Down Feather - Function

Function

The loose structure of down feathers traps air, which helps to insulate the bird against heat loss and contributes to the buoyancy of waterbirds. Species that experience annual temperature fluctuations typically have more down feathers following their autumn moult. There is some evidence that down feathers may also help to decrease the incidence of nestling cannibalism among some colonially nesting species, as the stiffness of the feathers make the young more difficult to swallow. Pollutants can reduce the efficiency of these functions. When oiled, for example, down feathers mat and clump together, which breaks down the bird's insulation and allows water to reach the skin.

Female wildfowl use down feathers plucked from their own breasts to line their scrape nests. This process performs the dual function of helping to insulate the eggs and exposing the female's brood pouch—an area of bare skin, rich in blood vessels, which transmits heat very efficiently. Of the various items birds use to line their nests, down feathers provide the most effective insulation, though only when dry; wet down is the least effective insulator. Down may also help camouflage the eggs when the female is away from the nest, particularly as the birds often draw the feathers over their eggs before leaving.

Because a bird can eliminate heavy metals in its feathers and because feathers can be collected non-invasively and stored indefinitely, down feathers can be used to check for evidence of metal contamination in the bird's environment. Studies have shown a high level of correlation between the level of metal contamination in a bird's diet and the level found in its feathers, with the proportion of the chemicals found in its feathers remaining relatively constant (and relatively high for some metals).