Dead ducklings!!

[wildturkey035]

I had 2 female mallard ducklings (about 1.5 months old) and today I observed them playing in their pool and having fun!.... I returned an hour later to find one dead and the other clinging to life (she so died later) one was a little torn up (feathers missing) but NO blood at all. The cage wasn't damaged and it DOES HAVE A METAL TOP ...so I assume a predator bird couldn't have done it.? Any ideas on what did it? Snakes? Bees? Wasps? We are in southwest wi..
Any ideas would be appreciated

 

[Island Roo]

How big are the holes in the enclosure?
Mink, weasel, rats?
A racoon can reach his dirty paws thru a small hole.