One of our three one-year-old muscovy hens seems ill. She's occasionally lethargic, lying down and resting on her own rather than walking around with her flock. The skin on her face is noticeably paler than her peers. Also, she often squints with one eye. She seems to eat, drink and lay eggs normally (we have three duck hens, and some days we get three new eggs in the nest). She's been like this for roughly a week. As of this moment, she seems worse than ever, because I was able to get closer to her than ever and snap the photo below: Any help will be much appreciated.