Why do blue-footed boobies have blue feet? And 8 other blue-footed booby facts

Clumsy on land but incredibly agile in the air, blue-footed boobies (Sula nebouxii) are seabirds that are recognized by their bright blue feet.

Residing in the arid, tropical, and subtropical islands off the Pacific coast of South America,¹ blue-footed boobies are one of six species of boobies (genus Sula).² Often lounging on objects and surfaces near the water with no caution regarding humans,³ many of these birds can be found in Mexico’s Gulf of California, Peru and the Galápagos Islands.²

These birds can be captivating creatures, collectively diving from a variety of heights into schools of fish under the surface.⁴

Here are 9 facts you might not know about blue-footed boobies!

1. How did blue-footed boobies get their name?

The blue-footed booby name originates from the Spanish word “bobo,” which means silly or foolish. These birds tend to have a lack of regard for possible danger, making them vulnerable at times.⁴

2. Why do blue-footed boobies have blue feet?

Blue-footed boobies’ blue feet come from the nutrients of fresh fish they eat. The blue pigment can indicate if a blue-footed booby is nourished. The more pigmented the blue, the healthier the bird.²

3. What do blue-footed boobies eat?

Fresh fish make up most of a blue-footed booby’s diet. Mostly hunting in groups, these boobies can dive into schools of fish from heights as high as 100 feet, as well as catch flying fish mid-air. They also feed on sardines, anchovies, mackerel, and at times, squid and offal. With air sacs that provide their brains protection from the pressure, blue-footed boobies can go 80 feet below the water surface to hunt.⁴

4. What is the mating process for blue-footed boobies?

Boobies associate brighter feet with youth, fertility, and a higher competence when it comes to raising offspring, and they take that into consideration when choosing a mate.² The male, after deciding on a female to court, will flash the brightness of his feet around her by exaggerating his walk with higher and wider steps. Prior to mating, both birds will perform a courtship dance known as “displaying” that involves tilting their beaks toward the sky and raising their wings.⁴

5. What threats do blue-footed boobies face?

As climate change and ocean acidification accelerate, blue-footed boobies and many other seabirds are at risk of harm.⁵ In particular, their food sources are at risk. 

6. What are the differences between a male and female blue-footed booby?

Female blue-footed boobies are slightly larger than males, allowing them to dive into deeper waters and carry more food.⁵ Males have larger tails and smaller pupils than females. Females also tend to have brighter blue feet than male blue-footed boobies.²

7. Where do blue-footed boobies lay their eggs?

Blue-footed boobies lay their pale bluish eggs on the ground without a nest.¹ To incubate the eggs, the male and female will take turns using their feet to keep the eggs warm during the incubation period. Out of the two or three eggs that are initially laid, usually one or two hatch.² The parent birds defecate while incubating, leaving a circle of feces around the nest called guano.⁵

8. How do blue-footed boobies stay cool?

Blue-footed boobies stay cool through evaporative cooling—a method that uses evaporation to cool the air—by vibrating the bones in their throats to flutter the surrounding skin. They will also use a cooling mechanism called urohidrosis that involves defecating and urinating on their feet!³

9. How do blue-footed boobies communicate?

Blue-footed boobies communicate with each other through grunts and whistles that can be piercing and have multiple syllables. Both males and females can distinguish the call of their mates from other birds.²

[1] “Species Spotlight: Blue-Footed Booby | Pages | WWF.” World Wildlife Fund, https://www.worldwildlife.org/pages/species-spotlight-blue-footed-booby.

[2] “Blue-Footed Booby Articles- Encyclopedia of Life.” Encyclopedia of Life, https://eol.org/pages/45509067/articles.

[3] “Blue-Footed Booby Overview, All About Birds, Cornell Lab of Ornithology.” Online Bird Guide, Bird ID Help, Life History, Bird Sounds from Cornell About Birds, https://www.allaboutbirds.org/guide/Blue-footed_Booby/overview.

[4] Harris, Marie. “Sula Nebouxii, Blue-Footed Booby.” Animal Diversity Web, https://animaldiversity.org/site/accounts/information/Sula_nebouxii.html

[5] “Blue-Footed Booby Life History, All About Birds, Cornell Lab of Ornithology.” Online Bird Guide, Bird ID Help, Life History, Bird Sounds from Cornell About Birds, https://www.allaboutbirds.org/guide/Blue-footed_Booby/lifehistory.