One of the most famous and charismatic inhabitants of the Galapagos island, the blue-footed booby, is almost like a cartoon character.
With their bright blue feet taking centre stage, it begs the question…
Why do they have blue feet?
One reason is actually a similar reason to the feather colour of flamingos, this is due to their diet.
In the blue-footed boobies, it’s from pigments called carotenoids with higher concentrations making the feet a more intense colour of blue.
This pigment comes from the fish they eat.
Interestingly these carotenoid pigments also act as immune system boosters in the boobies.
Still, once they are incorporated into the feet, they can no longer be used for immunity or detoxification.
So why then, would individuals use pigments to colour their feet at a direct cost of their immune system?
They do it for love
The answer is the same reason why most animals do anything in the wild, they do it for love or courtship as more of a technical term.
During courtship, a male booby conducts a foot-flaunting dance, just like the one you see below, to try and impress the females.
Males with brighter feet appear to be more successful at securing a mate than those with dull feet, so foot colour seems to be a sexually selected trait.
An obvious question now would be: why are blue feet so attractive to females? The answer to this lies in what the colour of the feet signifies.
Why are females attracted to the blue?
Research has shown that the blueness of a male boobies feet is a reliable indicator of the health and strength of the bird.
If a male is unhealthy, weak or old, it will generally not be as good at securing food as a healthy male, resulting in a reduced concentration of carotenoids and hence, duller feet.
Having bright feet signifies that an individual is strong and healthy and can afford to use more carotenoids for foot colouration, even though this doesn’t seem like it’s a conscious decision made by the bird.
So it appears that the blue feet for which this species is so famous for are a result of a trade-off between immune function and signalling to attract a mate.
Studies have even shown that the foot colour reflects paternal contribution to raising offspring, so chicks raised by brighter footed males grow faster than those raised by duller footed males.
Taking all of this into consideration, its no wonder why blue feet are so attractive!
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