Sandhill cranes (Grus canadensis) have a natural plumage color of primarily grey with red on their head. Some individuals seek out iron-rich soil and use it to stain their feathers. It's speculated that this helps adults who are sitting on a nest blend in better as well as young adults who aren't so great at flying just yet. Sandhills and their European cousins, Grus grus, are the only two species of cranes documented doing this.
This particular individual I saw yesterday was stained so red it almost looked like it used blood or paint instead of soil!