Why Yellow?

December 7, 2008 7:54 PM

Why are baby chickens and ducks yellow, and not the colors they eventually end up being? Is there some evolutionary advantage to that coloration?
posted by geekhorde to science & nature (12 comments total)

Same color as dried grass, where they hide during the day.
posted by Class Goat at 7:58 PM on December 7, 2008

Also, keep in mind that almost all animal predators are color blind. What may look obvious to your primate eyes won't necessarily be visible to a raccoon or a fox.
posted by Class Goat at 8:01 PM on December 7, 2008

The wife says 'interesting...'

And I thank you sir.
posted by geekhorde at 8:03 PM on December 7, 2008

Only white ones are completely yellow. Wild mallard ducklings are striped. "Wild" type chickens are also brown and yellow.
posted by oneirodynia at 8:19 PM on December 7, 2008

Um. and the white ones are domestic breeds, not found in the wild.
posted by oneirodynia at 8:21 PM on December 7, 2008

Here's a wild duckling. Perhaps the camouflage has been bred out of the domestic ones.
posted by weapons-grade pandemonium at 8:34 PM on December 7, 2008

Here's a pic of Red jungle Fowl chicks. Red Jungle Fowl are believed to be the ancestor of domesticated chickens. You can see that they're marked very similarly to the ducklings weapons-grade pandemonium posted.
posted by oneirodynia at 8:52 PM on December 7, 2008

So to sum up (sorry this is in multiple posts, I'm doing a few things at once): the yellow chicks and ducks are yellow because their down has no pigment; they grow up to be non-pigmented (white) because they've been bred to be that color. You can view lots of different colored baby domestic fowl along with their parents here. Quite a few of the young beasties show tints of the color they are going to be as adults.
posted by oneirodynia at 9:16 PM on December 7, 2008

But some breeds of chicken are black at birth.
posted by Framer at 3:36 AM on December 8, 2008

Heh. There are quite a few answerers questioning the underlying assumptions within the poster's question, which is a good thing and what AskMe is best at. But while the chicken may not be the best example to use, changes in plumage colour with age, diet, habitat changes and hormones are extremely well documented, and a good deal of scientists have looked into the whys and hows of the phenomenon.

The two main pigments that contribute to plumage colour are melanins and carotenoids (which should help with the googling). There are many types of melanins and carotenoids, and they are controlled by a variety of factors (see this review, particularly the "Diet, social behaviours and pigmentation" section).

It's difficult to determine evolutionary pressures that influence any genetic trait*, and questions of evolutionary advantage are similarly difficult (if not impossible) to answer (in a truly rigourous scientific sense). That being said, plumage colour is clearly a strongly (sexually) selected trait, that bears greatly on a bird's social status, so my guess would be that in birds that display a different plumage colour with age, the new colour(s) would likely indicate sexual maturity and therefore aid in finding a mate.

*extremely easy to speculate, extremely difficult to prove.
posted by kisch mokusch at 5:46 AM on December 8, 2008 [1 favorite]

Foxes bred for tamability in a 40-year experiment exhibit remarkable transformations that suggest an interplay between behavioral genetics and development, Lyudmila M. Trut, American Scientist vol. 87 p160, 1999. Among the changes: bright-colored and spotted coats.
posted by fantabulous timewaster at 4:30 PM on December 10, 2008

I was surprised, when I bought my first Audubon Society photographic field guides to wildflowers, that both the eastern and western region guides devoted much larger sections to yellow flowers than any other colors (perhaps larger than all other colors put together, but I don't have access to them right now to confirm this memory). The yellow flowers were remarkably constant in hue from species to species, too, I thought.

I wondered if this could be due to a possible effect on pollinating insects. Lots of insects navigate their longer flights by maintaining a constant angle to the sun or moon (this is why moths mill around your porch light; they evolved for a world where the moon was nearly the only bright light at night, and maintaining a constant angle to a light very far away gives you a straight line, a constant angle to one very near makes for a tight circle). If flowers could come close to mimicking the typically golden hue of the sun near the horizon in the eyes of insects, maybe they could trick enough, under some circumstances, into circling them on their way to hive or nest to improve chances of pollination by those insects.

It's interesting that the wild-type ducklings and chickens linked by weapons grade pandemonium and oneirodynia have black stripes. That suggests mimicry of shadows cast by plants, so perhaps the yellow color is the most favorable to allow the 'poor little guys' to enhance their camouflage by imitating the flowers, as well.
posted by jamjam at 3:44 PM on February 12