Sitting ducks?

I was surprised to see a new lot of ducklings in the pond today. Ten days ago a family of five appeared, now down to four. There were four ducklings in the new batch. The mother duck looked a bit clueless though as she was standing on the edge hardly bothering with them. They were very small and vulnerable looking. 

Sad to say, when I went back to the pond this evening, the four had reduced in number - only three remain. Who is the duckling-snatcher? I haven’t seen the heron around for a while, so my money’s on the gulls.

How many will there be tomorrow?