One of my Mallard ducks is a year old now and in the last day or so, she has been lying around a lot. She is eating and drinking fine and laying. But instead of wandering around with the others as she usually does, she is plopping herself down and not moving. She is usually kind of skittish and you can pretty well walk right up to her and she'll just move away a bit and then plunk down again. She gets up for treats like the rest, and then plunks down again. It has been 80-85F here, but they have lot's of shade and 2 pools to swim in. The other ducks are acting totally normal. Any ideas? Is it time for the vet? Any help/advice would be greatly appreciated. Thanks!