Well something has had them, I suspect its squirrels but it might be mice or even Jays. I planted about 600 hazel nuts last month, each one was a viable nut as it was producing a little root. I planted them using the same technique as I used to plant the beech seeds. ie insert a bamboo cane into the ground, dig a small hole close to the cane, plant nut with root pointing down, carefully cover with soil, and finally place a plastic tube over the cane and press it down into the soil to provide some protection for the new plant. see link. Growing Beech from seeds.
This is what has happened, something has dug under the plastic tube, extracted the nut, split it in half and eaten the contents. In so doing it will have severed the root from the shoot and killed the new hazel plant.
Luckily I had a lot of hazel nuts left over and I planted these in the garden. I have now dug them up and planted them in pots and so I have about 300 replacements which I will probably plant out in the Autumn.
Also I found one hazel which had started to grow last year and then got eaten and has now reappeared. I quickly shoved a plastic tube over it so the same thing will not happen this year. So its 600 eaten and 1 has recovered!