Newly hatched American coots carry conspicuous orange-red ornamental feathers on the head, neck and body, contrasting with a bald red crown. The colour is carotenoid-based and disappears as the chick develops, so it is present exactly during the period when parents are dividing food among a large brood.
Field experiments tested whether this matters. When researchers clipped the ornamental plumes from some chicks in a brood, leaving siblings untouched, parents fed the untrimmed chicks more, and those chicks grew faster. The colour therefore functions as a signal that biases parental investment.
The context is a brood that cannot all be raised. Coots lay large clutches, and food often runs short, so parents that concentrate effort on some chicks fledge more young overall. American coots also face brood parasitism from other coots and can recognise and reject foreign eggs, a rare ability among birds. Exactly what the ornament signals about a chick, and why bright colour rather than begging alone should carry that information, is still under discussion.