Brood reduction and brood division in coots

The probability of starvation of chicks increases through hatching order in broods of the coot, Fulica atra. After hatching chicks accompany, and are fed by, parents as they swim around the territory. The time that chicks are able to spend outside the nest increases rapidly with age, so that the earlier hatching chicks gain a feeding advantage over the later. Starvation of chicks occurs within 4–5 days of hatching. Even after this initial mortality there persist large differences in the parental feeding rates of individual chicks within a brood. These do not correlate with age and do not seem to be the result of sibling competition. Instead, the parents regulate which chicks accompany them on foraging trips and therefore actively maintain feeding differences within the brood. Chicks cannot counter this parental regulation and the least fed of the brood grow more slowly in spite of an increased self-feeding effort. The possible functions of this parental behaviour are discussed.