It's really frustrating, isn't it? I used to hate wildlife when it happened, and swore revenge every time. But I feel differently now.
Similar things happened to me too often, to get upset anymore. It's not the animals' fault, squirrels will always be squirrels, and birds will behave like birds.
When I leave things unprotected, I know that I am taking a chance, and it's my job to make sure that "accidents" don't happen.
But it's not too late to plant another batch, right now. You only lose a couple of months, and that's not much, when you look at a 15 year time-frame.
Whenever you plant fress moss, plant seeds, or create a miniature landscape, always protect it with a shield of wire mesh. You just build a tall cylinder around the pot, and put a lid on top, from the same material. You can get a large roll from Home Depot (galvanized iron screen, for about $40 - it will last you a lifetime), and it takes 5 minutes to build the protection.
I have a little fence around almost all of my small trees in bonsai pots. Mostly the shallow pots, or slabs, where the risk of kocking off the soil is greater. I started doing it two years ago, and the birds and squirrels never touched them again. The next challenge is to figure out a way to stop the rats from occasionally defoliating an entire tree. They do it once or twice a year, usually during summer, and have preference to certain species, such as maples. First, I started exterminating the rats, but I gave that up, since I figured that there may be a few million rats next door, in the Angeles National Forest, and killing 3 a week won't make a dent. Now I lean towards building the protective screen around every single tree that they seem to have a taste for. The good thing is that they don't care about conifers.