Not in(side) the hairs of their fur, on the hairs of their fur/in the entire fur. https://en.wikipedia.org/wiki/Vitamin_D#Evolution https://en.wikipedia.org/wik

Not in(side) the hairs of their fur, on the hairs of their fur/in the entire fur. https://en.wikipedia.org/wiki/Vitamin_D#Evolution https://en.wikipedia.org/wiki/Vitamin_D#Evolution: In birds and fur-bearing mammals, fur or feathers block UV rays from reaching the skin. Instead, vitamin D is created from oily secretions of the skin deposited onto the feathers or fur, and is obtained orally during grooming. So they take vitamin D orally, producing it on their bodies.