Bright Young Coots

An American coot (Fulica americana) parent feeds its highly ornamented chick.

Bruce Lyon

Bright color displays on adult birds are often used for courtship. However, adult American coots (Fulica americana) are a drab, dark gray to black, while their chicks have red-orange heads, beaks, and feathers. Previous studies have shown that coot parents give more food to brighter-colored chicks. A new study finds that these brighter chicks tend to be younger and smaller than their siblings, suggesting that parents use color to help identify and favor chicks who would otherwise be at a disadvantage.

Bruce Lyon of the University of California Santa Cruz and Daizaburo Shizuka of the University of Nebraska–Lincoln observed 1,431 American coot chicks in 310 nests in British Columbia wetlands from the time eggs were laid to the time parents stopped feeding their chicks, usually ten to twenty-five days after hatching. They recorded the order in which eggs were laid and hatched, the redness of each chick’s beak and chin feathers, and whether either parent gave more food to one chick over the others.

The researchers found that chicks that were laid and hatched later in each brood were redder. Because coot chicks often die from starvation, with only about half of each nest surviving to independence, the researchers speculate that parents use color to select one of the surviving young chicks to feed, giving it a leg up on its older and larger siblings.

To determine whether parents use hatching order or redness to choose a chick to favor, the researchers added eggs to thirty nests so that more than one egg would hatch each day. In these nests, redder chicks were not favored when they were the same age as their adopted siblings, indicating that parents use color to select which chicks to favor only when those chicks vary in age.

American coots are brood parasites; they sometimes lay eggs in another bird’s nest. The researchers ruled out a previous hypothesis that coloration was a means for parasitic chicks to attract more attention from host parents. Instead, Lyon and Shizuka found that parasitic chicks are typically laid early in the brood, are less red, and are not favored by their host parents. (Proceedings of the National Academy of Sciences)