Just think of it as nature's way of telling you you have to many koi. On a serious note I used to have a little gold fish pond out in my backyard I looked out the window one day and saw a six foot high sand crane standing there. I thought it was a statue at first and then he took off. Another time a dark shadow fell over the ground and I glanced out and saw him coming in for a landing. I was amazed that a bird that big could spot a 1 inch gold fish in a pond that was about 6 feet by 6 feet.