THE ANIMAL FILES

Blue-footed booby

Sula nebouxii

Blue feet are part of the courtship display.

Blue-footed boobies display coloured feet and dive into the sea for schooling fish. The colour combines skin structure with dietary pigments, while both parents feed chicks by regurgitation. A chick begins with dark feet rather than a miniature adult's brilliant blue.[1]

Follow the evidence ↓
Blue-footed booby
Image: SantiagoGG · Commons · CC BY-SA 4.0
The colour mixture
Skin structure and carotenoids both contribute.[1]
Showing the feet
Males display their feet during courtship.[1]
Diving for a meal
Schooling fish provide important prey.[1]

The colour mixture

Aligned collagen creates a blue structural background, modified by carotenoid pigments acquired from food. Experiments found foot brightness changed with food deprivation. A single colour observation cannot establish an individual’s nutritional state; controlled conditions and the bird’s situation matter.[1]

Showing the feet

Foot colour ranges from pale turquoise to deeper aquamarine. Males lift and display the feet in breeding interactions. Chicks have dark feet and white down, so adult blue coloration is not the starting appearance of every life stage.[1]

Diving for a meal

Boobies plunge after sardines, anchovies and other small fish, and can continue pursuit underwater. Feeding can involve single birds, pairs or flocks. Both male and female return food to chicks by regurgitation.[1]

A COMMON MIX-UP

Are a chick's feet already bright blue?

No. Chicks have dark feet; the adult appearance develops later.[1]

TRY A LITTLE REASONING

Why could foot colour carry information relevant to courtship?

Reveal the explanation

Its brightness responds to nourishment in experiments, and the feet are actively displayed to potential mates.[1]

Sources & editorial notes

Adapted and translated from the cited Wikipedia revisions, with source-linked reasoning. Image credit and licence are listed separately above.

Adapted and translated from Wikipedia contributors; exact revisions are linked below. CC BY-SA 4.0

  1. Wikipedia contributors — Blue-footed booby (cited revision)
  2. NCBI Taxonomy — Sula nebouxii

Last fact check:

One discovery leads to another

Great white pelicanA pouch takes in the water, then lets the water go.Pelecanus onocrotalus ↗Common loonExcellent underwater propulsion comes with an awkward walk ashore.Gavia immer ↗Great blue heronA still heron can be hunting, not resting.Ardea herodias ↗