Cocos Booby or Blue-footed Booby?
Here's how to tell the difference
Cocos Booby
Blue-footed Booby
Cocos Booby
Sula brewsteri
General Appearance
The Cocos Booby is a medium to large-sized seabird characterized by predominantly white plumage with a contrasting dark brown or blackish head, wings, and tail. This stark dichotomy in color gives the bird an unmistakable appearance in its natural environment. Its long, pointed wings and streamlined body assist in gliding over open waters with ease. The beak is relatively long and pointed, usually yellow in color, and adapts well to catching fish. The webbed feet are particularly suited for both swimming and perching on rocky surfaces.
Male vs Female
In the Cocos Booby, there is minimal sexual dimorphism, meaning males and females are visually similar. Both sexes exhibit the stark white and dark contrasting colors, and any size variation between them is typically negligible. However, during the breeding season, males may show slightly brighter colors around the beak and feet, which are thought to attract females.
Juvenile
Juvenile Cocos Boobies differ from adults in that they tend to have more uniformly brown plumage, which provides better camouflage against predators. As they mature, the white plumage develops gradually, and the dark areas become more pronounced, aligning with adult coloration. The younger birds also have duller colored beaks and feet compared to the vibrant hues seen in adults, which brightens as they age.
Size
26.0 - 33.9 in/37.0 - 57.1 oz
There's more to learn about Cocos Booby
View full detailsBlue-footed Booby
Sula nebouxii
General Appearance
The Blue-footed Booby is a striking seabird best recognized by its bright blue feet and contrasting plumage. Its head and neck are adorned with pale, speckled brown feathers transitioning into a clean white chest. The back and upper wings display a mottled brown shade, while the underparts are a dazzling white. The blue feet are not just for show; their brightness plays a crucial role in attracting mates. Additionally, the species boasts a long, pointed beak designed for diving, complete with sharp, visually stunning bright yellow eyes.
Male vs Female
While males and females exhibit similar coloration and overall appearance, females are generally larger in size, particularly in wingspan. Their blue feet are slightly duller compared to the males, who exhibit a more vibrant hue during the mating season to attract potential mates. The females, on the other hand, have slightly deeper voices than the males, who produce a high-pitched whistling sound.
Juvenile
Juvenile Blue-footed Boobies differ from adults, primarily in their feet, which start off a muted gray before maturing into the iconic blue as they age. Their plumage is duller with more uniform brown feathers, lacking the sharp contrast seen in adults. The juveniles' eyes are dark and absent of the striking yellow seen in adults, and their beaks are duller, lacking the adults' sheen.
Size
25.2 - 35.4 in/52.9 oz
There's more to learn about Blue-footed Booby
View full detailsHow to tell the Cocos Booby from the Blue-footed Booby
Visual differences
The Cocos Booby (Sula brewsteri) and Blue-footed Booby (Sula nebouxii) differ visually in key areas. The Cocos Booby features uniformly white and brown plumage with duller juvenile hues, while the Blue-footed Booby has distinct blue feet and a stronger brown-and-white contrast as adults, with juveniles transitioning from gray feet. The Cocos Booby has a more uniformly colored beak, whereas the Blue-footed Booby's beak has a sheen. The two species are similar in size, with Cocos Booby ranging 26-34 inches long and Blue-footed Booby 25-35 inches, yet the latter is generally heavier (3.3 lbs) compared to the former (2.3-3.6 lbs).
Key differences and behavior
The Cocos Booby (Sula brewsteri) and Blue-footed Booby (Sula nebouxii) share impressive diving skills but differ in several behavioral aspects. Cocos Boobies perform a comical, high-stepping dance focusing on foot movements to attract mates, while Blue-footed Boobies use their striking blue feet in intricate courtship displays. The Cocos primarily inhabit remote tropical Pacific islands, preferring rocky cliffs, while Blue-footed Boobies favor arid coastal regions from California to Peru, often nesting on flat open ground. Both are monogamous, but the Cocos' preference for minimalistic nest sites contrasts with the Blue-footed's simple ground depressions. Their diets are similar, focusing on fish, though Blue-footed Boobies are more inclined towards anchovies and sardines. Neither species visits typical bird feeders, as both are oceanic hunters reliant on marine systems.
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