If the poops are consistent in their large shape and both are well formed, chocked full of hay bits (i.e., crumble upon squishing), and abundant, I wouldn’t be too concerned. Darker poops in the context of same diet could be due to how much one particular rabbit drinks or some about their GI composition, though this is coming from a non-vet. I speak from personal experience, as my Fable has dark poos all the time and she eats more hay than any other rabbit I know, leading her to hydrate a lot. I’ve tried pellet switching and such but the poop appearance remains consistent — darker relative to my Wick.

Are there any concerns with health-related behaviors, such as poop quality/amount, peeing, energy, etc.?