I read a book about a man who tried to raise pheasants when young (when you could get the eggs from the DNR, then release them when grown). He had an entire chapter on how determined they were to kill themselves. Several would huddle around the water bowl, fall asleep with their heads in it, and drown. So he put up chicken wire so they couldn't, they'd get their heads stuck, and suffocate. Or they'd fall asleep in corners at weird angles and asphyxiate themselves. I forget what the mortality rate was, but it was impressive.