We received 8 pilgrim geese at the end of May. We lost two a week ago and never figured out a cause. Today we lost three. There were no symptoms for any of them. They were happy, eating and drinking this morning when I put them in their pen. They were happily playing in their water when I left them. I came down an hour later to move the sprinkler in my garden and checked on them and three were dead. They are being fed game bird starter and their water dish is deep enough for them to put their whole head in. Any ideas?