There are many diseases that can affect our garden birds, but there's one in particular currently devastating greenfinch and chaffinch numbers. Trichomonas is a parasitic disease that causes lesions in the throat, making it difficult for a bird to swallow food. If you notice a lethargic bird with fluffed-up feathers that regurgitates its food and seems to have difficulty breathing or swallowing, it may well be suffering from Trichomonas.