Diseased Bird: Dove with a unknown diseise

This Eurasian Collared Dove sat in my tree all day and didn’t move. Upon closer observation, it was extremely dark and wet looking. My initial thought was an oil-soaked bird, but that wouldn’t make sense in the middle of town. Its eyes were also kind of puffy. Any help on identifying the problem is greatly appreciated so I can tell my neighbor if he needs to take his large amounts of feeders down.