Disappearing frogs (again).

[yorky]

We have a small garden pond that up until last year always had frogs. Then last year, for no apparent reason, the frogs disappeared -no bodies - nothing.
This was the situation until about six weeks ago, when suddenly frogs appeared again - maximum five in number and of various sizes up to and including large adult male.
Now they have all disappeared again without trace. Again, no bodies either on the surface or on the bottom of the pond.
What is going on here?
I should point out that we have had a garden pond for many years and once there were fish in it, but we gave those away. There is a small waterfall which operates through a filtration system (as there as always been) so I don't think there's any problem there.
The pond has never frozen over entirely because there is a floating heater that keeps a hole in any ice that forms.
Unfortunately, and to our dismay (and the garden birds horror) we are surrounded by about fifteen cats that in our opinion should be shot. No access to the pond from above -so discounting herons as the culprits.
Has anyone any idea about what is happening?

[Hedge Witch]

If it is cats, they wouldn't have eaten every last frog with no trace, I wouldn't have thought.

I assume the 15 cats won't have suddenly appeared out of the blue this year. And you had 5 frogs survive to adulthood that manage to appear. So I'm guessing if the frogs had mated, that would have been a successful outcome for the frog population, in spite of the cats.

There was a similar case in a local village pond recently. But I know these have mated and left, probably to return next year. I wonder if this is the case with you.