Could very well be,which we call Woelrats
Herons can swallow amazingly big prey and they're not too picky either,if it fits down their gullet...it had better watch out!
As for example this unfortunate goosling discovered...
On occasion they are too
greedy though and can actually suffocate on pikes or eals etc. which go down well enough,but don't come up again as easily(think barbed fins).
As to their cleverness,they have some good tricks indeed.
One being they always pick the last duckling...so that the others aren't too freaked out about it and will calmly swim by it again till it moves on or there are none left.
Mother nature can be a harsh teacher,but she is always so beautiful though,so we forgive her a lot.