Can chickens get mildew on their tail feathers??

[JenniMcChick]

I was out-of-town last week. My husband took care of the girls & did a great job.
We received a lot of rain during that time. They have pellets in their raised coop & it's dirt, grass & some mulch in their covered run.
Ground slopes so run-off occurs & does not bog down their run.
They have stumps & a jungle gym in the run where they can get up off the wet ground also, if needed.
They do have 2 dust baths in there. The one in hollowed tree stump has sand mixed in since doesn't drain as well, but they don't like that one much & only sit in or perch on the edges when resting.
One of the other BO also has a tiny bit. Didn't notice any on the Production Blues, but with the black lacing, can't imagine it would be nearly as noticeable.
Anybody know what this is, what caused it &/or how to fix it if need be?
My initial research came up with "smudging" of the feathers & that it's normal. Although I've never had that happen on any of my previous BO chickens (been about 20).
But it was windy the day I took these pics. The when wind blew her tail feathers open & I saw the inside (underside of feathers) & can't imagine that's normal at all!
They are all eating, drinking & behaving normally.
Thank you so much in advance for any insight &/or advice offered!

 

[HollowOfWisps]

That is just their feather coloring. Not all have it, but it’s not uncommon for buffs to have flecks of black/brown on different feathers most commonly on their tail feathers.

 

[JenniMcChick]

That is just their feather coloring. Not all have it, but it’s not uncommon for buffs to have flecks of black/brown on different feathers most commonly on their tail feathers.

Odd & THANK YOU! Makes me feel much better!
Is that indicative of the quality of bird, I wonder?? I ordered all my previous ones & bought these at TSC. Just curious. I have noticed feather quality doesn't seem the same as the ones I bought years ago. Or maybe not purebred?
Or maybe while raising 3 kids I had more occupying my time back then & now with an empty nest I have time to notice & then fret about more minutae?!
Again, thank you!!