Sandhill Cranes Painting Their Feathers

Sandhill Cranes commonly paint their feathers. But why? The common belief is that they do it to camouflage their feathers but one wonders if they do it for some other reason. The mud found here in SE Minnesota is black and not red but maybe it's tannins from roots that make their feathers rust colored? This pair seemed to be rubbing mud/roots into their feathers.
The footage was all filmed in 4k 120p, then slowed to 20 percent.

[@moniqueaftertrucking]

Hello watching a colt and family in Florida- why do they paint?