Study

Wettability and Phylogenetic Development of Feather Structure in Water Birds

Rijke, A. M.

Journal of Experimental Biology, 1970

Peer-reviewedcomparative studylaboratory

What they did

Feather barb spacing and diameter were measured across water bird families and related to how readily the plumage wets, testing whether water repellency is a geometric property of the feather surface rather than a property of applied oil.

Studied in: Aves, Spheniscidae, Phalacrocoracidae
Sample size: feather geometry and wetting measurements across water bird families

What they found

Water repellency tracks the geometry of barbs and barbules — their diameter and spacing — rather than the presence of preen oil. Families that stay dry have geometries in which water cannot penetrate between the barbs; cormorants, which wet readily, do not.

What it means

The authors' reading, and ours. Where they differ, that difference is the point.

How the authors put it

Plumage water repellency in birds is primarily a structural property of feather geometry.

How NatureHQ reads it

The correction here is one people find genuinely surprising: preen oil is not what makes a waterproof bird waterproof. The structure does it, and the oil maintains the structure — keeping feathers flexible and in condition so the geometry holds. That is why an oiled seabird dies of cold rather than of poisoning: pollutant oil destroys the geometry, and no amount of preening rebuilds it. The paper is old and its framework has been refined, but the structural conclusion has held.

Limitations

Older work using measurement techniques since superseded.
Penguin plumage is unusually dense and short, so extrapolation from other water birds is imperfect.
The relative contribution of oil to maintaining structure is not quantified here.