Red-footed Booby vs Brown Booby

In short

The most reliable field mark to separate Red-footed Booby from Brown Booby in all adult plumages is the color of the feet: Red-footed Booby always has bright red feet, while Brown Booby has duller, non-red feet. Juvenile and immature birds are trickier, but Red-footed Booby juveniles have pale pinkish legs, while Brown Booby juveniles have dull legs. In flight, adult Red-footed Booby (white morph) shows white upperwings with black flight feathers, while Brown Booby always has dark brown upperwings with a white belly. Structure and size also help: Brown Booby is noticeably heavier and bulkier, with a stouter build. Both species can be variable in plumage, so careful attention to bare-part color and wing pattern is essential, especially for immatures.

Identification tips

1. Feet color is diagnostic in adults: Red-footed Booby always has bright red feet in all adult plumages and morphs. Brown Booby never has red feet; their feet are dull and unremarkable. This is the single most reliable field mark.
2. Bare-part coloration: Red-footed Booby adults have a pink-and-blue bill and throat pouch, while Brown Booby has a sharp bill but lacks the pink/blue coloration. Brown Booby males have a blue orbital ring, females a yellow one.
3. Juvenile leg color: Red-footed Booby juveniles have pale pinkish legs, while Brown Booby juveniles have dull, non-pink legs. This can help with immature birds.
4. Plumage contrast (adults): Brown Booby always shows a sharp contrast between dark brown upperparts (head, neck, back, wings) and a clean white belly and lower breast. Red-footed Booby (white morph) is mostly white with black flight feathers; brown morphs are overall brown but may show white on the rump, belly, or tail depending on morph.
5. Juvenile/immature upperwing: Brown Booby juveniles have grey-brown upperwings with darker head and tail, and brown flecking on white underparts. Red-footed Booby juveniles are more uniformly brownish with darker wings, lacking the sharp brown-on-white contrast.
6. Tail color: Red-footed Booby white morph has a white tail; black-tailed white morph has a black tail (can be confused with Masked/Nazca Booby, not Brown Booby). Brown Booby always has a dark tail.
7. Bill shape and color: Both have pointed bills, but Red-footed Booby's is pink-and-blue, while Brown Booby's is duller and sharper, with no pink/blue coloration.
8. Size and structure: Brown Booby is heavier and bulkier, with a more robust build and shorter wings, resulting in a faster flap rate. Red-footed Booby is smaller, more slender, and appears more agile in flight.
9. Flight style: Red-footed Booby is more agile and efficient in the air, while Brown Booby has a faster, more direct flap due to shorter wings.
10. Nesting behavior: Red-footed Booby often nests in trees, while Brown Booby nests on the ground or low cliffs. Tree-nesting is a strong clue for Red-footed Booby.
11. Habitat context: Brown Booby is more likely to be seen over inshore waters and is generally more common and widespread. Red-footed Booby prefers remote islands and is less likely to be seen near populated areas.
12. Sexual dimorphism: Brown Booby shows some sexual dimorphism in orbital ring color (blue in males, yellow in females); Red-footed Booby sexes are similar in plumage and bare parts.
13. Vocalizations: Not a reliable separation; Brown Booby may grunt or quack, but both are generally silent.
14. Pitfalls: Beware of Red-footed Booby brown morphs, which can appear similar to Brown Booby but will always show red feet and different bill coloration. Juvenile Brown Booby can be confused with Red-footed Booby immatures, but leg and bill color, as well as the pattern of brown on white, are key.
15. When in doubt: Focus on the feet and bill color first, then check for the sharpness of the brown/white contrast on the body and the nesting location if visible.

Size

Brown Booby is distinctly larger and heavier than Red-footed Booby. Brown Booby averages about 1266.5 g in body mass, compared to Red-footed Booby's 998 g. Brown Booby females can reach up to 80 cm in length and 150 cm in wingspan, while Red-footed Booby is smaller at about 70 cm in length and up to 152 cm in wingspan. The difference in mass and bulk is often visible in the field, with Brown Booby appearing more robust and solid, while Red-footed Booby is more slender and agile.

Plumage

Juvenile and immature birds: Brown Booby juveniles already resemble adults, with grey-brown upperparts, darker head and wings, and underparts heavily flecked brown on white. Their legs are dull, never bright. Red-footed Booby juveniles are brownish overall with darker wings and pale pinkish legs, lacking the sharp brown-on-white contrast of Brown Booby.

Adults: Red-footed Booby is highly variable, with multiple morphs. The white morph is mostly white with black flight feathers, sometimes with a yellowish head tinge. The brown morph is overall brown, but the white-tailed brown morph has a white belly, rump, and tail. All adult Red-footed Boobies have bright red feet and a pink-and-blue bill/throat pouch. Brown Booby adults have a sharply demarcated dark brown head, neck, and upperparts, with a contrasting clean white belly and lower breast. Their bare parts are not red; males have a blue orbital ring, females a yellow one. The bill is sharp and the wings are short and pointed.

In flight, the contrast between the dark upperparts and white belly of Brown Booby is striking, while Red-footed Booby (white morph) shows a mostly white bird with black flight feathers, and brown morphs are overall brown but can show white on the tail and belly depending on morph.

Behaviour

Red-footed Booby is agile in flight, using wind efficiently, but is clumsy during takeoff and landing. It often nests in trees and forages by catching flying fish or shallow diving. Brown Booby is gregarious, commuting and foraging at low height over inshore waters, with a fast flap rate due to its shorter wings. Both species are colonial nesters, but Red-footed Booby is more likely to be seen perched in trees, while Brown Booby is more often seen on the ground or low rocks.

Habitat

Both species are widespread in tropical oceans and often overlap in range. Red-footed Booby breeds mostly on remote islands, frequently nesting in trees, which reduces predation. Brown Booby is more common and widespread, often found over inshore waters and nesting on the ground or low cliffs. If you see a booby nesting in a tree, it is almost certainly a Red-footed Booby; ground nesters in mixed colonies are more likely Brown Booby, especially on accessible islands.

Voice

Both species are generally silent, but Brown Booby may occasionally make grunting or quacking sounds. Red-footed Booby is not noted for distinctive vocalizations in the sources provided, so voice is not a reliable field mark for separation.