That is a question a team of biologists have been asking for quite some time and, as is typical in science, the answer was not what they first expected. Previous studies conducted by this same laboratory concluded that coot parents preferentially feed chicks that display brighter coloration. The goal of the present study was to determine why this was the case.
The researchers noted that coots lay between 8-10 eggs and these eggs hatch in the order they were laid. Additionally coots are nest predators and lay eggs in other coots nests. One hypothesis was that the chicks hatched from predatory eggs were the more brightly colored chicks and thus would have gotten fed more. This turned out to be false. The researchers discovered that the chicks hatched from the latter laid eggs were the more brightly colored. Typically chicks hatched latter in a brood have to catch-up to their larger siblings if they are to survive. The researcher noted that if these smaller and brightly colored latecomers survived the parents would use their coloration as a way to preferentially feed these chicks more and allow them to catch-up to their earlier siblings. 2
A wonderful survial strategy reveled in a nicely done study. Hat’s off to science and to the coot.
1. University of California – Santa Cruz. “The mysterious case of the ornamented coot chicks has a surprising explanation: The bright colors of the chicks of American coots help their parents choose favorites, according to a new study.” ScienceDaily. ScienceDaily, 31 December 2019. www.sciencedaily.com/releases/2019/12/191231111817.htm.
2. Bruce E. Lyon, Daizaburo Shizuka. Extreme offspring ornamentation in American coots is favored by selection within families, not benefits to conspecific brood parasites. Proceedings of the National Academy of Sciences, 2019; 201913615 DOI: 10.1073/pnas.1913615117