footed booby nests on land and doesn’t seem to mind the rocky terrain of shorelines or volcanic islands. Unlike other birds that build elaborate nests in hopes of wooing a mate, the blue-footed booby’s successful courtship culminates instead in a humble abode. A female lays one to three eggs, and both partners sleep in a nest that is built by doing what comes naturally — defecation.
As the mated pair (they usually only bond for one breeding season) occupies a scrape or depression in rock, they create a circular walled nest over time built with layer upon layer of poop. But all is not always well within those walls. Male boobies unsure of egg paternity with a new female may destroy the eggs. Other booby species may maraud the nest and break the eggs. And, because the eggs hatch four days apart from each other, older chicks may kill the newly hatched competition.
Each new generation highlights the reason blue feet work for the booby. The color comes from carotenoid pigments that are ingested in the bird’s fresh fish-rich diet. Any bird that is weak or unhealthy will struggle to feed itself and therefore will not command the brightest blue for its feet. The intensity of blue, whether weak or strong, signals the male’s health and potential as a mate, which means that breeding females can make a decision by looking at a male’s feet during a mating dance.
“Male blue-footed boobies are evaluated by potential mates by the blueness of their feet,” says Lisa M. Webb, a licensed clinical psychologist who recently completed a master’s degree in environmental health and conservation science at Johns Hopkins University, which included collecting data on blue-footed boobies in the Galápagos Islands. “This blueness is an indicator of health and strength, so a female will choose a mate with vivid dark blue feet, as that suggests a greater probability of healthy offspring.”
Although being able to judge a male’s virility by his blue feet would appear to streamline dating decisions, blue-footed booby populations have been shrinking. Largely because of declining sardine numbers, the blue-footed booby has gone from about 20,000 adults in the Galápagos Islands to fewer than 6,500 in 2018, the latest year for which data is available.