Dead frogs

I was at a local club water on Tuesday and there were about a dozen dead frogs around the banks.
Each one had a puncture mark in its back.
While we were there my Wife had a walk round and found another which wasn't there when we arrived. It still had colour to its eyes but it was dead. So it hadnt been dead for long.
It had one wound in its belly and its guts were protruding.
I cant work out what has caused this.
The water had been dragged but not within the last 10 days so that rules that theory out.
I believe that Herons eat frogs so another idea was done for.
I cant think of what would cause injuries like this. Surely any creature doing that would have eaten them aswell?
Anyone have any theories?

Dogs?

Our dog used to pick them up thinking I wanted them for my pond. He diodn't mean to harm them and wouldn't swallow them, they taste terrible apparently (unless you're French). They would just lie motionless, like they were dead, but half an hour after they'd hop off.

I think its herons i see it a lot on my local most killed for no aparent reason but usually its toads. I had a closer look and found the spawn gone so they kill the males any way. i surpose they cant tell the difference.

It could also be some horrible pratt with a pellet gun.

Steve, are you suggesting that Herons would only kill the frogs for the spawn? The frogs in my pond usually spawn in mid February so the timing is a bit out there.

There are not too many examples of wasteful killing in wildlife although it does of course happen with some species.

I can see the intervention of humans(using the term in it's loosest sense) here.

Your frogs could have the victim of either a rat or a kingfisher, but more than likely a young heron though. Adult herons have trouble with frogs, let alone a younster.

A hungry crow will also have a go at a frog, I've watched a crow try and try to grab a frog from my koi pond...eventually the bird succeeded by stabbing the frog through the body, dragging it out of the water whilst still impaled on it's beak and then eat it. Clever buggers.!!

Were the wounds just a single puncture ? No signs of teeth marks ?

Don't waste them...use them as a terrific eel bait. Either popped up with a slice of foam inside their mouths or hooked through the ass end and dropped in the marginal weed growth. I've had some big eels on dead frogs, several over 4lbs.....and one misty morning a couple of years ago I had a 19lb 7oz common on popped up dead frog. I thought I'd hooked the eel of a lifetime, until this huge great tail emerged.

Could be Magpies,
We recently had a duck nest on the pond and had 10 chicks hatch last Saturday.Sunday morning 4 were killed within a few minutes of each other.All 4 had their eyes pecked out and their stomachs punctured,but were not carried off.Later on I found it was the Magpie nesting nearby.
There's only 4 chicks left now,time to get the gun out!

Herrons,seen it loads.

Thanks lads, I thought herons would have eaten them but I bow to your superior knowledge. )
There is a heron which is almost resident there so it does make sense.
Very interesting about eel bait Richard. Cant see me rushing out to find some more dead frogs though!

I don't think it could be dogs or cats. They pick frogs up and carry them without hurting them.