I have a question regarding a mallard pair. for the past 3 years, in spring, they have come to my yard for food, and swim in my koi pond. in March they showed up, and swam in my pond, but for some reason they will not go near my pond anymore. They still come here for food, and will sit in my yard all day, but will only drink and get into a small fountain bird bath, or drink from a bowl of water I set out for them. Can anyone tell me why they are avoiding my pond all of the sudden. I am very baffled.