Unknown droppings

Unknown droppings

Observation - Unknown droppings - UK and Ireland. Description: These droppings were deposited on top of grouse droppings - there were others fairly nearby on their own. They appeared to have no 'texture', being very smooth; on first sight they looked rather slug-like. I previously put this observation under mammals,

These droppings were deposited on top of grouse droppings - there were others fairly nearby on their own. They appeared to have no 'texture', being very smooth; on first sight they looked rather slug-like.
I previously put this observation under mammals, but could it be a bird?