We don’t know a lot about your specific situation or what you are seeing. All we can do is take blind shots that might help.
Have you examined each bird? Do you see any blood on any of them? If so, where? Blood should stain feathers. From what you posted you ASSUMED they didn’t have any wounds because they were on their perches.
Where was that pool of blood? Was it pure blood or did it have something else in it? On rare occasions a hen will pass some sloughed off intestines or such as that. I would not expect it to be pure blood but it can be bloody. It’s not a sign that she is about to die. She may be pretty healthy but for some reason just had a discharge.
You mentioned they may have sores on the combs, then the blood may have come from that. Is it an open wound that has scabbed over? It’s very possible one of them was pecked enough to draw blood or somehow scratched or cut itself on a sharp object. It’s even possible a predator raked the bird with a claw through a fence or an opening and the bird got away with just a minor wound. The red color of the combs and wattles comes from blood being very near the surface and the skin being very thin. They can bleed quite a bit from a minor comb or wattles wound. I’m guessing it is only one leghorn that has that appearance.
Do you know the symptoms of Coccidiosis? One possible symptom is blood in the stool. Coccidiosis does not always give bloody stools. You should see them puffed up and lethargic first but if you see bloody stools, it’s always a concern.
What have you been feeding them? Anything red? When I can beets I feed the chickens the cooked skins. First time I did that I thought they were pooping pure blood. Nope, just the beets.
A chicken will eat a mouse, frog, small snake, things like that. A lot of times they swallow them whole after pecking them to soften them up. If they are too big to swallow whole, they will peck them into pieces small enough to swallow. They don’t normally leave that carcass in one place long enough to form a pool of blood, more likely just a spot here and there. I doubt this is it but I’ll mention it.
As long as you cannot find any serious wounds and don’t see them acting strange, such as lethargic or losing weight, and it does not happen again, I would not worry about it all that much. If it is a wound that the others are pecking at (they can sometimes peck at a wound) I’d isolate the injured bird until it heals enough they stop pecking at it. It is a sign to maybe be on guard and observe their behaviors for a while.
A lot of shots in the dark. I don’t know if any of these fit your situation or if it is something else entirely.
