You are what you eat
Why Are Flamingos Pink?
The colour is not theirs. It is taken out of their food and moved into their feathers.
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Step 1 of 5
A flamingo chick is grey.
It hatches a dull grey-white and stays that way for a year or two. Whatever makes the adults pink is clearly not something they are born with.
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Step 2 of 5
The colour is a chemical from the food chain's bottom.
Certain algae make a reddish-orange pigment. Brine shrimp eat the algae and turn pinkish themselves, and flamingos eat the shrimp.
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Step 3 of 5
The bird moves the pigment into growing feathers.
The pigment is absorbed in the gut, carried in the blood and laid down in feathers and skin as they grow. A feather already grown cannot change.
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Step 4 of 5
Take the food away and the colour fades.
Zoo flamingos fed plain fish go pale within a year. Keepers add the same pigment to their feed on purpose to keep them pink.
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Step 5 of 5
Which makes the colour worth showing off.
Only a well-fed bird in good feeding grounds gets properly pink, so the colour is honest news about a mate. The pinkest birds pair up first.
A parent feeds its chick on a bright red crop milk, and loses much of its own colour doing so.
The short version
Flamingos are pink because pigment from the algae and shrimp they eat is carried into their feathers as those feathers grow.
Try it yourself
Look at a carrot and a flamingo feather. The pigment doing the work is a close relative in both — eat enough carrot and your own skin goes faintly orange.