Blood in coop?
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That spot could have come from just about anything and given there was no stool with it to assume it was expelled that way and treat for a non-indicated issue would be impractical. Even with no visible injuries on the birds bleeding wounds can have occurred - especially as the birds were just moved and are likely doing a little jostling as they settle on who is who in the new surroundings (moves can cause a shift in pecking order to take place) or even just general rough housing, etc.
Until/unless you see more bleeding or other indications of a problem, I would let it be.