Thermal Insulation of the Down and Feathers of Pygoscelid Penguin Chicks and the Unique Properties of Penguin Feathers

Abstract

Abstract The thermal insulation of the down and feathers of Chinstrap (Pygoscelis antarctica) and Gentoo (P. papua) penguin chicks was measured throughout development in still air and in wind parallel and perpendicular to the plumage. Insulation increased with age. Whole-body insulation of chicks measured in still air (body core to environment) was significantly correlated with the insulation of their pelts at a given age. The insulation of the downy pelts of 10- and 15-day-old chicks was significantly lower than that of all older chicks, and explains the dependence of chicks of that age on continuous brooding by parents, despite their high thermogenic capacities. The down of older chicks provided good insulation in wind speeds of 3-5 m/s. With no wind, the down of Gentoos immediately before molting was a better insulator than feathers of prefledged chicks. The insulation of the feathers of prefledged chicks in parallel air flow up to 5 m/s was 87-112% of its value in still air. However, the insulation increased at higher wind speeds; in Gentoo pelts at winds of 15 m/s, it averaged 136% (maximum 179%) of the insulation in still air. Increasing insulative values of feathers or fur under increasing wind speeds have not been demonstrated previously in any bird or mammal. The insulation of down at various wind speeds and micrometeorological data from the Gentoo Penguin rookery on King George Island, Antarctica were compared. It follows that heat loss of older downy Gentoo chicks is not affected significantly by wind. These chicks can remain within their thermoneutral zones on windy days.