Yes it sounds like slugs and I am sure the birds will will enjoy them, it was a good idea to tidy your strawberries!
Soil always has some slug eggs as they are an important part of the recycling system. Us gardeners always feel there are too many (!) but keeping the surface tidy is best practise to keep their numbers in balance. Digging is said to reduce slug eggs as birds can then eat them, but what is seldom mentioned is all the worms which are also eaten, and the loss of soil structure.