We have a flock of Buff Opingtons, 5 (4) hens about 13 months old and 1 rooster, probably around 6 months. They live in an 8x4x4 coop with a 15x7 covered run and they are let out of the run nearly every other day to forage. The last week and a half or so one of our hens started looking very SLIGHTLY (I reiterate SLIGHTLY) sick, her comb and wattles were pale and her eyes were squinted but not runny. Other than that she seemed in fine shape, not droopy, just a little slower than the rest. Last night I went into the coop and she was dead. Any idea what it could've been?