Natural oils might play a factor in terms of sheen, but iridescence is mostly specialized feather microstructures. Probably developed as a factor both in mating and predation, e.g., shifting light patterns can cause confusion.
Hummingbirds are a good example of ‘extreme directionality,’ meaning very bright iridescence only at certain angles in certain lighting. See, e.g., here.
Wonder what makes the feathers of starlings so shiny, compared to the Robin’s. Natural oils, or are they actually formed differently in structure??
Natural oils might play a factor in terms of sheen, but iridescence is mostly specialized feather microstructures. Probably developed as a factor both in mating and predation, e.g., shifting light patterns can cause confusion.
Hummingbirds are a good example of ‘extreme directionality,’ meaning very bright iridescence only at certain angles in certain lighting. See, e.g., here.