underbelly/belly button area

[kk+chickens]

i’m not sure if this is in the right category...

i have 5 hens:
2 easter eggers that are about 9.5 y/o
2 caramel brahmas that are about 3.5 y/o
1 black australorp that is about 3.5 y/o

they all have this little scab thing where their belly buttons would be and i’m just wondering if that’s normal. the brahmas have some of the feathers around it kind of glued together. seems like since everyone has it, it’s probably normal but i’m also just curious what it’s about. chickens are cool so if anybody knows more, let me know. i appreciate it
i’m attaching a couple pics

 

[ChickenCanoe]

Occasionally chickens get roost sores. Usually they are from a rough roost surface.

 

[kk+chickens]

Occasionally chickens get roost sores. Usually they are from a rough roost surface.

any suggestions for how to help with that? should i not use wooden roosts? are there any other options?