Should I be concerned? Black poop from one of my birds

[Rooka_2]

I'm not sure what to think of this, the last two days I've found tar like black poop in my chicken/duck room.

Here's the thing, I moved them from their outdoor pen to their new indoor pen last Wednesday. They've never been in this room, It's the old milking room in our 100 year old barn. I live in Canada and have more than a few Silkies, which are not cold hearty in our climate. This room is attached to my heated rooms so I thought it would be perfect for the winter.
There was a bit of rusty metal, but I cleaned it all up really well before I put them in and put a ton of straw down.
This black poop could have been something from before Wednesday, they have a massive outdoor pen and I very easily could have missed it.
I Google searched black bird poop and it says something about metal poisoning, now I'm freaking out.
The walls in their new room are plastic on the bottom half. But the barn outside does need a fresh coat of paint and I know for certain, the paint under the red we originally put was a led based paint.
None of my chickens or ducks appear to be sick at all.
I asked on my local facebook chicken group and a lady said that feeding them berries or black sunflower seeds can turn their poop black, but they have had neither of those things this week.

Please tell me I don't have dying bird.

 

[Jaeden Mckinley]

Do you think your chickens are stressed?

Do they eat any dark black/purple foods?

It might just be diarrhea

 

[Rooka_2]

Do you think your chickens are stressed?

Do they eat any dark black/purple foods?

It might just be diarrhea

If anything, I feel like they should be less stressed. When it started snowing on Monday they wouldn't come out of their outdoor coop at all. They were hardly eating anything as I keep food and water outside to keep the mice out of the coop. By Wednesday I felt like they were stressed out enough that I wanted to move them to the indoor area. They're back at eating and drinking as normal. However, I do realize this space is beyond small compared to the two acre pen they're used to roaming around.
I do have a 100 foot indoor run that they will get access to here in the next couple weeks, but I currently have a goat and a bunch of geese I rescued hanging out in there under observation to make sure they don't have any issues before I put them in with my animals.