An interesting behavior, in relation to the care of offspring by the American coot, was discovered by a team of researchers at the University of California at Santa Cruz. The American coot is a waterbird with grey or black feathers and a white beak that mostly frequents the wetlands of North America. Unlike their parents, the chicks have very brightly coloured feathers and beaks between red and orange.
This difference had already been noted by previous studies and, again, other studies had shown that the parents seem to prefer the more brightly coloured chicks when it comes to feeding their offspring. However, no study had explained the reason for this strange behaviour. It was succeeded by the professor of ecology and evolutionary biology Bruce Lyon who, together with his colleague Daizaburo Shizuka from the University of Nebraska-Lincoln, published a study on Proceedings of the National Academy of Sciences.
Initially the researchers had thought that it was the chick, through evolutionary pathways, that could manipulate parents to get more food. However, in the course of the experiments that the researchers carried out, using, among other things, a photospectrometer to measure the precise color gradations of more than 1500 coot chicks, they found that this behavior is related to another one that sees mothers feed more some chicks instead of others to make sure that at least part of them can survive in strength since the available food is almost never enough for everyone.
The researchers initially discovered the mother, during the first 10 days after hatching the eggs, showed no preferences and fed all the chicks in which way. However, 10 days after the last hatching, the parents began to check the food allocation to ensure that at least one of the chicks could grow in strength. The latter began to receive preferential feeding and grew faster, becoming stronger and more resilient. However, parents tend to choose the chicks that are born later, which are, incidentally, the most colourful. In comparison with the others, he carries out a sort of aggression called “tousling”: he shakes them by the back of the neck to prevent them from eating too much.
“The male and the female share the brood, with each parent feeding only their half of the brood, and each parent also chooses a favourite. The colour predicts which one they choose, therefore the ornament can serve as signal for telling them which chick needs the maximum help,” explains Lyon himself. “They start by creating an irregular playing field, which allows them to break down the brood, and then they intervene to level the field. Orange plumage seems to be a feature that helps them do that.”
Among other things, this also explains why the eggs that mothers lay in the nests of other mothers, a behaviour known as “brood parasitism” and typical also of other species of birds, are less coloured. The eggs that the females lay in the nests of strangers are the first in the laying sequence and therefore are characterized by a lower pigment. With this preferential behaviour, parents are therefore more likely to feed their own child than the child of another.